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Stridulation and its significance in the waterbug genus Cenocorixa Jansson, Antti Risto Ilmari 1971

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STRIDULATION AND ITS SIGNIFICANCE IN THE WATERBUG GENUS CENOCORIXA by ANTTI RISTO ILMARI JANSSON B . S c , U n i v e r s i t y of H e l s i n k i , 1 9 6 4 M.Sc., U n i v e r s i t y of H e l s i n k i , 1 9 6 5 L i e . P h i l . , U n i v e r s i t y of H e l s i n k i , 1 9 6 8 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Zoology We accept t h i s t h e s i s as conforming to the req u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA January, 1 9 7 1 In present ing t h i s thes is in p a r t i a l f u l f i l m e n t o f the requirements for an advanced degree at the Un ive rs i t y of B r i t i s h Columbia, I agree that the L i b r a r y sha l l make i t f r e e l y a v a i l a b l e for reference and study. I fu r ther agree that permission for extensive copying o f t h i s thes is fo r s c h o l a r l y purposes may be granted by the Head of my Department or by h is representa t ives . It i s understood that copying or p u b l i c a t i o n o f th is thes is f o r f i n a n c i a l gain sha l l not be allowed without my wr i t ten permiss ion . Department of Zoology The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date 2 F e b . 1971 i STRIDULATION AND ITS SIGNIFICANCE IN THE WATERBUG GENUS CENOCORIXA Ab s t r a c t S t r i d u l a t i o n i n the waterbug genus Cenocorixa was studied i n the f i e l d and experimentally i n the l a b o r a t o r y . I t was shown tha t both males and females s t r i d u l a t e . The s t r i d u l a t o r y s i g n a l s , analysed by use of a sound spectro-graph, were shown to be species and sex s p e c i f i c , d i f f e r i n g i n temporal p a t t e r n of pulses, pulse r a t e , pulse s t r u c t u r e , and s i g n a l l e n g t h . I t was shown that the annual rhythm of s t r i d u l a t i o n i n both male and female i s c o r r e l a t e d w i t h sexual maturity. Males w i l l spontaneously s t r i d u l a t e when there i s mature sperm i n the t e s t e s , and t h i s occurs i n s p r i n g , e a r l y summer, and l a t e f a l l . Females do not s t r i d u l a t e spontaneously, but can be induced to s t r i d u l a t e when they have chorionated eggs i n the l a t e r a l oviducts, but no sperm i n the receptaculum seminis; they are s e x u a l l y mature only i n the sp r i n g and e a r l y summer. S t r i d u l a t i o n was shown to be important i n behavior l e a d i n g to s u c c e s s f u l c o p u l a t i o n . Male s t r i d u l a t i o n f u n c t i o n s as a c a l l i n g s i g n a l f a c i l i t a t i n g p a i r - f o r m a t i o n by a t t r a c t i n g c o n s p e c i f i c females, and as an a g o n i s t i c s i g n a l s e r v i n g to space out i n d i v i d u a l s . Males w i l l answer almost any s t r i d -u l a t o r y s i g n a l , but only c a l l s from a c o n s p e c i f i c female i n i t i a t e searching behavior. Receptive females respond to s t r i d u l a t o r y s t i m u l i from c o n s p e c i f i c males by s t r i d u l a t i n g , and s u c c e s s f u l c o p u l a t i o n s were observed only when preceded i i by such s i g n a l r e c o g n i t i o n ; female s t r i d u l a t i o n f u n c t i o n s as an agreement s i g n a l . S t r i d u l a t i o n serves as a premating i s o l a t i n g mechanism i n Cenocorixa. However, i t i s not the only i s o l a t i n g mechanism, but i s r e i n f o r c e d by geographic and e c o l o g i c a l i s o l a t i o n i n a number of cases. The C o r i x i d a e , since they mostly have only a s i n g l e s t r i d u l a t o r y s i g n a l that can f u n c t i o n i n at l e a s t two contexts, are considered to represent a p r i m i t i v e stage i n e v o l u t i o n of s t r i d u l a t o r y s i g n a l s : a stage i n which f u n c t i o n a l d i v e r s i f i c a t i o n of s i g n a l s i s j u s t e v o l v i n g . i i i TABLE OF CONTENTS Page ABSTRACT i TABLE OF CONTENTS i i i LIST OF TABLES v LIST OF FIGURES v i ACKNOWLEDGEMENTS x i I. INTRODUCTION 1 I I . MATERIAL AND METHODS 1. Sampling and handling of specimens 9 2. L i f e c y c l e 10 3. S t r i d u l a t i o n 1 3 4. Behavior 1 9 I I I . RESULTS 1. Mechanism of sound production and morphology of the s t r i d u l a t o r y apparatus 2 3 2. Audiospectrographic a n a l y s i s of the s t r i d -u l a t o r y s i g n a l s 29 a) General 29 b) D e s c r i p t i o n of the s i g n a l s 3 2 c) E f f e c t of temperature on s t r i d u l a t i o n . 4 3 d) Sounds produced as byproduct of c l e a n -i n g movements 6l 3. L i f e c y c l e , annual rhythm of s t r i d u l a t i o n , and gonad development 6 3 a) L i f e c y c l e . 63 b) Gonad development 7 6 c) Annual rhythm of s t r i d u l a t i o n 8 9 d) Miscellaneous observations on other species and l o c a l i t i e s 9 3 4. D i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y 96 5. B e h a v i o r a l r o l e of s t r i d u l a t i o n 104 i v a) Male and female response to s t r i d -u l a t o r y s i g n a l s and some other sti m -u l i 104 b) Mating i n C. b i f i d a 114 c) S p e c i f i c d i f f e r e n c e s i n the mating behavior 1 1 8 d) Species r e c o g n i t i o n 1 2 6 6. Geographic d i s t r i b u t i o n and notes on ecology and h a b i t a t s of the species 1 3 5 a) Data on d i s t r i b u t i o n and notes on ecology 1 3 5 b) Notes on e c o l o g i c a l i s o l a t i o n i n sympatric s i t u a t i o n s 144 IV. DISCUSSION 1. Mechanism of sound production and a n a l y s i s of the s i g n a l s 147 2 . L i f e c y c l e , sexual maturation, and s t r i d -u l a t i o n 1 5 9 3 . S t r i d u l a t o r y behavior 1 7 1 4 . E v o l u t i o n a r y s i g n i f i c a n c e of s t r i d u l a t i o n i n the genus Cenocorixa. l 8 l 5 . E v o l u t i o n and s t r i d u l a t i o n i n C o r i x i d a e . . . 1 8 8 V. SUMMARY 1 9 8 VI. LITERATURE CITED 2 0 0 APPENDIX I . SYSTEMATIC NOTES AND NEW SYNONYMY IN THE GENUS CENOCORIXA 2 0 7 APPENDIX I I . AUDIOSPECTROGRAPHIC ANALYSIS OF THE STRIDULATORY SIGNALS OF SOME NORTH AMERICAN CORIXIDAE FOUND SYMPATRIC WITH CENOCORIXA 2 3 1 V LIST OF TABLES Table Page I. Thickness of the pegs of the pars s t r i d e n s and comparison of the number of peg rows on the pars s t r i d e n s and the number of impacts per pulse 27 I I . Numerical c h a r a c t e r i s t i c s of Cenocorixa s i g n a l s . . . 3 1 I I I . A c t i v i t i e s of _C. b i f i d a males under various t e s t c o n d i t i o n s 1 1 0 IV. A c t i v i t i e s of C_. b i f i d a females under various t e s t c o n d i t i o n s 1 1 2 V. Distance f o r r e c o g n i t i o n of s i g n a l s of opposite sex i n some Cenocorixa species i n sand l i n e d bathtub 1 1 9 VI. S p e c i f i c d i f f e r e n c e s observed i n mating be-havi o r of Cenocorixa males 1 2 0 V I I . S p e c i f i c d i f f e r e n c e s observed i n mating be-havi o r of Cenocorixa females 1 2 1 V I I I . Response of Cenocorixa males to playback of male s i g n a l s 1 3 0 IX. Response of Cenocorixa males to playback of female s i g n a l s 1 3 1 X. Response of Cenocorixa females to playback of male s i g n a l s 1 3 2 XI. Response of Cenocorixa females to playback of female s i g n a l s 1 3 3 X I I . Response of Cenocorixa spp. to playback of s i g n a l s of sympatric species of other Co r i x i d a e ' 1 3 4 X I I I . Estimates of the magnitude of d i f f e r e n t i s o -l a t i n g mechanisms i n Cenocorixa 1 8 7 v i LIST OF FIGURES Figure Page 1. Terminology used i n the d e s c r i p t i o n s of the s t r i d u l a t o r y s i g n a l s 1 5 2. Stereoscan photograph of the f r o n t l e g of (J. b l a i s d e l l i male showing the l o c a t i o n of the pars s t r i d e n s 24 3. Stereoscan photograph of the head of CJ. b l a i s d e l l i female showing the l o c a t i o n of the plectrum 2 5 4. Stereoscan photographs of the s t r i d u l a t o r y apparatus of _C. b l a i s d e l l i 2 8 5. Sound spectrograms of C_. b i f i d a s i g n a l s , 3 8 6. Sound spectrograms of C_. k u i t e r t i s i g n a l s 3 8 7. Sound spectrograms of CJ. andersoni s i g n a l s 3 9 8. Sound spectrograms of CJ. utahensis s i g n a l s 3 9 9. Sound spectrograms of _C. dakotensis s i g n a l s 40 10. Sound spectrograms of C_. b l a i s d e l l i s i g n a l s 40 1 1 . Sound spectrogram of C_. b l a i s d e l l i mounting s i g n a l 4 l 1 2 . Sound spectrograms of CJ. wileyae s i g n a l s 42 1 3 . Sound spectrograms of CJ. e x p l e t a s i g n a l s 42 14. E f f e c t of temperature on s i g n a l d u r a t i o n i n C_. b i f i d a , C. k u i t e r t i , and CJ. andersoni 45 1 5 . E f f e c t of temperature on s i g n a l d u r a t i o n i n C_. utahensis, C_. dakotensis, and C_. b l a i s d e l l i . ... 46 1 6 . E f f e c t of temperature on s i g n a l d u r a t i o n i n (J. wileyae and CJ. expl e t a 47 1 7 . E f f e c t of temperature on pulse r a t e i n CJ. b i f i d a s i g n a l s 48 1 8 . E f f e c t of temperature on pulse ra t e i n CJ. k u i -t e r t i male s i g n a l s . . . . 49 1 9 . E f f e c t of temperature on pulse ra t e i n (J_. andersoni male s i g n a l s 5 0 v i i F igure Page 2 0 . E f f e c t of temperature on pulse r a t e i n C_. andersoni and C_. utahensis female s i g n a l s 51 2 1 . E f f e c t of temperature on pulse r a t e i n C_. utahensis male s i g n a l s 52 2 2 . E f f e c t of temperature on pulse r a t e i n C_. dakotensis s i g n a l s 53 2 3 . E f f e c t of temperature on pulse r a t e i n C_. b l a i s d e l l i s i g n a l s 5 4 2k. E f f e c t of temperature on pulse r a t e i n _C. wileyae male s i g n a l s 55 2 5 . E f f e c t of temperature on pulse r a t e i n C_. wileyae female s i g n a l s 56 2 6 . E f f e c t of temperature on pulse r a t e i n C_. exp l e t a s i g n a l s 57 2 7 . E f f e c t of temperature on r e p e t i t i o n r a t e of "unipulsate pulse groups" of the second p a r t of the s i g n a l i n _C. b l a i s d e l l i male 58 2 8 . E f f e c t of temperature on r e p e t i t i o n r a t e of pulse groups of the second par t of the s i g n a l i n C_. wileyae male 59 2 9 . E f f e c t of temperature on r e p e t i t i o n r a t e of pulse groups of the s i g n a l s i n _C. e x p l e t a 60 3 0 . Sound spectrograms of sounds produced as a byproduct of c l e a n i n g movements 62 3 1 . Sequence of generations of C.. b i f i d a i n East Lake according to standard sweep samples i n 1 9 6 9 . . 6 6 3 2 . Sequence of generations of £. b i f i d a i n Long Lake according to standard sweep samples i n I 9 6 9 . . 6 7 3 3 . Sequence of generations of C_. e x p l e t a i n LB2 according to standard sweep samples i n 1969 68 3 4 . D a i l y maximum and minimum temperatures at West-wick Lake and Boitano Lake during the summer of ' 1969 69 3 5 . D a i l y maximum and minimum temperatures i n f i v e lakes i n the i n t e r i o r B r i t i s h Columbia during the summer of 1969 70 v i i i F i gure Page 3 6 . S p e c i f i c c o n d u c t i v i t y of surface water i n eight water bodies i n the i n t e r i o r B r i t i s h Columbia during the summer of 1969 71 3 7 . Sequence of generations of £. andersoni i n Custer g o l f course pond according to standard sweep samples i n 1970 74 3 8 . D a i l y maximum and minimum temperatures at Surrey M u n i c i p a l H a l l Weather S t a t i o n , B r i -t i s h Columbia, during the pe r i o d of November 1969 - October 197O 75 39- L i g h t microscope photographs of stages of ova r i a n development i n C_. b i f i d a 77 40. L i g h t microscope photographs of stages of spermatogenesis i n C_. b i f i d a 78 41. Presence of s e x u a l l y mature specimens of C_. b i f i d a i n East Lake and Long Lake i n 1969 8 l 42. Presence of s e x u a l l y mature specimens of C_. e x p l e t a i n LB2 i n 1969 82 4 3 . Presence of s e x u a l l y mature specimens of _C. andersoni i n Custer g o l f course pond during the summer of 1970 84 4 4 . L i g h t microscope photograph of a f o l l i c l e from an a r r e s t e d t e s t i s of _C. b i f i d a 87 4 5 . L i g h t microscope photograph of a f o l l i c l e from a mature t e s t i s of _C. b i f i d a 88 46. Observed annual rhythm of s t r i d u l a t i o n and sex-u a l m a t u r i t y i n four species of Cenocorixa 92 47. In s i t u observations on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of C_. b i f i d a and _C. exple ;; : eta 99 48. Laboratory experiments on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of _C. b i f i d a , _C. k u i t e r t i , and C_. wileyae 1 0 0 49. Laboratory experiment on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of _C. andersoni 1 0 1 5 0 . Laboratory experiments on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of C.. dakotensis and C. e x p l e t a 1 0 2 i x re Page 5 1 . Laboratory experiment on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of (J_. b l a i s d e l l i 1 0 3 5 2 . R e p e t i t i o n r a t e of s i g n a l s produced by 1 0 male specimens i n a sample four minute t e s t p e r i o d . . . . 1 0 5 5 3 . Diagram on the sequence of events i n a s u c c e s s f u l mating i n _C. b i f i d a 1 1 7 5 4 . Known geographic d i s t r i b u t i o n of (J. b i f i d a and C. k u i t e r t i 140 5 5 . Known geographic d i s t r i b u t i o n of CJ. andersoni and (J_. utahensis l 4 l 5 6 . Known geographic d i s t r i b u t i o n of (J_. dakotensis and C_. b l a i s d e l l i 142 5 7 . Known geographic d i s t r i b u t i o n of C_. wileyae and (J. e x p l e t a 1 4 3 5 8 . Example of a r t i f a c t s created by improper a n a l -y s i s of a Cenocorixa s i g n a l 1 5 1 5 9 - Summary of the r e g r e s s i o n l i n e s of temperature e f f e c t on pulse r a t e i n Cenocorixa male s i g n a l s . . 1 5 4 6 0 . Summary of temperature e f f e c t on s i g n a l d u r a t i o n i n Cenocorixa males 1 5 6 6 1 . Summary of the d i e l p e r i o d i c i t y of the s t r i d -u l a t i n g a c t i v i t y of Cenocorixa males 1 8 4 6 2 . Diagram of suggested i n c r e a s i n g complexity of s i g n a l s of Cenocorixa males 1 8 9 6 3 . Suggested evolution' of Cenocorixa species 1 9 1 APPENDIX I : 64 . Dorsal view of p o s t e r i o r abdominal terg a of male i n CJ. b i f i d a and (J_. k u i t e r t i 2 1 9 65.. Dorsal view of p o s t e r i o r abdominal terg a of male i n (J_. andersoni and (J. utahensis 2 2 0 6 6 . Dorsal view of p o s t e r i o r abdominal terga of male i n CJ. dakotensis and CJ. b l a i s d e l l i 2 2 1 6 7 . Dorsal view of p o s t e r i o r abdominal terga of male i n C. wileyae and C_. e x p l e t a 2 2 2 X Figure Page 6 8 . I n t r a s p e c i f i c v a r i a t i o n i n arrangement of p a l a r pegs i n C_. b i f i d a 2 2 3 6 9 . Arrangement of p a l a r pegs In C_. k u i t e r t i , C_. andersoni, C_. utahensis, and S_. dakotensis 224 7 0 . Arrangement of p a l a r pegs i n C_. b l a i s d e l l i , C_. wileyae, and C_. e x p l e t a 2 2 5 7 1 . T y p i c a l shapes of the r i g h t parameres i n Cenocorixa species 2 2 6 7 2 . I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere i n C_. b i f i d a 2 2 7 7 3 - I n t r a s p e c i f i c v a r i a t i o n i n shape of f i g h t paramere of _C. k u i t e r t i and C_. andersoni 2 2 8 7 4 . I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere i n C_. utahensis, C_. dakotensis, and C_. b l a i s d e l l i 2 2 9 7 5 - I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere i n _C. wileyae and C_. e x p l e t a 2 3 0 APPENDIX I I : 7 6 . Sound spectrograms of the male c a l l s of C o r i -s e l l a t a r s a l i s and C a l l i c o r i x a v u l n e r a t a 2 3 5 77- Sound spectrograms of the male c a l l s of C a l l i c o r i x a audeni and C_. t e t o n i 2 3 5 7 8 . Sound spectrograms of the s i g n a l s of Sigara omani and S. nevadensis 2 3 6 x i ACKNOWLEDGEMENTS The author wishes to express h i s most s i n c e r e g r a t i t u d e to Dr. G. G. E. Scudder f o r h i s encouragement, guidance, and c r i t i c a l s u p e r v i s i o n during the e n t i r e phase of t h i s work. Thanks are a l s o due to Dr. N. R. L i l e y f o r c r i t i c a l d i s -cussions on behavioral problems. A l s o Drs. A. B. Acton and J. D. McPhail read the manuscript. Mr. L. Veto's a s s i s t a n c e i n using the Scanning e l e c t r o n microscope, and Mrs. D. Lauriente's programming and computing of the pulse r a t e data, are appreciated. S p e c i a l thanks are due to my wife who allowed me to spend " a l l " my time i n preparing t h i s t h e s i s . F i n a n c i a l support f o r the study was obtained from the f o l l o w i n g : N a t i o n a l Research Council of Canada (through Dr. G. G. E. Scudder), The U n i v e r s i t y of B r i t i s h Columbia, The U n i v e r s i t y of H e l s i n k i , F i n l a n d , and Werner H a c k l i n Foundation, P o r i , F i n l a n d . i) 1 I. INTRODUCTION During the past hundred years a considerable l i t e r a t u r e has accumulated on i n s e c t sounds. The e a r l y studies on these sounds, however, were only notes on the d i f f e r e n t sounds produced by var i o u s species, and suggestions on the mode of production of these sounds. I t i s only during the l a s t 30 years that t e c h n i c a l apparatus has been developed and thorough i n v e s t i g a t i o n s on b i o a c o u s t i c s undertaken by p h y s i o l -o g i s t s and e t h o l o g i s t s . These studies have r e s u l t e d i n a) thorough d e s c r i p t i o n of the mechanism of sound production, b) d e t a i l e d a n a l y s i s of the s i g n a l s , and c) playback exper-iments using p r e v i o u s l y recorded or a r t i f i c i a l s i g n a l s . In i n s e c t s , according to Dumortier (1963 a) three d i f f -erent mechanisms of sound production can be d i s t i n g u i s h e d : 1) Sound production as a byproduct of some other normal a c t i v i t y , e.g. f l i g h t sound; 2) Sound production by per-cussion on the substratum, e.g. the knocking of the Death Watch Beetles (Anobiidae); 3) Sound production by a s p e c i a l sound producing apparatus. The apparatus f o r sound production i s oft e n a very s p e c i a l i z e d organ, and Dumortier (1963 a ) separates the f o l l o w i n g three c l a s s e s : a) Sound production by passage of f l u i d (gas or l i q u i d ) across an o r i f i c e , e.g. Death's Head Moth (Acherontia atropos L.) i s sa i d to blow a i r i n and out through i t s pharynx, producing w h i s t l i n g sounds; b) Sound production by v i b r a t i o n of a membrane (other than wings), e.g. r e p r e s e n t a t i v e s of Homoptera have a membrane 2 where a s p e c i a l muscle i s attached and c o n t r a c t i o n s of t h i s muscle cause the membrane to v i b r a t e ; c) Sound production by f r i c t i o n , e.g. c r i c k e t s (Orthoptera, Gryllodea) make sounds by rubbing c e r t a i n p a r ts of t h e i r wings against each other. Sound production by f r i c t i o n i s the most widespread mechanism used i n i n s e c t s . I t i s o f t e n c a l l e d s t r i d u l a t i o n and t h i s usage i s adopted h e r e i n ; e t y m o l o g i c a l l y , however, t h i s term can be a p p l i e d to any sound production. The s t r i d u l a t o r y apparatus i s composed of two p a r t s : a "pars s t r i d e n s " ( a . - f i l e , a s t r i g i l ) , a s p e c i a l s t r i d u l a t o r y surface w i t h pegs, t e e t h , or spines, and a "plectrum", a sharp edge, a tooth, or a l i n e of d e n t i c u l a t i o n s . The sound i s produced by the rubbing of the plectrum on the pars s t r i d e n s or v i c e versa. In f a c t , the d i s t i n c t i o n of the parts i s r a t h e r a r t i f i c i a l and o f t e n i t i s impossible to say which i s which. Several attempts have been made to c l a s s i f y the b i o l -o g i c a l f u n c t i o n of s t r i d u l a t o r y s i g n a l s i n i n s e c t s (e.g. Busnel, 1963; Dumortier, 1963 c; H a s k e l l , 1964; Alexander, 1967). A l l of these c l a s s i f i c a t i o n s are based p r i m a r i l y on studies on Orthoptera, and some Orthopteran species have s e v e r a l d i f f e r e n t c a l l s apparently having d i f f e r e n t f u n c t i o n s . However, i n most other i n s e c t s only one or two s i g n a l s are known, and the f u n c t i o n of these s i g n a l s may be d i f f i c u l t to c l a s s i f y according to the e x i s t i n g c l a s s i f i c a t i o n s . F u n c t i o n a l l y , s i g n a l s which are c l a s s i f i e d as c a l l i n g , r i v a l ' s , or premating songs, may a l s o have an important r o l e i n sexual i s o l a t i o n of c l o s e l y r e l a t e d species. This has been 3 shown i n s e v e r a l cases of v e r t e b r a t e s (e.g. D i l g e r , 1956; Marler, 1957; L i t t l e John and Michaud, 1959; Delco, i 9 6 0 ) . G e n e r a l l y these cases f a l l i n t o the category of premating i s o l a t i n g mechanisms since the males produce species s p e c i f i c s i g n a l s which a t t r a c t c o n s p e c i f i c females. Females of other species do not respond, and thus p a i r formation i s f a c i l -i t a t e d by the s i g n a l s . In i n s e c t s such studies have been c a r r i e d out mostly on Orthoptera (e.g. Walker, 1957; Per-deck, 1958; H a s k e l l , I 9 6 I ; Spooner, 1968) . In the water'bug f a m i l y Corixidae i t has been known f o r more than 120 years that some species are able to s t r i d u l a t e while completely submerged. The f i r s t note on t h i s phenomenon was published by B a l l ( 1 8 46), who made observations on the sounds .of Corixa s t r i a t a (L.) [= S i g a r a s t r i a t a (L.)] In England. A f t e r t h i s , other notes on s t r i d u l a t i o n of European Corixidae were published (e.g. Thomson, 1894; Carpenter, 1894; K i r k a l d y , 1901), d e s c r i b i n g the q u a l i t y of the sound (as i t i s heard by the human e a r ) , and i t s apparent mode of production. A l l these notes concerned the subfamily C o r i x i n a e * , and the mechanism was described i n c o r r e c t l y . M i t i s (1936) came c l o s e s t to the t r u t h by s t a t i n g that the sound was produced by rubbing c e r t a i n s t r i d u l a t o r y areas of the f r o n t femora against the sharp edges of the head about midway between the antennae and labium; the former part being c a l l e d plectrum and the l a t t e r pars s t r i d e n s . However, u s u a l l y the * The f a m i l y Corixidae i s taxonomically d i v i d e d i n t o s i x s u b f a m i l i e s : Diaprepocorinae, Micronectinae, Stenocorixinae, Cymatiinae, H e t e r o c o r i x i n a e , and C o r i x i n a e . For more d e t a i l s see Hungerford (1948). 4 plectrum i s a sharp edge, and the pars s t r i d e n s i s the p a r t c o n t a i n i n g the s t r i d u l a t o r y pegs, and thus M i t i s ' ( 1 9 3 6 ) terminology w i l l be reversed i n the present study. [For a more d e t a i l e d review of the e a r l y works d e s c r i b i n g the method of sound production i n C o r i x i d a e , see Finke ( 1 9 6 8 ) ] M i t i s ( 1 9 3 6 ) compared the sexes of c e r t a i n Corixinae and found that only the male had s t r i d u l a t o r y areas l o c a t e d on the i n s i d e of the f r o n t femur that contained s e v e r a l rows of short pegs; these pegs were s a i d to be absent from the female. Further, M i t i s ( 1 9 3 6 ) observed only males to s t r i d -u l a t e , and t h i s has been concluded a l s o i n other studies (e.g. S c h a l l e r , 1 9 5 1 ; Leston and P r i n g l e , 1 9 6 3 ) . In only two species have p o s s i b l e female c a l l s been reported: Leston ( i n H a s k e l l , 1 9 5 7 ) and Southwood and Leston ( 1 9 5 9 ) c l a i m that both sexes of A r c t o c o r i s a germari (Fie'b.) s t r i d u l a t e during the mating p e r i o d , but nothing more i s s a i d about the s t r i d u l a t i o n of t h i s species. Finke ( 1 9 6 8 ) observed some unusual f a i n t s i g n a l s i n c u l t u r e s of Sigara s t r i a t a ( L . ) , but was unable to o b t a i n s a t i s f a c t o r y recordings. However, she observed that both males and females produced these sounds and the mode of production was by rubbing the hind legs against the f o r e wings l y i n g above the abdomen. A l s o Moore ( 1 9 6 1 ) observed and recorded sounds' produced i n a s i m i l a r way by males of two species of North American C o r i x i d a e , Hesperocorixa atopodonta (Hung.) and Sigara g r o s s o l i n e a t a Hung.; no movements of the f r o n t l e g s were observed during these s t r i d u l a t i o n s . M i t i s ( 1 9 3 6 ) compared the morphology of the s t r i d -5 u l a t o r y areas on the f r o n t femora of males of se v e r a l species. He found that the thickness of the pegs c o r r e l a t e w i t h the loudness of the sounds produced (as judged by the human ea r ) : the t h i c k e r the pegs the louder the s i g n a l . Further, he found t h a t the subfamily Corixinae contains both s t r i d u l a t i n g and n o n s t r i d u l a t i n g species, and according to the s t r u c t u r e of the pegs on f r o n t femora he was able to p r e d i c t i f a species was able to s t r i d u l a t e . A s i m i l a r comparison of the s t r i d u l a t o r y areas was made by Hungerford ( 1 9 ^ 8 ) , who gave a l i s t of 7 5 western hemisphere species of Corixinae supposed to s t r i d u l a t e although observations of a c t u a l s t r i d u l a t i o n e x i s t f o r only one of them. In c o n t r a s t to the subfamily C o r i x i n a e , s e v e r a l species of the genus Micronecta (subfamily Micronectinae) have been observed to s t r i d u l a t e although they do not have s t r i d -u l a t o r y pegs on the f r o n t femora. M i t i s ( 1 9 3 6 ) and South-wood and Leston ( 1 9 5 9 ) suggest that they produce the sound by a s t r i g i l , an organ l o c a t e d d o r s a l l y on the s i x t h abdominal segment: t h i s organ would be rubbed against the tergum of the f i f t h segment or against some parts of g e n i t a l i a . Males of most species of the subfamily Corixinae a l s o have the s t r i g i l , but i t s f u n c t i o n seems to be f o r a t t a c h i n g to the female during c o p u l a t i o n (Larsen, 1 9 3 8 ) . C o r ixinae and Micronectinae are the only s u b f a m i l i e s of C o r i x i d a e i n which s t r i d u l a t i n g species have been reported so f a r . Representatives of Cymatiinae (genus Cymatia) are known to be unable to s t r i d u l a t e ( M i t i s , 1 9 3 6 ) , and observ-at i o n s on other s u b f a m i l i e s are l a c k i n g . 6 Only three p u b l i c a t i o n s e x i s t on audiospectrographic a n a l y s i s of s i g n a l s of Cori x i n a e . Moore (1961) gives sound spectrograms of s i g n a l s produced by Hesperocorixa atopodonta, and from h i s f i g u r e i t i s p o s s i b l e to see that the s t r i d -u l a t i o n of t h i s species i s composed of more or l e s s i r r e g u l a r p u l ses, the main frequency area of the sound being 7-8 k i l o c y c l e s per second. H a s k e l l (1961) gives o s c i l l o g r a m s of two c a l l s produced by Sig a r a d o r s a l i s (Leach.). These f i g u r e s do not give any i n f o r m a t i o n on the frequency of the sound, but i t can be seen that one of the s i g n a l s i s composed of r e g u l a r l y repeated pulses, while the other one i s composed of pulse groups repeated with r e g u l a r i n t e r v a l s . Finke (1968) gives both spectrograms and osc i l l o g r a m s of the c a l l s of two species, Sigara s t r i a t a (L.) and C a l l i -c o r i x a praeusta (Fie'b.). In these f i g u r e s the c a l l s of S_. s t r i a t a appear to be very much l i k e the c a l l s of S_. d o r s a l i s i n H a s k e l l (1961), while C_. praeusta only has one c a l l , t h i s being composed of two p a r t s , each w i t h r e g u l a r l y repeated p u l s e s , but w i t h d i f f e r e n t pulse r a t e . The main frequency area f o r both species i n Finke's (1968) study appear to be 3-6 kc/sec, w i t h some higher overtones up to 16 kc/sec and over. Hagemann (19IO) described the tympanal organ of Cori x i d a e l o c a t e d near the wing base on the mesothorax. S c h a l l e r (1951) demonstrated i n various experiments that a c o u s t i c s t i m u l i are rec e i v e d by t h i s organ, although i t a l s o might have a f u n c t i o n as a h y d r o s t a t i c pressure i n d i c a t o r . 7 The f u n c t i o n of s t r i d u l a t i o n i n Corixinae has been discussed a number of times. Because i t i s commonly observed that these i n s e c t s s t r i d u l a t e during the breeding season ( M i t i s , 1 9 3 6 ; S c h a l l e r , 1 9 5 1 ; Finke, 1 9 6 8 ; Jansson, 1968) and have species s p e c i f i c s i g n a l s , i t . i s supposed that the song i s combined with sexual behavior. S c h a l l e r ( 1 9 5 1 ) r e p o r t s t h a t the song of male S_. s t r i a t a i s a c o u r t s h i p song causing females to swim r a p i d l y i n small c i r c l e s , which i s an e f f e c t i v e mechanism because the males attempt to copulate with any moving object of s u i t a b l e s i z e . A l s o Finke ( 1 9 6 8 ) observed an increase i n the swimming a c t i v i t y of the females i n the presence of the male signals.. However, Larsen ( 1 9 3 8 ) and Jansson ( 1 9 6 8 ) d i d not observe any v i s i b l e e f f e c t of the song of the males upon females. In a d d i t i o n , Larsen ( 1 9 3 8 ) observed males of Corixa dentipes (Thorns.) to s t r i d u l a t e both i n e a r l y s p r i n g and i n l a t e f a l l , and noted t h a t the l a t e f a l l s t r i d u l a t i o n i s not i n connection w i t h breeding. To date, no comprehensive study has been under-taken on the f u n c t i o n of s t r i d u l a t i o n i n t h i s group of water bugs. The aim of the t h e s i s i s to o b t a i n a more d e t a i l e d understanding of s t r i d u l a t i o n i n the C o r i x i n a e . The genus Cenocorixa Hungerford was chosen f o r study because i t contains s e v e r a l c l o s e l y r e l a t e d species which are o f t e n d i f f i c u l t to i d e n t i f y according to morphological characters ( c f . Appendix I) and which could be p r e d i c t e d to s t r i d u l a t e because they have s t r i d u l a t o r y pegs on the f r o n t femora. A l l species i n the genus a l s o have t h e i r geographic d i s t r i b u t i o n i n western 8 North America (Hungerford, 1 9 ^ 8 ) , and both a l l o p a t r i c and sympatric s i t u a t i o n s can be studied. Two species i n par-t i c u l a r , C_. b i f i d a (Hung. ) and C_. e x p l e t a (Uhler) are abundant i n B r i t i s h Columbia, where they occur a l l o p a t r i c -a l l y and s y m p a t r i c a l l y (Scudder, 1 9 6 9 a; 1 9 6 9 b), and so they were studied most i n t e n s i v e l y . 9 I I . MATERIAL AND METHODS 1. Sampling and handling of specimens The general d i s t r i b u t i o n of the species was determined from published records (Hungerford, 1948; Lansbury, I960; Scudder, 1969 a ) , then s p e c i f i c l o c a l i t i e s to be studied were s e l e c t e d f o r a l l the species. Bugs were c o l l e c t e d using a sweep net., and were transported to the l a b o r a t o r y i n one g a l l o n thermos jugs about h a l f f i l l e d w i t h l a k e water. In cases when the t r a n s -p o r t a t i o n took s e v e r a l days (from C a l i f o r n i a and Utah) the thermos Jugs were c a r r i e d i n styrofoam i c e chests c o n t a i n i n g m e l t i n g i c e ; i n t h i s way the bugs were kept at about 8-10°C during t r a n s p o r t a t i o n . In the l a b o r a t o r y the bugs were t r a n s f e r r e d to 30x24x10 cm transparent covered p l a s t i c t r a y s (henceforth c a l l e d c u l t u r e t r a y s ) w i t h about 4-5 l i t r e s of n a t u r a l l a k e water, so that the depth of the water was about 5 cm. Pieces of p l a s t i c screen were placed on the bottom of the c u l t u r e t r a y s to provide support f o r the bugs while r e s t i n g . Culture t r a y s were then kept e i t h e r i n a constant temperature cabinet at 5°0 u n t i l needed, or i n the l a b o r a t o r y at a temperature of about 21-24°C (room temperature) f o r v a r i o u s experiments. Photoperiod i n both cases was 16 hours a r t i f i c i a l l i g h t per day, except i n experiments r e q u i r i n g n a t u r a l l i g h t c o n d i t i o n s . At 5°C the bugs survived s e v e r a l months without any a t t e n t i o n . At room temperature they were fed d a i l y on f r o z e n b r i n e shrimp [Artemia s a l i n a ( L . ) , L o n g l i f e F i s h Food Products, Div. of 1 0 Sterno I n d u s t r i e s Inc., H a r r i s o n , N.J.]. Three of the species studied, C_. b i f i d a , C_. andersoni, and C^. e x p l e t a produced three consecutive generations i n the l a b o r a t o r y on t h i s d i e t , and a l l the other species survived without t r o u b l e . Thus t h i s food supply was considered s u f f i c i e n t although the reared specimens always were s l i g h t l y smaller than the f i e l d caught i n s e c t s ( c f . Jansson, 1 9 6 9 ) . Owing to the r a p i d r o t t i n g of excess food i n the c u l t u r e s , continuous v e n t i l a t i o n was r e q u i r e d . This was accomplished by use of a i r stones run o f f the a i r supply to the l a b o r a t o r y . 2. L i f e c y c l e In order to i n v e s t i g a t e how the annual rhythm of s t r i d -u l a t i o n c o r r e l a t e s w i t h the l i f e c y c l e , populations of _C. b i f i d a and C_. e x p l e t a i n s e l e c t e d lakes i n the Southern I n t e r i o r Plateau of B r i t i s h Columbia were studied. Samples were taken at 1-3 weeks i n t e r v a l s between May and October 1 9 6 9 . The lakes studied were: A) C h i l c o t i n , Beeche's P r a i r i e area: East Lake (= Racetrack i n Scudder, 1 9 6 9 a; 1 9 6 9 b ) , Barnes Lake (= Box 4 ) , and Lake Lye (= Box 2 0 - 2 1 ) ; B) Cariboo, Springhouse area: Westwick Lake, Boitano Lake, and Boitano Lake North End; C) Cariboo, Green Timbers Plateau between C l i n t o n and Gang Ranch: Long Lake; D) Kamloops, Lac du Bois area: LB2. The c h a r a c t e r i s t i c s of the lakes are given i n Scudder ( 1 9 6 9 a). Sampling included 1 0 minutes of tape recording i n s i t u , 1 1 a temperature r e c o r d i n g , a 1 0 standard sweep sample ( 1 standard sweep = about one metre long vigorous back: and f o r t h sweep wi t h sweep net at the depth of 2 0 - 3 0 cm, consecutive sweeps were taken by moving slo w l y p a r a l l e l to the shore l i n e ) . Some a d d i t i o n a l a d u l t c o r i x i d s were a l s o c o l l e c t e d . Sampling was done at the same l o c a l i t y i n the lakes each time. Sweep samples were preserved i n 7 0 per cent a l c o h o l , and a d d i t i o n a l a d u l t s were preserved i n a l c o h o l or modified a l c o h o l i c Bouin's f l u i d (Ewen, 1 9 6 2 ) . In a d d i t i o n to recording the temperature at the time of each sample, a i r and water temperatures were continuously recorded at Westwick Lake using a B r i s t o l p o r t a b l e two pen r e c o r d i n g thermometer model 2T 501—1A-1B ( B r i s t o l Co., Waterbury, Conn.). Continuous records of the temperature i n shallow water i n a l l water bodies were a l s o obtained by using Ryan model D-15 waterproof recorders (Ryan Instrument Co., S e a t t l e , Wash.). C o n d u c t i v i t y of water samples was recorded monthly w i t h a Radiometer type CDM 2 d c o n d u c t i v i t y meter (Radiometer Co., Copenhagen, Denmark). From, the standard sweep samples the i d e n t i t y and number of ad u l t s and l a r v a e i n the d i f f e r e n t i n s t a r s were counted and thus the sequence of generations f o r the species was determined. The a d u l t specimens of v a r i o u s species o c c u r r i n g i n the lakes were i d e n t i f i e d according to Hungerford ( 1 9 4 8 ) . The l a r v a e of C_. b i f i d a and C_. e x p l e t a were i d e n t i f i e d according to Scudder ( 1 9 6 6 ) , and the l a r v a e of other species could be separated from Cenocorixa l a r v a e according to some characters common to both a d u l t s and l a r v a e ( c f . Jansson, 1 9 6 9 ) , 12 and a key of Jansson and Scudder ( i n p r e p a r a t i o n ) . In iden-t i f i c a t i o n of a d u l t specimens from samples taken at a time when two generations overlap, the r e l a t i v e age of the specimens was determined according to t h e i r softness and c o l o r : o l d specimens are hard and d a r k l y pigmented while young ones are s o f t and l i g h t l y pigmented. From preserved a d u l t m a t e r i a l the development of gonads was st u d i e d i n the l a b o r a t o r y ; females were examined by opening the abdomen d o r s a l l y and observing the presence or absence of chorionated eggs; a l c o h o l preserved males were studie d by p l a c i n g them i n t o d i s t i l l e d water f o r 6 - l 8 hours and then removing the t e s t e s . Testes were then stained by a method using both a s o l u t i o n of n a t u r a l o r c e i n ( 1 0 - 1 5 minutes) and s y n t h e t i c o r c e i n ( 1 5 - 2 0 minutes) at room temp-erature ( S t r i c k b e r g e r , 1 9 6 2 ) , and f i n a l l y squashed l i g h t l y on a microscope s l i d e w i t h a cover s l i p . In these prepar-a t i o n s the chromatin stained dark purple and the stages of spermatogenesis could e a s i l y be i d e n t i f i e d . The r e s u l t s obtained by using t h i s method were confirmed by making s e r i a l s e c t i o n s of t e s t e s and seminal v e s i c l e s using the m a t e r i a l preserved i n modified a l c o h o l i c Bouin's f l u i d . During the summer of 1 9 7 0 the same sampling methods were a p p l i e d to populations of _C. andersoni and C_. b l a i s d e l l i at the f o l l o w i n g l o c a l i t i e s : A) Washington, Whatcom County, Custer: a g o l f course pond (C_. andersoni); B) B r i t i s h Columbia, Vancouver: semitemporary pond at the corner of 1 6 t h Avenue and Wesbrook Crescent; MacCleery Golf Course: a r t i f i c i a l pond (C^ . b l a i s d e l l i ) . However, the annual rhythm of s t r i d u l a t i o n was t e s t e d i n the l a b o r a t o r y r a t h e r than i n the f i e l d because the populations were not very dense. A l s o the t e s t i s squash..preparations were made from f r e s h r a t h e r than a l c o h o l preserved m a t e r i a l . Temperature recorders could not be used during the summer of 1 9 7 0 * but data on a i r temperatures at Surrey M u n i c i p a l H a l l weather s t a t i o n , B r i t i s h Columbia, were obtained f o r comparison w i t h the a i r temperatures i n the i n t e r i o r . 3. S t r i d u l a t i o n A l l recordings were made w i t h a portable/mains tape recorder (Uher 4000 Report-L), type LC-10 hydrophone ( A t l -a n t i c Research Co., A l e x a n d r i a , Va.), Ampex 34l and 64l tapes (Ampex Co., Redwood C i t y , C a l . ) . Tape speed i n the tape recorder was always 1 9 cm per second except i n the d i e l p e r i o d i c i t y experiments when 2.4 cm per second speed was used. B a t t e r y operation was used only under f i e l d c o n d i t i o n s . Owing to the f a i n t n e s s of the s i g n a l s of some Cenocorixa species, maximum input was always used while r e c o r d i n g . The s i g n a l s were analysed on a sound spectro-graph type 6 7 5 M i s s i l y s e r (Kay E l e c t r i c Co., Pine Brook, N.J.). S e t t i n g s used i n the spectrograph while a n a l y s i n g were as f o l l o w s : input and reproduce VU - 1 . 5 f o r peaks of the s i g n a l s , mark l e v e l 6 . 5, shape f l a t , bandwidth narrow f o r general f i g u r e s of the s i g n a l s and wide f o r d e t a i l e d a n a l y s i s of the pulse s t r u c t u r e . 1 Terminology used i n the d e s c r i p t i o n s of the s i g n a l s i s as f o l l o w s : ( F i g . 1): Impact: sh o r t e s t d i s t i n g u i s h a b l e element of a s i g n a l (can only be seen i n the d e t a i l e d f i g u r e s of pulse s t r u c t u r e This i s not the same as a sound wave, but would appear to be a combination of s e v e r a l sound waves. Pulse: the emission r e s u l t i n g from the passage of the pars s t r i d e n s over the plectrum: a complete c y c l e of the apparatus beginning and ending at the p o s i t i o n of r e s t . This i s the common concept of a pulse i n b i o a c o u s t i c s , which d i f f e r s from the p h y s i c a l d e f i n i t i o n of a pulse. Pulse i n t e r v a l : the i n t e r v a l between two consecutive pulses. Pulse s t r u c t u r e : arrangement of impacts i n a pulse. Pulse group: a d i s t i n c t group of pulses w i t h i n a s i g n a l Pulse group i n t e r v a l : the i n t e r v a l between two pulse groups. In some s i g n a l s t h i s i s c l e a r l y longer than the pulse i n t e r v a l , but i n some cases i t may be almost equal to a pulse i n t e r v a l . However, i n the l a t t e r case there i s a c l e a r d i f f e r e n c e between the pulses of the pulse groups and t h i s defines the l o c a t i o n of the pulse group i n t e r v a l . Pulse r a t e : r e p e t i t i o n r a t e of pulses w i t h i n a sta t e d time (second). Pulse group r a t e : r e p e t i t i o n r a t e of pulse groups w i t h i n a stated time (second). Main frequency area: the frequency range at which the amplitude of the sound i s strongest (appears as the darkest area i n the sound spectrograms). 15 1 SECONDS F i g . 1. Terminology used i n the d e s c r i p t i o n s of the s t r i d -u l a t o r y s i g n a l s . A b s c i s s a : time (seconds); ordinate: frequency ( k i l o c y c l e s per second); I = impact; P = pulse; PG = pulse group; PGI = pulse group i n t e r v a l ; PI = pulse i n t e r v a l ; MF = main frequency area. 16 Temporal p a t t e r n of pulses: arrangement of pulses i n a complete s i g n a l (according to some authors t h i s i s a l s o c a l l e d pulse modulation). S i g n a l or c a l l : a complete set of pulses or pulse groups. Recording of the s t r i d u l a t o r y s i g n a l s was made both i n n a t u r a l h a b i t a t s and i n the l a b o r a t o r y . In the l a b o r a t o r y s a t i s f a c t o r y recordings could be made, p r o v i d i n g that no motors were used i n the same room. The bug container was i s o l a t e d from the general v i b r a t i o n s of the b u i l d i n g by p l a c i n g i t on a 5 cm thick, foam rubber cushion. The problem of p o s s i b l e sound changes i n l a b o r a t o r y c o n d i t i o n s was studied by ana l y s i n g s i g n a l s recorded i n sev e r a l d i f f e r e n t c o n t a i n e r s . Glass, b r i c k , styrofoam, and s e v e r a l d i f f e r e n t p l a s t i c containers were t r i e d and a l l had an e f f e c t of making one or more frequency areas of the sound stronger than others, or c r e a t i n g harmonics. Wooden trays and some s o f t p l a s t i c t r a y s and paper mugs were found to absorb almost a l l sounds thus making the s i g n a l s too f a i n t . The only container where the s i g n a l s were s i m i l a r to those recorded i n n a t u r a l c o n d i t i o n s was a metal cottage bathtub l i n e d i n t e r i o r l y at the sides and bottom w i t h a 5 - 1 0 cm t h i c k l a y e r of f i n e g r a i n sand and with some l a r g e r rocks on the bottom- the best r e s u l t s were obtained when the bugs were s i t t i n g on the rock while s t r i d u l a t i n g . To keep the bugs w i t h i n the area at which the recording could be done s a t i s f a c t o r i l y , a fence made of s o f t p l a s t i c screen was used. 17 The e f f e c t of temperature on s t r i d u l a t i o n was studied by recording i n n a t u r a l c o n d i t i o n s , bathtub, and c u l t u r e t r a y s . I t was shown tha t although the c u l t u r e t r a y s had some e f f e c t on the frequency of the sounds, t h i s d i d not a f f e c t the pulse t a t e , and the tr a y s could be used f o r t h i s study. Low temperatures i n the l a b o r a t o r y were obtained by placinggthe t r a y s i n a constant temperature cabinet at 5°C f o r a few hours, and hi g h temperatures were produced by p l a c i n g a 100 watt lamp above the tr a y s u n t i l the temperature was so high that the bugs d i d not s t r i d u l a t e any more. A f t e r these treatments the temperature was allowed to increase or decrease s l o w l y towards room temperature. The bugs were induced to s t r i d u l a t e at d e s i r e d temperatures by p l a y i n g back to them c e r t a i n s i g n a l s from previous recordings and simultaneously r e c o r d i n g a l l s i g n a l s w i t h another tape recorder. The loudspeaker used f o r these playbacks was a Uher earphone protected from wetting by a t h i n rubber sleeve (condom). Graphs f o r the e f f e c t of temperature on pulse r a t e as w e l l as on pulse group r a t e were p l o t t e d and c a l c u l a t e d by computer ( B i o l o g y Data Centre, I n s t i t u t e of Animal Resource Ecology, U n i v e r s i t y of B r i t i s h Columbia). S t r i d u l a t o r y mechanism and movements in v o l v e d i n the sound production were observed while the bugs responded to playback s i g n a l s . However, because the movements are r e l -a t i v e l y f a s t , s a t i s f a c t o r y observations could be made only at low temperatures (10-15°C). Morphology of the s t r i d u l a t o r y apparatus was studied 18 by a mark. 2 A Cambridge Stereoscan e l e c t r o n microscope (Cambridge, England). S p e c i f i c d i f f e r e n c e s i n the s t r u c t u r e of the pars s t r i d e n s and the plectrum apparently c o r r e l a t e w i t h the loudness of the s i g n a l s of various species ( c f . M i t i s , 1936). However, no s u i t a b l e equipment was available-f o r measuring the amplitude of the s i g n a l s and thus, the study of the morphology of the s t r i d u l a t o r y apparatus was r e s t r i c t e d to the general s t r u c t u r e of the pars s t r i d e n s and the plectrum. The d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of some species was i n v e s t i g a t e d i n the f i e l d . Recordings f o r f i v e minutes i n each hour were c a r r i e d over 24 hour periods during May and June 1969 at Barnes Lake, Westwick Lake, and LB2. Laboratory observations on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y i n a l l species were c a r r i e d out during the s p r i n g and summer of 1970. In these experiments the bugs were placed i n c u l t u r e t r a y s which had been painted grey om the sides and bottom: i n transparent t r a y s the bugs tend to swim f o r hours against the w a l l s . The tr a y s were kept undisturbed i n the l a b o r a t o r y at r e l a t i v e l y constant temperature (20-24°C) and the bugs were placed i n them 24 hours p r i o r to the beginning of each experiment. The l i g h t c o n d i t i o n s were n a t u r a l except that the t r a y s never re c e i v e d d i r e c t s u n l i g h t and the room apparently was always s l i g h t l y darker than i n d i r e c t l i g h t outdoors: no a r t i f i c i a l l i g h t was allowed i n the room during the t e s t s . Recordings were made by connecting the tape recorder to a time c l o c k set such that there was a recording f o r f i v e minutes every hour over the f u l l 24 hour p e r i o d , and the t e s t s were run f o r f i v e consecutive days. The hydrophone was placed i n the middle of the t r a y and the t r a y was p o s i t i o n e d on a foam rubber cushion. 4. Behavior The behavioral r o l e of s t r i d u l a t i o n was i n i t i a l l y studied by observing the bugs i n c u l t u r e t r a y s and i n t h e i r n a t u r a l environment i n shallow water during the summer of 1969. Experimental t e s t s i n the l a b o r a t o r y were c a r r i e d out during the spr i n g and summer of 1970. The most d e t a i l e d a n a l y s i s of the s t r i d u l a t o r y behavior was c a r r i e d out on C_. b i f i d a . The f i r s t experiments followed those of S c h a l l e r (1951) and Finke (1968) by observing and q u a n t i f y i n g a l l a c t i v i t i e s of the experimental specimens under va r i o u s c o n d i t i o n s . However, only one or two specimens were t e s t e d at one time, i n order to avoid p o s s i b l e d i s t -urbing e f f e c t s of l a r g e numbers on each other. For t h i s a n a l y s i s , 200 specimens of C_. b i f i d a were taken from Lake Lye i n l a t e A p r i l 1970 and transported to the l a b o r a t o r y . Because males were s t r i d u l a t i n g and a l s o c o p u l a t i o n attempts were observed, the specimens were thought to be ready f o r the t e s t s . The f o l l o w i n g four c u l t u r e s were ,-s.et u p 3 0 males .20 males and 20 females; 30 females; 1 male. Tests were c a r r i e d out every second day u n t i l the 1 1 t h or 1 3 t h day, and the t e s t p e r i o d f o r each experimental c o n d i t i o n was 15 minutes. The experimental c o n d i t i o n s were: alone, w i t h 2 0 a u d i t o r y , v i s u a l , or chemical s t i m u l i . In order to provide n a t u r a l a u d i t o r y s t i m u l i , a small cage was made of p l a s t i c screen, and 4 - 5 specimens from the 3 0 male c u l t u r e were placed i n t o t h i s cage which then was placed i n t o the t r a y w i t h the experimental animals, i . e . the experimental bugs could hear the s i g n a l s of the specimens i n the cage, but could not touch them. For v i s u a l s t i m u l i , a small waterproof container of transparent p l a s t i c was made and the s t i m u l a t i n g specimen was placed i n t o t h i s container which then was i n t r o d -used to the experimental animals. A l s o a dead pinned specimen was t r i e d , i n t h i s case f i x e d at the end of a gl a s s rod. Chemical stimulus was provided by keeping two males from the 3 0 male c u l t u r e , or two females from the 3 0 female c u l t u r e , , i n a t r a y f o r 3 - 4 hours and removing these specimens j u s t before i n t r o d u c i n g the experimental animals i n t o the t r a y . Results of the experiments were analysed using the Wilcoxon matched-pairs signed-ranks t e s t and Friedman two-way a n a l y s i s of variance ( S i e g e l , 1 9 5 6 ) . When the true response of r e c e p t i v e CJ. b i f i d a females to c o n s p e c i f i c male s i g n a l s was discovered the basis f o r f u r t h e r b e h a v i o r a l stud i e s was to keep males and females of every species i n separate c u l t u r e s thus preventing a l l un-de s i r e d c o p u l a t i o n s . The f u n c t i o n and the s i g n i f i c a n c e of the s t r i d u l a t o r y s i g n a l s was then t e s t e d by p l a y i n g back c o n s p e c i f i c male s i g n a l s to a group of females and the responding females were t r a n s f e r r e d to another t r a y . The response of these females was then tested against a l l 21 p o s s i b l e C o r i x i d a e s i g n a l s , and f i n a l l y some males of t h e i r own species were introduced i n t o the same t r a y and c o p u l a t i o n behavior was observed. A l s o the group of females which did not respond to c o n s p e c i f i c male s i g n a l s was observed i n the presence of some males. By p l a y i n g back p r e v i o u s l y recorded female s i g n a l s the males were induced to t r y to copulate, but the unreceptive females adopted a c e r t a i n r e l e a s e behavior which could then be studied. A f t e r these t e s t s both r e c e p t i v e and unreceptive females were preserved i n a l c o h o l and t h e i r gonad development was examined. Playback experiments u t i l i s i n g a l l p o s s i b l e p r e v i o u s l y recorded s i g n a l s were a l s o c a r r i e d out wi t h males of each species of the genus Cenocorixa. In these experiments the s t r i d u l a t o r y response of va r i o u s males was recorded and observations of t h e i r moving a c t i v i t i e s were made. In the species r e c o g n i t i o n experiments each s i g n a l was played f i v e times to a group of specimens ( u s u a l l y f i v e ) . When a l l d i f f e r e n t s i g n a l s hadebeen played back f i v e times the whole experiment was repeated f i v e times (thus t o t a l playback f o r each s i g n a l was 25 times). When specimens were t e s t e d against various s i g n a l s , the bugs were allowed f i v e seconds i n which to answer, f o r a p o s i t i v e r e a c t i o n . Another f i v e seconds was allowed to elapse before repeating the playback, but i f the t e s t animals s t r i d u l a t e d during t h i s l a t t e r f i v e second p e r i o d , the s i g n a l was not considered to be a response to the playback, and a f u r t h e r f i v e seconds was allowed to elapse before the next playback. A l l of these experiments were made at room temperature (21-24°C). 22 In a l l playback, experiments the loudness of the s i g n a l s was adjusted to be as n a t u r a l as p o s s i b l e . The volume of the tape recorder p l a y i n g the s i g n a l s back was adjusted by recor d i n g w i t h another tape recorder through the hydrophone. These experiments were c a r r i e d out i n the c u l t u r e t r a y s , using the earphone as a loudspeaker. However, owing to echoes i n the tr a y s the experiments on the distance f o r r e c o g n i t i o n of s i g n a l s of the opposite sex were c a r r i e d out i n the sand l i n e d bathtub, using an underwater loud-speaker model MM-2PPS ( U n i v e r s i t y Sound Co., Oklahoma C i t y , Okla.). The r e s u l t s of t h i s experiment were confirmed w i t h some of the species by p l a c i n g males and females i n separate small cages made of p l a s t i c screen, and observing t h e i r responses to each other's s i g n a l s at va r i o u s d i s t a n c e s . The d e t a i l e d observations on a g o n i s t i c behavior between males were a l s o made i n the bathtub. 23 I I I . RESULTS 1. Mechanism of sound production and morphology of the s t r i d u l a t o r y apparatus In the genus Cenocorixa both males and females are able to s t r i d u l a t e . Three d i f f e r e n t mechanisms of sound production were observed: i ) By rubbing a s e r i e s of s p e c i a l s t r i d u l a t o r y pegs (pars s t r i d e n s ) , l o c a t e d a n t e r o b a s a l l y on the fore femora ( F i g . 2 ) , against the edge of the max-i l l a r y p l a t e (plectrum), l o c a t e d j u s t p o s t e r i o r l y to the d o r s o l a t e r a l corner of the anteclypeus (terminology according to Parsons, 19^5] 1 9 6 6 ) ( F i g . 3 ) . i i ) By rubbing the hind le g s a l t e r n a t e l y or together against the f o l d e d f o r e wings l y i n g above the abdomen, or against the v e n t r a l side of abdomen and e x t e r n a l g e n i t a l i a . i i i ) In two species f a i n t s t r i d u l a t o r y sounds were recorded at the beginning of s u c c e s s f u l c o p u l a t i o n , but the o r i g i n of these sounds could not be detected. The f i r s t category Is c l e a r l y true s i g n a l l i n g i n that the movement i s made s p e c i f i c a l l y f o r sound production. The second category seems to belong to sounds produced as a by-product of some a c t i v i t y , the prime a c t i o n of which i s not sound production, but one of c l e a n i n g or the l i k e . The t h i r d category might be j u s t sound produced as a r e s u l t of f r i c t i o n between the two specimens, but a l t e r n a t i v e l y i t might as w e l l be an important signal.'^for a s u c c e s s f u l c o p u l a t i o n . However, i t cannot be c l a s s i f i e d owing to the f a c t that the source of the sound i s unknown. 24 F i g . 2. Stereoscan photograph of the f r o n t l e g of _6. b l a i s -d e l l i male showing the l o c a t i o n of the pars s t r i d e n s ( p s ). •Magnification xlOO. F i g . 3- Stereoscan photograph of the head of C. b l a i s d e l l i female showing the l o c a t i o n of the plectrum (p). Fronto-l a t e r a l view, m a g n i f i c a t i o n x50. 26 The true s t r i d u l a t o r y s i g n a l s i n the f i r s t category c o n s i s t of a s e r i e s of pulses, each pulse being a forward push of one l e g . When the l e g i s moved backwards i t does not touch the plectrum. However, u s u a l l y the other l e g i s pushed forwards at the same time, i . e . every second pulse i s produced by one l e g . The a l t e r n a t e movement,"of the f r o n t legs was the only way that both males and females were observed to produce these s i g n a l s , regardless of the pulse r a t e or the temporal p a t t e r n of pulses -in the s i g n a l s . The study of the morphology of the s t r i d u l a t o r y apparatus showed that g e n e r a l l y the males have more pegs and t h i c k e r pegs on the pars s t r i d e n s than the females (Table I, F i g . 4). A l s o the s i z e of the plectrum i s d i f f e r e n t i n the two sexes: the m a x i l l a r y p l a t e of the males i s g e n e r a l l y l a r g e r than that of the females ( F i g . 4). Although no equipment was a v a i l a b l e f o r a c t u a l meas-^ urement of the loudness of the s i g n a l s , s u b j e c t i v e observ-a t i o n s i n d i c a t e c l e a r d i f f e r e n c e s between the species. In a d d i t i o n , i n each species the male c a l l always appears louder than the female c a l l . A c o r r e l a t i o n i s suggested between the loudness of the s i g n a l s and the thickness of the pegs of the pars s t r i d e n s . However, the s t r u c t u r e of the pars s t r i d e n s may not be the only f a c t o r a f f e c t i n g the amplitude of the sound: the s i z e of the plectrum was a l s o observed to be d i f f e r e n t i n the two sexes.. 2 7 Table I. Thickness of the pegs of the pars s t r i d e n s (average from 1 0 specimens)- and comparison of the number of peg rows on the pars s t r i d e n s ( 1 0 specimens) and the number of impacts per pulse (mean + standard e r r o r ; number of specimens as i n Table I I ) . In s e v e r a l species the males are able to produce "slow" and " f a s t " pulses i n t h e i r s i g n a l s : the number of im-pacts per pulse i n these d i f f e r e n t pulses are i n d i c a t e d by s and f , r e s p e c t i v e l y . * - no s i g n a l s recorded. The order of the species i s according to data contained In Appendix I. Species/sex b i f i d a o* b i f i d a ? k u i t e r t i o* k u i t e r t i ? andersoni o* andersoni ? utahensis o* utahensis $ dakotensis o* dakotensis $ b l a i s d e l l i o* b l a i s d e l l i $ wileyae o* wileyae ? e x p l e t a o* e x p l e t a ? pars s t r i d e n s , thickness of pegs (mm) . 0 0 5 6 . 0040 . 0 0 4 6 . 0 0 1 8 . 0 0 6 5 . 0 0 2 9 . OO58 . 0 0 2 1 .OO59 . 0 0 2 9 . 0 0 8 1 . 0 0 3 0 . 0 0 6 2 . 0 0 3 3 . 0 0 9 3 . 0 0 5 0 Number of peg rows on pars s t r i d e n s . 1 5 - 1 8 8-12 1 3 - 1 5 6- 9 1 0 - 1 3 7- 9 1 1 - 1 4 8-12 1 1 - 14 8- 1 2 1 3 - 1 5 9- 1 2 1 5 - 1 7 1 2 - 1 6 Number of impacts per pulse 9 . 0 4 + 0.29 6 . 6 4 + 0.30 s 7.58 + 0.18 f 4.35 ± 0.13 s 4.56 + 0 . 1 4 f 3.27 + 0.08 1.68 + 0.06 s 5.56 + 0.18 f 2 . 8 8 + 0.09 4.63 + 0 . 1 4 8.08 + 0 . 3 1 5. 3 9 + 0.22 s 8.05 + 0 . 2 4 f 4.82 + 0.18 7.92 + 0.23 slO.72 + 0.35 f 3.96 + 0 . 1 4 6.97 + 0.30 6.26 + 0.18 7.0 5 + 0.22 1 0 - 1 2 7- 8 28 F i g . 4 . Stereoscan photographs of the s t r i d u l a t o r y apparatus of £. b l a i s d e l l i . A = male plectrum; B * male pars s t r i d e n s , pegs; C = female plectrum; D = female pars s t r i d e n s , pegs. M a g n i f i c a t i o n s : plectrum x 2 0 0 , pars s t r i d e n s xlOOO. 2. Audiospectrographic a n a l y s i s of the s t r i d u l a t o r y s i g n a l s a) General The s t r i d u l a t o r y s i g n a l s of the various species of Cenocorixa. are species s p e c i f i c . The most constant character i s the temporal p a t t e r n of pulses. Further s p e c i f i c d i f f -erences are found i n the s t r u c t u r e of pulses, i n the pulse r a t e , and i n the s i g n a l l e n g t h . The s i g n a l s of the two sexes are a l s o d i f f e r e n t . Cenocorixa females are able to produce only .one kind of s i g n a l per species, while i n the males of s e v e r a l species the s i g n a l i s composed of two d i s t i n c t l y d i f f e r e n t p a r t s . J i n some cases'Jthese p a r t s can be produced separately; these males are thus able to produce two d i f f e r e n t s i g n a l s . In the s t r i d u l a t i o n the s i g n a l s are composed of s e v e r a l p u l s e s , and f u r t h e r , each pulse c o n s i s t s of s e v e r a l impacts. Thus the sound i s not continuous, but even w i t h i n the pulses i t i s b u i l t up of short c y c l e s each followed by a short i n t e r v a l . Length of the i n t e r v a l s between two consecutive impacts vary between the species and between d i f f e r e n t p a r ts of the s i g n a l s , and i n some cases even w i t h i n a s i n g l e pulse. I t i s a l s o a f f e c t e d by temperature: the higher the temperature the shorter the i n t e r v a l . This c l e a r l y c o r r e l a t e s w i t h the speed used to draw the pars s t r i d e n s over the plectrum, and thus i t i s apparent that each impact represents a s t r i k e of one peg row of the pars s t r i d e n s on the plectrum. However, the number of peg rows of the pars s t r i d e n s i s always more than the average number of impacts per pulse (Table I t ) : the bugs do not seem to use the whole pars s t r i d e n s i n producing 30 the sounds. Table I I records the main frequency areas, average numbers of pulses per s i g n a l s , and the numbers of pulse groups per s i g n a l s i n the var i o u s species. From these data the f o l l o w i n g g e n e r a l i z a t i o n s can be made: i ) The frequency of the sound i s approximately the same i n a l l species and sexes. i i ) Female s i g n a l s u s u a l l y i n c l u d e more pulses per c a l l than comparable male s i g n a l s and consequently, the du r a t i o n of the female s i g n a l s i s u s u a l l y longer than that of the male s i g n a l s . i i i ) The male s i g n a l s are u s u a l l y more complicated than the comparable female s i g n a l s . Concerning the numbers of i n d i v i d u a l s used and the numbers of s i g n a l s analysed f o r the i n f o r m a t i o n i n the Table I I , i t should be noted that recordings were made when a number of i n d i v i d u a l s was i n a c u l t u r e t r a y or i n the sand l i n e d bathtub, but i t i s not known how many s i g n a l s from each i n d i v i d u a l was analysed. However, each i n d i v i d u a l was t e s t e d p r i o r to the recordings so that a l l i n s e c t s were known to be i n normal s t r i d u l a t o r y c o n d i t i o n . This experimental procedure i s considered meaningful, since the s i g n i f i c a n c e of s t r i d u l a t i o n concerns more the species than the i n d i v i d u a l s , i . e . the s i g n a l s are species s p e c i f i c , but not i n d i v i d u a l l y d i f f e r e n t . 31 Table I I . Numerical c h a r a c t e r i s t i c s of Cenocorixa signals. Symbols: * = signal composed of one pulse group (number of pulses per pulse group = number of pulses per signal); $ = a l l pulse groups are s i m i l a r ,(sub-sequent groups,. = the f i r s t group). J Species/sex Number of Number of Main Average number Number of Number of pulses per pulse group specimens signals frequency of pulses/signal pulse groups area + standard error per signal F i r s t group (kc/sec) present at analysed recording Subsequent groups b i f i d a d* b i f i d a ? 10 5 75 36 3-4.5 3-4.5 19-57 + 0.59 21.92 + 0.87 1 1 k u i t e r t i 0* 10 72 3-4 . 5 15.03 + O.56 11.20+1.33 13.27+1.11 andersoni o* 10 andersoni ? 3 utahensis o* 3 utahensis $ 2 52 20 34 19 3- 5 4- 5 3-5 3-5 3 0.08 + 1.36 51.63 + 4.13 85.26 + 3 . 3 ^ 1 0 0 . 2 1 + 3 . 4 0 1.75 + 0 . 1 4 2 1 9.19 + 0.89 20.81 + 1.33 28.85 + 1.11 * 4 6.50 + 3 . 6 6 38.79 + 1 - 6 8 dakotensis 0* 10 dakotensis $ 4 52 30 4-5 3-5 23.83 + 0.81 21.89 + 1.85 1 i * b l a i s d e l l i cf 10 b l a i s d e l l i ? 4 37 30 4-5 3-5 17.75 ± 1.42 28.70 + 1.94. 5.62 + 0.^2 , 13.08 + 1 . 2 4 1.00 +0.00 1 ' • * • . * wileyae 0* wileyae ? 10. 5 32 4 1 3.5-5 3-4 36.03 + 1.07 52.66 + 3.71 9.25 + 0.30 1 9 . 4 2 + 0 . 4 5 2.5.5 + 0.03 expleta o* expleta ? 10 3 38 1 4 3-5 . 2.5-3.5 28.05 + 1.52 6 4 . 4 3 + 8 . 6 3 6 . 4 1 + 0.30 8.85- + 1.28 9 . 8 4 + 0.72 7.28 + 0 . 4 8 4 . 4 7 + 0 . 2 4 32 b) D e s c r i p t i o n of the s i g n a l s C_. b i f i d a (Hungerford) ( F i g . 5): Male c a l l : Recorded between 8.0 - 28.8°C. In the experimental c o n d i t i o n s no s i g n a l s were obtained at 7.0°C or below, or at 30.0°C or above. The s i g n a l i s of simple m u l t i p u l s a t e type w i t h c l e a r and even pulse i n t e r v a l s * . Female c a l l : Recorded at 21.0 - 24.7°C only, but tem-perature l i m i t s f o r females to produce s i g n a l s are probably the same as f o r males. The s i g n a l i s very much l i k e t hat of the.male, but w i t h fewer impacts per pulse and much lower amplitude*. C_. k u i t e r t i Hungerford ( F i g . 6): Male c a l l : Recorded between 15.0 - 28.0°C, but i t i s probable t h a t the lower l i m i t f o r s t r i d u l a t i o n of t h i s species i s below 15.0°C. The s i g n a l of _C. k u i t e r t i male i s more com-p l i c a t e d than t h a t of C_. b i f i d a , and two d i f f e r e n t pulse groups were observed: i ) a group of "slow" pulses which ree-semble the c a l l of C_. b i f i d a , but the pulses f o l l o w each oj'her with very short pulse i n t e r v a l s and thus are almost fused together, and i i ) a group of " f a s t " pulses i n which the pulses are much shorter than the slow pulses, but f o l l o w each other w i t h more or l e s s i r r e g u l a r , but d i s t i n c t i n t e r v a l s . S t r u c t u r a l l y the f a s t pulses i n c l u d e l e s s impacts than the slow ones*. The s i g n a l may be composed of slow pulses alone, or both types together. I f i t i s composed of both types the slow pulses are always i n the beginning. The t r a n s i t i o n from * Numerical data on s i g n a l s of each species are i n Tables I and I I . 33 the slow pulses to the f a s t ones i s u s u a l l y gradual. Female c a l l : Never recorded s a t i s f a c t o r i l y . O c c a s i o n a l l y the bugs were observed to perform s t r i d u l a t o r y movements w i t h t h e i r f r o n t l e g s , but apparently the amplitude of these s i g n a l s was too low f o r the equipment used. According to the s t r i d u l a t o r y movements the s i g n a l s probably are of simple m u l t i p u l s a t e type. C_. andersoni Hungerford ( F i g . 7 ) ' Male c a l l : Recorded between 12.0 - 28.0°C, but the lower l i m i t may be below the observed one. U s u a l l y the s i g n a l i s composed of two pulse groups ( l i k e t h a t of _C. k u i t e r t i ) : a slow p u l s a t e d beginning and f a s t pulsated end. Sometimes the f i r s t pulse group i s produced alone. Pulses of the f i r s t group are somewhat i r r e g u l a r and w i t h short i n t e r v a l s , but the pulses of the second group are r e g u l a r and w i t h d i s t i n c t i n t e r v a l s . The t r a n s i t i o n from the slow pulses to the f a s t ones i s abrupt. Female c a l l : Recorded between 21.5 - 26.2°C, but tem-perature l i m i t s are probably the same f o r both sexes. The s i g n a l i s composed of 1-3 simple m u l t i p u l s a t e , somewhat i r r e g u l a r pulse groups. The pulse group i n t e r v a l s were always 1-2 seconds and d i d not seem to be a f f e c t e d by tem-perature. Pulse i n t e r v a l s are d i s t i n c t and the number of impacts per pulse i n _C. andersoni female i s l e s s than i n any other species. 34 C_. utahensis (Hungerford) ( F i g . 8): Male c a l l : Recorded between 11.7 - 28.0°C. To the human ear t h i s c a l l sounds very much l i k e the c a l l of C_. andersoni male, but both the slow and the f a s t pulse groups are con-s i d e r a b l y longer i n _C. utahensis. The spectrogram a l s o shows th a t the pulses of the slow pulse group are not a l l s i m i l a r , but approximately every second pulse i s s h o r t e r i n d u r a t i o n (almost l i k e the pulses of the f a s t pulse group). In _C. utah- ensis , as i n C. andersoni, the slow pulse group may be prod-uced alone. In a complete s i g n a l the t r a n s i t i o n from the slow pulses to the f a s t ones i s abrupt. Female c a l l : Recorded between 21.5 - 23.4°C, but tem-perature l i m i t s are probably the same as f o r the opposite sex. The s i g n a l i s somewhat i r r e g u l a r being a simple m u l t i -p u l s a t e c a l l w i t h d i s t i n c t pulse i n t e r v a l s . C_. dakotensis (Hungerford) ( F i g . 9 ) : Male c a l l : Recorded between 15.0 - 27.4°C. The s i g n a l i s composed of g r a d u a l l y changing pulses: at the very beginning the pulses are r e l a t i v e l y long and without c l e a r i n t e r v a l s , but towards the end of the s i g n a l the pulses become shorter and the pulse i n t e r v a l s become longer. The very f i r s t pulses c o n t a i n more impacts than there are peg rows i n the pars s t r i d e n s : i t i s probable that these pulses are produced by back and f o r t h movement of the pars s t r i d e n s so that the s t r i d u l a t o r y pegs touch the plectrum when the f r o n t l e g i s drawn backwards and when i t i s pushed forwards, while i n .other pulses the sound i s produced 3 5 only when the l e g i s pushed forwards. Female c a l l : Recorded between 20.0 - 24.9°C, but probably produced i n same temperature range as the male c a l l . The s i g n a l resembles very much the male c a l l , but has almost even pulse r a t e throughout the s i g n a l , and the very f i r s t pulses c o n t a i n l e s s impacts than the subsequent pulses. _C. b l a i s d e l l i (Hungerford) ( F i g . 10): Male c a l l : Recorded between 7.0 - 28.8°C. The s i g n a l i s composed of two d i f f e r e n t p a r t s , both of which may be produced completely independently from each other, but which u s u a l l y are produced as f o l l o w s : a simple m u l t i p u l s a t e pulse group w i t h somewhat i r r e g u l a r pulse i n t e r v a l s , followed by s i n g l e , very f a s t pulses w i t h c o n s i d e r a b l y long and o f t e n i r r e g u l a r i n t e r v a l s . This second part i s henceforth con-sidered to be composed of "unipulsated pulse groups" ( c f . _C. wileyae and _C. e x p l e t a ) . Female c a l l : Recorded between 22.2 - 27.2°C. The s i g n a l resembles very much the C_. b i f i d a c a l l . However, only p a r t of the _C. b l a i s d e l l i female c a l l i s composed of r e g u l a r l y repeated p u l s e s , p a r t of i t being more or l e s s i r r e g u l a r . Mounting s i g n a l ' ( F i g . 11): An odd s t r i d u l a t o r y s i g n a l was observed always during the f i r s t few seconds of a s u c c e s s f u l c o p u l a t i o n . O r i g i n of the sound i s unknown. At 22.8°C t h i s s i g n a l was composed of s i x somewhat i r r e g u l a r pulse groups and the whole s i g n a l l a s t e d about f i v e seconds (the c o p u l a t i o n l a s t e d much longer, but no sounds were recorded a f t e r the f i r s t f i v e seconds). The main frequency-area seems to be about 3-5 kc/sec (recording made i n a c u l t u r e t r a y ) . Pulse r a t e i s about 2 4 pulses per second at 22.8°C; t h i s i s n e a r l y twice the pulse r a t e of the f i r s t pulse group of the normal male c a l l , or a female c a l l . _C. wileyae (Hungerford) ( F i g . 1 2 ) : Male c a l l : Recorded between 5 . ^ - 28.2°C. The s i g n a l i s u s u a l l y composed of two p a r t s : f i r s t a simple m u l t i p u l -sate pulse group w i t h slow pulses and short or n o n - e x i s t i n g pulse i n t e r v a l s , then s e v e r a l very short groups of f a s t pulses w i t h c l e a r pulse i n t e r v a l s and r e g u l a r pulse group i n t e r v a l s . O c c a s i o n a l l y one part of the s i g n a l i s produced alone. Female c a l l : Recorded between 1 3 . 6 - 22.9°C, but tem-perature l i m i t s are probably c l o s e r to the male l i m i t s . The s i g n a l i s very r e g u l a r and a simple m u l t i p u l s a t e c a l l w i t h d i s t i n c t pulse i n t e r v a l s . _C. expleta. (Uhler) ( F i g . 1 3 ) : Male c a l l : Recorded between 8.0 - 31.0°C. The s i g n a l i s composed of s e v e r a l pulse groups, the f i r s t one being the f a i n t e s t i n amplitude and wit h the slowest pulse r a t e , the subsequent pulse groups are louder and wit h f a s t e r pulse r a t e , i . e . the whole s i g n a l a c c e l e r a t e s i n both amp-l i t u d e and pulse r a t e . The pulse i n t e r v a l s are d i s t i n c t , but sometimes more or l e s s i r r e g u l a r , and the pulse group i n t e r v a l s are somewhat i r r e g u l a r . Female c a l l : Recorded between 22.4 - 22.8 C only, but temperature l i m i t s are probably the same as i n the opposite sex. The s i g n a l i s composed of d i s t i n c t l y separate pulses arranged i n s e v e r a l pulse groups, thus resembling the male c a l l . However, the female s i g n a l i s much lower i n amplitude and longer i n d u r a t i o n than the male s i g n a l , and i t does not a c c e l e r a t e i n amplitude or i n pulse r a t e . Mounting s i g n a l : During the f i r s t few seconds of s u c c e s s f u l c opulations some f a i n t s t r i d u l a t o r y s i g n a l s were observed. However, no s a t i s f a c t o r y recordings were obtained since the amplitude of these sounds was too low f o r the equipment used. To the human ear the s i g n a l s sounded very much l i k e the mounting s i g n a l s of C_. b l a i s -d e l l i . 38 a F i g . 5. Sound spectrograms of C_. b i f i d a s i g n a l s . A = male s i g n a l ; B = female s i g n a l ; C = d e t a i l s of male s i g n a l (pulses 10-15 i n A); D = d e t a i l s of female s i g n a l (pulses 7-11 i n B). Recorded at 21.3°C. Specimens from B r i t i s h Columbia, C h i l c o t i n , Beeche 1s P r a i r i e , Lake Lye. F i g . 6. Sound spectrograms of _C. k u i t e r t i s i g n a l s . A = male s i g n a l w i t h slow pulses alone; B = complete male s i g n a l ; C = a male s i g n a l w i t h second p a r t dominating; D = d e t a i l s of male s i g n a l (pulses of A). Recorded at 21.9°C. Specimens from C a l i f o r n i a , Tuolumne Co., Tioga Pas s. K I L O C Y C L E S S E C O N D W O W w Cn H> W W CO H O O D CO N H N 'Mr co H O . o » z d co N H K I L O C Y C L E S S E C O N D W O W o w W P-» W W W "•>li.. I OH co 3 9 a F i g . 7- Sound spectrograms of C_. andersoni s i g n a l s . A = complete male s i g n a l ; B = male s i g n a l w i t h slow pulses alone; C = female s i g n a l ; D = d e t a i l s of male s i g n a l (from the middle of A); E = d e t a i l s of female s i g n a l ( from the middle of the f i r s t pulse group i n C). Recorded at 22.4°C. Specimens.from Washington, Whatcom Co., Custer. F i g . 8. Sound spectrograms of C_. utahensis s i g n a l s . A = complete male s i g n a l (a male s i g n a l w i t h the slow pulses alone i s s i m i l a r to the f i r s t pulse group of the complete s i g n a l ) ; B = female s i g n a l ; C = d e t a i l s of male s i g n a l (end of the f i r s t and beginning of the 'second pulse group'in A); D = d e t a i l s of female s i g n a l (pulses 9 - l 8 °f B). Recorded at 22.1°C. Specimens from A l b e r t a , Medicine Hat. 39 b O l -'O u H 5-| w 3 g 1 o o i-J 1 5 -M w — r -2 D lO 5 -•mi- i in <i ill i | M M E l I I •6 -8 S E C O N D S 12 14 5-3 liiiiiiHiilf^ 'liiiiillii p i-& o u CC B ta .> 'S 8 1 ;o • J 15 IH 10-2 •!!!!> i! ' '|1 Nil Hi i i<l •4 •6 -8 1:0 S E C O N D S 1-2 14 8 40 a F i g . 9 - Sound spectrograms of C_. dakotensis s i g n a l s . A = male s i g n a l ; B = female s i g n a l ; C = d e t a i l s of male s i g n a l (pulses 4 - 1 2 of A); D = d e t a i l s of female s i g n a l (pulses 1 -3 and 7 of B). Recorded at 2 1 . 0 °C. Specimens from A l b e r t a , Brooks. F i g . 1 0 . Sound spectrograms of _C. b l a i s d e l l i s i g n a l s . A = male s i g n a l (note the u n i p u l s a t e ' c l i c k s ' a f t e r the mult.ipulsate beginning); B = female s i g n a l ; C = d e t a i l s of male s i g n a l (pulses 5 - 7 of the f i r s t pulse group and the f i r s t ' c l i c k ! of A); D = d e t a i l s of female s i g n a l (pulses 6 - 1 3 of B). Recorded at 2 2 . 4°C. Specimens from B r i t i s h Columbia, Vancouver, Po i n t Grey. as" co M O O ci-SS d co K I L O C Y C L E S , S E C O N D W O W ^ CO W i - C O W 10-CO- ' •- - CO-CD N CO M o g db d co K I L O C Y C L E S S E C O N D W O W CO W i-> CO W v f l f e . . see co- C0--t=r o !«3 8 l I ' 5" SECONDS F i g . 11. Sound spectrogram of CJ. b l a i s d e l l i mounting s i g n a l . The s i g n a l was recorded during the f i r s t few seconds of a s u c c e s s f u l c o p u l a t i o n at 22.8 °C. The f i r s t two pulses at the l e f t are the l a s t pulses of female s i g n a l , then one unipulsate 'click.' of the male, and the sounds produced during the copu-l a t i o n begin j u s t before the one second mark. Specimens from B r i t i s h Columbia, Vancouver, Point Grey. 4=-H 42 a F i g . 12. Sound spectrograms of C_. wileyae s i g n a l s . A = male s i g n a l ; B = female s i g n a l ; C = d e t a i l s of male s i g n a l (the f i r s t and the t h i r d pulse group of A); D = d e t a i l s of female s i g n a l (part of B from the middle of the s i g n a l ) . Recorded at 21 .9 °C. Specimens from C a l i f o r n i a , Lassen Co., Said Lake. F i g . 13- Sound spectrograms of C_. e x p l e t a s i g n a l s . A = male s i g n a l ; B = female s i g n a l (only p a r t of the s i g n a l i s shown: whole s i g n a l i n c l u d e d seven pulse groups); C = d e t a i l s of male s i g n a l ( t h i r d pulse group of A); D = d e t a i l s of female s i g n a l (the l a s t four pulses of the second pulse group i n B). Recorded at 22.3 °C. Specimens (from B r i t i s h Columbia, Kamloops (LB2). K I L O C Y C L E S , S E C O N D 12.. am. Ml. 09 H O g db O CO (0 K I L O C Y C L E S ^ S E C O N D cn o St K i Cn H> I .1 I lo-co-r*.VM.,-. 43 c) E f f e c t of temperature on s t r i d u l a t i o n In C o r i x i d a e , as i n a l l p o i k i l o t h e r m s , temperature a f f e c t s a l l body a c t i v i t i e s , i n c l u d i n g speed of movements; upper and lower l i m i t s on the body f u n c t i o n s a l s o e x i s t . Since s t r i d u l a t i o n i s produced by movements of the f r o n t l e g s , i t i s a f f e c t e d by temperature. However, the temporal p a t t e r n of pulses and the number of pulses per s i g n a l are constant i n each species regardless of temperature (except i n some cases c l o s e to temperature extremes). Thus, the parameters a f f e c t e d by temperature are the d u r a t i o n of the s i g n a l s and the pulse r a t e i n the s i g n a l s . The only species where the change i n temperature changed the temporal p a t t e r n of pulses was C_. utahensis, and t h i s occurred at temperature extremes: above 27.5°C and below 13.0°C the specimens t e s t e d were able to produce only slow pu l s e s , i . e . f a s t s t r i d u l a t i o n was i n h i b i t e d . The normal s i g n a l of t h i s species i s composed of both a slow pulse group and a f a s t pulse group. F i g s . 14-16 show the average d u r a t i o n of the s i g n a l s i n v a r i o u s species at d i f f e r e n t temperatures. I t i s seen that the curve w i t h s i g n a l l e n g t h p l o t t e d against temperature has a h y p e r b o l i c shape. Departures from t h i s were observed only when s t r i d u l a t i o n was recorded c l o s e to the temperature extremes ( F i g . 16: C_. wileyae s i g n a l s at the lowest tem-perature and C. e x p l e t a s i g n a l s at the highest temperatures). A graph w i t h increase In pulse r a t e p l o t t e d against temperature forms a s t r a i g h t l i n e ( l i n e a r r e gression) ( F i g s . 17-26). In cases where a s i g n a l i s composed of pulse groups the temperature a f f e c t s both the pulse r a t e w i t h i n t h pulse groups ( F i g s . 24 and 2 6 ) and the r e p e t i t i o n r a t of the pulse groups ( F i g s . 2 7 - 2 9 ) . 4 5 8n To 20 30 Temperature (°C) F i g . 14. E f f e c t of temperature on s i g n a l d u r a t i o n i n £. b i f i d a (A), C_. k u i t e r t i (B), and C_. andersoni (C). Symbols: closed c i r c l e s = male s i g n a l s ; open c i r c l e s = female s i g n a l s . Standard er r o r s i n d i c a t e d by v e r t i c a l l i n e s ( l e s s than 0.1 second standard e r r o r f a l l s w i t h i n the s i g n of the symbol used). Curves f i t t e d by eye only on male s i g n a l s . 4 6 n 1 1 10 20 30 T e m p e r a t u r e (°C) F i g . 15. E f f e c t of temperature on s i g n a l d u r a t i o n i n CJ. u t a -hensis (A), CJ. dakotensis (B), and (J_. b l a i s d e l l i (C). In CJ. b l a i s d e l l i male s i g n a l s only the f i r s t pulse group of the s i g n a l s i s concerned. Symbols as i n F i g . 1 4 . Kl a F i g . 1 6 . E f f e c t of temperature on s i g n a l d u r a t i o n i n C. wileyae (A) and CJ. e x p l e t a (B). Symbols as i n F i g . 1 4 . 48 25-0_ 20»0 15-0 10-01 5-0 U 0-0 UJ o.o \ LLI in ^ 20»0 CL 1 5 . 0 1 10.0 5»0 0«0 -0-7G5B + 0 4 G G 3 X 5.0 10» 0 15»0 20»0 Y = - 1 2 - 5 3 7 G + 0-9539X N = 7 8 25-0 30»0 N = 3G O'O 5.0 10«0 15«0 20»0 25»0 T E M P E R A T U R E ( ° C ) 30.0 F i g . 17. E f f e c t of temperature on pulse r a t e i n C_. b i f i d a s i g n a l s . A = male s i g n a l s ; B = female s i g n a l s . Specimens from B r i t i s h Columbia, C h i l c o t i n , Beeche's P r a i r i e , Lake Lye. 4 9 5 0 » 0 ^ . 4 5 » 0 4 0 » 0 3 5 » 0 _ . U LLI ^ 3 0 * 0 1 LD 2 5 » 0 Ll LD LL 1 5 . 0 1 1 0 . 0 . . 5 . O . . 0 « 0 . Y = -7°9G27 + Y •= -0-9917 + 1-5535X 0-7934X N = 1 5 N = 0.0 5.0 1 0 . 0 1 5 . 0 2 0 . 0 2 5 » 0 T E M P E R A T U R E ( ° C ) 3 0 » 0 F i g . 18. E f f e c t of temperature on pulse r a t e i n C_. k u i t e r t i male s i g n a l s . Symbols: t r i a n g l e = f i r s t pulse group of the s i g n a l ; X.= second pulse group of the s i g n a l . Specimens from C a l i f o r n i a , Tuolumne Co., Tioga Pass. 5 0 0-0 5 - 0 . 1 0 - 0 1 5 - 0 EO-0 E 5 - 0 3 0 * 0 T E M P E R A T U R E C°C) F i g . 1 9 . E f f e c t of temperature on pulse r a t e i n C. andersoni male s i g n a l s . Symbols as i n F i g . 1 8 . Specimens from-Washing-ton, Whatcom Co., Custer. 2 5 - 0 2 0 » 0 5 - 4 0 2 3 + 0-G3G5X 1 0 » 0 1 5 . 0 2 0 . 0 \ 4 - 1 9 1 5 + 1 - 0 2 4 0 X 5 1 N = 3 5 2 5 . 0 0 - 0 5-0 10 -0 1 5 » 0 2 0 « 0 2 5 . 0 T E M P E R A T U R E C°C) 3 0 » 0 30« 0 F i g . 20. E f f e c t of temperature on pulse r a t e i n _C. andersoni (A) and C_. utahensis (B) female s i g n a l s . Specimens of C. an-dersoni from Washington, Whatcom Co., Custer and C_. utahensis from A l b e r t a , Medicine Hat. 5 2 55*0 + 50» 0. 45.01 40*0 1 35*0 U . UJ ^ 30-01 Dl 25»0 UJ LD Y - - 1 3 ° 4 7 2 G + 2 ° 1 0 3 5 X Y = - 5 • 9 2 9 1 + 1-2253X N = 2 4 N = 4 1 o-o 5.0 10-0 15-0 E0«0 E5-0 30.0 T E M P E R A T U R E ( ° D F i g . 2 1 . E f f e c t of temperature on pulse r a t e i n C_. utahensis male s i g n a l s . Symbols as i n F i g . 1 8 . Specimens from Washing-ton, F r a n k l i n Co., Scootenay Re s e r v o i r and Mesa.. 5 3 5 0 » 0 Y = - 3 - 7 4 2 4 + 0-G849X N = 5 2 1 5 ^ 0 1 0 . 0 1 \ L D . [jj E 5 - 0 . _J 0_ 5 0 . 0 1 1 5 . 0 1 1 0 . 0 1 0-0 5 » 0 1 0 . 0 1 5 . 0 5 0 » 0 5 5 » 0 3 0 » 0 Y = - 1 8 - 2 5 5 3 + 1-2857X N = - 2 7 5-0 0.0 O'O 5-0 1 0 . 0 1 5 . 0 5 0 » 0 5 5 . 0 T E M P E R A T U R E ( ° C ) 3 0 « 0 F i g . 22. E f f e c t of temperature on pulse r a t e i n _C. dakotensis s i g n a l s . A = male s i g n a l s ; B = female s i g n a l s . Specimens from A l b e r t a , Brooks. 54 E 5 - 0 - . Y-= - 7 ° 9 7 4 0 + 0 - 8 5 4 3 X 1 5 » 0 1 0 « 0 ± 5 « 0 0.0 5 o 4 2 3 1 + 0 2 3 4 G X N - 2 4 5 5 . 0 3 0 . 0 N = 3 0 o.o 5.0 1 0 « 0 1 5 . 0 5 0 » 0 5 5 . 0 —+-3 0 . 0 T E M P E R A T U R E C°C) F i g . 2 3 . E f f e c t ' o f temperature on pulse r a t e i n C_. b l a i s d e l l i s i g n a l s . A = f i r s t pulse group of the male s i g n a l ; B = female s i g n a l . Specimens from B r i t i s h Columbia, Vancouver. . 5 5 Y = - - 0 - 2 0 G 8 + 1-7823X N =• G9 Y = 2 - 9 0 1 8 + 0-4458X N = 3 0 0-0 5 « 0 1 0 - 0 1 5 - 0 EO-0 2 5 « 0 3 0 - 0 T E M P E R A T U R E ( ° C ) F i g . 2 4 . E f f e c t of temperature on pulse r a t e i n C_. wileyae male s i g n a l s . Symbols: t r i a n g l e = pulse r a t e w i t h i n the f i r s t pulse group of the s i g n a l ; X = pulse r a t e w i t h i n subsequent pulse groups of the s i g n a l . Specimens from C a l i f o r n i a , Lassen Co., Said Lake. 56 3 5 . 0 + Y = -7-3334-+ 1-22G9X N = 4 1 3 0 - 0 1 U 2 5 - 0 UJ \ 2 0 - 0 U J 1 5 - 0 U l _J 5 1 0 . 0 5-0 0-0 0.0 5-0 1 0 . 0 1 5 - 0 2 0 - 0 2 5 - 0 T E M P E R A T U R E ( ° C ) 3 0 - 0 F i g . 25. E f f e c t of temperature on pulse r a t e i n C_. wileyae female s i g n a l s . Specimens from C a l i f o r n i a , Lassen Co., Said Lake. 5 7 4 5 "»0 4 0 - 0 . . 3 5 . 0 . . U LU W 3 0 . 0 \ LD E 5 » 0 . . UJ J S O . 0 1 1 5 . 0 1 1 0 . 0 . . 5.0 0.0 Y Y 1 ° 2 7 5 G + 2 ° 2 1 2 3 + 0 9 8 2 2 X 0 - 3 7 4 G X N = G l N = 4 6 x x 0 » 0 5.0 1 0 - 0 1 5 - 0 2 0 - 0 2 5 - 0 T E M P E R A T U R E ( ° D 3 0 . 0 F i g . 2 6 . E f f e c t of temperature on pulse r a t e i n £. expl e t a s i g n a l s . Symbols as i n F i g . 2 4 , but open c i r c l e = pulse r a t e w i t h i n pulse groups of female s i g n a l s . Specimens from B r i t i s h Columbia, Kamloops, Lac du Bois area, LB2. Regression l i n e s are c a l c u l a t e d f o r male s i g n a l s only. 5 8 F i g . 27. E f f e c t of temperature on r e p e t i t o n r a t e of " u n i -pu l s a t e pulse groups" of the second part of the s i g n a l i n C_. b l a i s d e l l i male. Same specimens as i n F i g . 23'A.-5 9 Y = - 0 - 1 7 0 4 + 0 - 1 3 1 0 X N = 92 5 . 0 I 4-01 3«0l u UJ in \ LD CL ZD • CL CD UJ ID LL 1-01 0-0 0.0 5.0 1 0 . 0 1 5 « 0 2 0 - 0 5 5 . 0 3 0 . 0 T E M P E R A T U R E ( ° C ) F i g . 2 8 . E f f e c t of temperature on r e p e t i t i o n r a t e of pulse groups of the second part of the s i g n a l i n C_. wileyae male, Same specimens as i n F i g . 2 4 . 6 0 Y = - 0 - 3 4 1 7 + 0 - 1 G 2 2 X N 5 9 G . 0 4 . u UJ Ul \ LD Q_ Z J • LD UJ Ul _J ZI LL 5.O.. 4-0.. 3-0.. E.O 1-0 0-0 0-0 5.0 1 0 . 0 1 5 « 0 2 0 - 0 2 5 . 0 T E M P E R A T U R E ( ° C ) 3 0 - 0 F i g . 2 9 . E f f e c t of temperature on r e p e t i t i o n r a t e of pulse groups of the s i g n a l s i n C_. e x p l e t a . Symbols: X = male s i g n a l s ; o = female s i g n a l s . Same specimens as i n F i g . 2 6 . Regression l i n e i s c a l c u l a t e d f o r male s i g n a l s only. 6 1 d) Sounds produced as byproduct of c l e a n i n g movements Two types of very f a i n t sounds were observed to be produced and could be recorded when a specimen was r e s t i n g on the hydrophone. These were: i ) Sounds from simultaneous movements of the hind legs over the c o s t a l margins of the fore wings ( F i g . 3 0 A); i i ) Sounds produced by a l t e r n a t e movements of the hind legs when rubbed against abdominal venter or e x t e r n a l g e n i t a l i a ( F i g . 3 0 B). These two sounds were recorded from every species and both sexes, and a l l were s i m i l a r . The main frequency area i n a l l species was around 3-4 k.c/sec and a l l had approximately the same pulse r a t e , about 5 pulses per second f o r simultaneous and 1 0 pulses per second f o r a l t e r n a t e movements of the legs at 22°C. The sounds were most f r e q u e n t l y produced a f t e r a specimen was t r a n s f e r r e d from one container to another. No annual rhythm was found i n the production of these sounds, and they seem to be byproducts of c l e a n i n g movements. M 5 3 1 l 1 S E C O N D S F i g . 30. Sound spectrograms of sounds prod-uced as a byproduct of c l e a n i n g movements. A = C_. andersoni female, simultaneous move-ments of the hind legs on fo r e wings; B = C_. b i f i d a male, a l t e r n a t e movements of the hind legs on fo r e wings. Recorded at 22.8 °C. 6 3 3. L i f e c y c l e , annual rhythm of s t r i d u l a t i o n , and gonad development Generally Corixidae have been reported to s t r i d u l a t e during the sp r i n g and e a r l y summer, or during the breeding season ( M i t i s , 1 9 3 6 ; S c h a l l e r , 1 9 5 1 ; Leston, 1 9 5 5 ; Leston and P r i n g l e , 1 9 6 3 ; Finke, 1 9 6 8 ) . However, i n one case s t r i d -u l a t i o n has a l s o been reported during the f a l l (Larsen, 1 9 3 8 ) . A d e t a i l e d study on l i f e c y c l e of four species of Cenocorixa was undertaken i n order to i n v e s t i g a t e how the annual rhythm of s t r i d u l a t i o n c o r r e l a t e s w i t h the l i f e c y c l e and sexual m a t u r i t y i n t h i s genus. a) L i f e c y c l e i ) C_. b i f i d a and C_. exple t a i n i n t e r i o r B r i t i s h Columbia. The l i f e c y c l e of ce n o c o r i x i d s was studied from stan-dard sweep samples. F i g . 3 1 A shows the sequence of gener-a t i o n s of C_. b i f i d a i n East Lake, and F i g . 3 2 A the same species i n Long Lake. I t can be seen that there were two generations i n both l o c a l i t i e s and i n Long Lake, where the sampling was continued u n t i l l a t e September, the data show>c, that a d u l t s from the second generation as w e l l as some adult s of the f i r s t generation d i d not reproduce, but survived to overwinter. A s i m i l a r l i f e c y c l e p a t t e r n was observed i n _C. b i f i d a i n a l l lakes except LB2. C_. exple t a a l s o showed the same p a t t e r n i n Barnes Lake and Long L a k e . ( i t only occurred i n these lakes and i n LB2). The l i f e c y c l e of the two species were i n phase from the time of appearance of the f i r s t l a r v a e i n the sp r i n g to the f i n a l molting of l a r v a e i n the f a l l . 64 F i g . 33 A shows the l i f e c y c l e of C_. e x p l e t a i n the water body LB2. In t h i s l a k e the species produced three generations: the f i r s t summer generation was very short; the second one was longer and p a r t of i t overwintered ( l i k e p a r t of the f i r s t generation i n other l a k e s ) ; the t h i r d generation s t a r t e d i n September, but was only p a r t i a l l y s u c c e s s f u l . Owing to the low temperatures i n l a t e f a l l , the l a r v a l development was prolonged and many of the l a r v a e f a i l e d to reach the a d u l t stage before freeze-up: they died during winter. _C. b i f i d a i n LB2 produced a s i n g l e generation simultaneously w i t h the f i r s t one of G_. e x p l e t a , and a few l a r v a e of C_. b i f i d a were detected before the second generation of C_. e x p l e t a was completed, but a d u l t s of C_. b i f i d a were not found l a t e r i n the summer ( u n t i l l a t e September when a few, apparently m i g r a t i n g specimens were caught). Standard sweep samples a l s o showed th a t the species were not e q u a l l y abundant i n the various l a k e s . East Lake ( F i g . 31 B) had a f a i r l y high number of _C. b i f i d a a d u l t s i n the e a r l y s p r i n g , but during the summer the number de-creased. The number of i n s e c t s was very high during the l a r v a l l i f e of the f i r s t generation, but low f o r the second generation: Westwick Lake (_C. b i f i d a ) and Boitano Lake North End (_C. b i f i d a ) had s i m i l a r p a t t e r n s . In Long Lake ( F i g . 32 B) the number of _C. b i f i d a a d u l t s was very h i g h i n the e a r l y s p r i n g and a l s o at the time of emergence of the new generations. C_. expleta a l s o produced two generations i n t h i s l a k e , but the number of specimens caught was very low throughout the summer. In Lake Lye 65 (C_. b i f i d a ) and Barnes Lake (C_. b i f i d a and C_. expleta) the l i f e c y c l e p a t t e r n was s i m i l a r to that of C_. b i f i d a i n Long Lake. In the water body LB2 ( F i g . 33 B) there were low num-bers of C_. e x p l e t a specimens during the e a r l y spring and the f i r s t summer generation, but i n the second and t h i r d generations the p o p u l a t i o n increased markedly. The number of C_. b i f i d a specimens was low both i n the e a r l y summer and l a t e f a l l , and none of t h i s species was observed during J u l y and August. The d i f f e r e n c e s i n the l i f e c y c l e of the species i n the v a r i o u s lakes may r e f l e c t d i f f e r e n c e s i n temperature and p r o d u c t i v i t y of the l a k e s . Temperature data f o r each l a k e as w e l l as the a i r temperatures at Westwick Lake are presented i n F i g s . 34-35- In general, the data show few d i f f e r e n c e s i n the lake temperatures, w i t h only LB2 appear-i n g on average s l i g h t l y warmer, and Long Lake a l i t t l e c o o l e r than the others. No study of the primary p r o d u c t i v i t y was undertaken, but c o n d u c t i v i t y c o r r e l a t e s w i t h p r o d u c t i v i t y (Rawson and Moore, 1 9 4 4 ) , and d i f f e r e n c e s i n t h i s environmen-t a l parameter are obvious ( F i g . 36). F i g . 3 1 . Sequence of generations of C_. b i f i d a i n East Lake according to standard sweep samples i n 1 9 6 9 . " A = per cent of adult specimens and d i f f e r e n t l a r v a l i n s t a r s . Symbols: OW = overwintered a d u l t s ; 1 = f i r s t generation a d u l t s ; 2 = second generation a d u l t s ; I to V = d i f f e r e n t l a r v a l i n s t a r s . B = a c t u a l number of specimens caught. Symbols: continuous l i n e = adult specimens (generations as i n A above); dotted l i n e = l a r v a e . 6 6 b CA F i g . 32. Sequence of generations of C_. b i f i d a i n Long Lake according to standard & sweep samples i n 1969. A = per cent of adult specimens and d i f f e r e n t l a r v a l i n s t a r s . B = a c t u a l number of specimens caught. Symbols as i n F i g . 31. 67 b F i g . 3 3 . Sequence of generations of £. expleta i n LB2 according to standard sweep samples i n 1 9 6 9 . A = per cent of adult specimens and d i f f e r e n t l a r v a l i n s t a r s . B = a c t u a l number of specimens caught. Symbols as i n F i g . 3 1 , but 3 = t h i r d gene-r a t i o n . 68 b O 69 a F i g . 34. D a i l y maximum and minimum temperatures at Westwick Lake and Boitano Lake during the summer o 1969. A---= Westwick Lake, a i r temperature; B = West wick Lake, shallow water (20 cm); C = Boitano Lake shallow water (30 cm); D = Boitano Lake North End, shallow water (15 cm). 7 0 a F i g . 3 5 - D a i l y maximum and minimum temperatures i n f i v e lakes i n the i n t e r i o r B r i t i s h Columbia during the summer of 1 9 6 9 . A = East Lake ( 2 0 cm); B = Lake Lye ( 3 0 cm); C = Barnes Lake ( 2 5 cm); D = Long Lake ( 3 0 cm); E = LB2 ( 3 0 cm). 70 b' i 1 1 1 1 1 — M J J A S O F i g . 3 6 . S p e c i f i c c o n d u c t i v i t y of surface water i n ei g h t water bodies i n the i n t e r i o r B r i t i s h Columbia during the summer of 1 9 6 9 . a = LB2; b = Barnes Lake c - Long Lake; d = Lake Lye; e = Boitano Lake; f = Westwick Lake; g = East Lake; h = Boitano Lake North End. 7 2 i i ) C_. andersoni and C_. b l a i s d e l l i , the species of the P a c i f i c Westcoast. Standard sweep samples showed that there were two generations of C_. andersoni i n the Custer g o l f course pond during the summer of 1 9 7 0 ( F i g . 3 7 A). Overwinterd a d u l t s were caught u n t i l mid A p r i l , although a few survived i n the pond u n t i l mid May. The f i r s t generation a d u l t s appeared i n mid June, and the second generation i n e a r l y August. The f i r s t l a r v a e appeared as e a r l y as the beginning of A p r i l , much e a r l i e r than i n the i n t e r i o r species, but the l a r v a l development i n C_. andersoni l a s t e d c o n s i d e r a b l y longer than i n the i n t e r i o r species. The number of i n s e c t s i n the sweep samples throughout the summer was f a i r l y low ( F i g . 3 7 B); the pond apparently has a low p r o d u c t i v i t y ( c o n d u c t i v i t y of the surface water from 2 6 0 micromhos/cm at 25°C i n A p r i l to 4 8 5 micromhos/cm at 25°C i n October). However, water from the pond was a l s o used f o r i r r i g a t i o n of the adjacent g o l f course lawn from June to August, and the sudden decrease i n the water l e v e l may have a f f e c t e d the p o p u l a t i o n of C_. andersoni by de-s t r o y i n g eggs and young l a r v a e which t y p i c a l l y are found at the very edge of the water body. Temperature i n c o a s t a l areas i s much more even through-out the year when compared to the i n t e r i o r temperatures. On the coast there was p r a c t i c a l l y no freeze-up during the winter of 1 9 6 9 - 1 9 7 0 . However, the summer temperatures are almost the same as i n the i n t e r i o r except f o r some hot periods which l a s t longer i n the i n t e r i o r . The e a r l y and 7 3 m i l d spring as w e l l as the r e l a t i v e l y warm l a t e f a l l a pparently a l l o w much longer breeding and growing periods i n the c o a s t a l areas. Thus, although the g o l f course pond was low i n p r o d u c t i v i t y , the long summer allowed the com-p l e t i o n of the two generations. For comparison w i t h the i n t e r i o r temperature data, F i g . 3 8 shows a i r temperature-data from Surrey, Surrey M u n i c i p a l H a l l Weather S t a t i o n , B r i t i s h Columbia (about 2 5 kilometres north of Custer), during the time when observations on C_. andersoni were made. L i f e c y c l e of C_. b l a i s d e l l i was i n i t i a l l y s tudied i n a semitemporary pond i n the corner of 1 6 t h Avenue and Wes-brook Crescent, Vancouver. From October 1 9 6 9 u n t i l May 1 9 7 0 the species was abundant i n the pond. The f i r s t l a r v a e were observed on the same day as those of C_. andersoni i n Custer ( l a t e A p r i l ) , and the i n i t i a l a d u l t s of the f i r s t generation of _C. b l a i s d e l l i appeared i n e a r l y June. However, owing to the temporary nature of the h a b i t a t , these a d u l t s l e f t the pond i n about two weeks as i t was drying up. In J u l y and August the species was o c c a s i o n a l l y found i n other temporary ponds, and i n a permanent pond at the MacCleery Golf Course, Vancouver. However, the p o p u l a t i o n of t h i s l a s t pond was too s c a t t e r e d to give any i n f o r m a t i o n on the sequence of generations, but i t i s assumed th a t only two generations of C. b l a i s d e l l i were produced during the summer. M A M J J A S O F i g . 3 7 - Sequence of generations of C_. andersoni i n Custer g o l f course pond according to standard sweep samples i n 1 9 7 0 . A = per cent of a d u l t specimens and d i f f e r e n t l a r v a l i n s t a r s . B = a c t u a l number of specimens caught. Further explanations as i n F i g . 3 1 . F i g . 3 8 . D a i l y maximum and minimum temperatures at Surrey M u n i c i p a l H a l l Weather S t a t i o n , B r i t i s h Columbia, during the period of November 1 9 6 9 - October 1 9 7 0 . b) Gonad development Females: In the o varian development the f o l l o w i n g three stages were d i s t i n g u i s h e d : A) Undeveloped stage, w i t h no recognis-able oocytes (newly emerged females); B) Intermediate stage, w i t h oocytes r e c o g n i s a b l e , but no chorionated eggs present (overwintering females); and C) Mature stage, w i t h chorion-ated eggs present. F i g . 39 shows l i g h t microscope photo-graphs of these stages i n C_. b i f i d a . Because stages A) and B) grade i n t o each other, and represent immature ovarian stages, they were grouped together i n the f i n a l a n a l y s i s . Males: In spermatogenesis the f o l l o w i n g stages were recognised A) Zone of spermatogonia at the t i p of the t e s t i c u l a r f o l l i c l e s ; B) Zone of r e d u c t i o n d i v i s i o n , w i t h chromosomes c l e a r l y v i s i b l e ; C) Cysts of spermatids i n t h e i r e a r l y developmental stage, while spermatids were s t i l l round; D) Cysts of spermatids i n t h e i r l a t e developmental stage, while spermatids had an oval shape w i t h both ends a c u t e l y produced; E) Cysts of mature spermatozoa, while the sperm had f u l l y developed t a i l s . F i g . 40 shows l i g h t microscope photographs of the stages of spermatogenesis i n C_. b i f i d a . F i g s . 41-43 show the presence of mature and immature specimens i n East Lake (C_. b i f i d a ) , Long Lake (_C. b i f i d a ) , LB2 (C_. e x p l e t a ) , and Custer g o l f course pond (C_. andersoni) The development i n the i n t e r i o r area was somewhat d i f f e r e n t from that i n the c o a s t a l area, and so the two areas are considered s e p a r a t e l y below. 7 7 a F i g - 39« L i g h t microscope photographs of stages of ovarian development i n C_. b i f i d a . A = newly emerged specimen, ovarian f o l l i c l e s undeveloped; B = l a t e f a l l specimen, intermediate stage wi t h oocytes, but no chorionated eggs present; C = mature stage, chorionated eggs present ( t h i s specimen a l s o demon-s t r a t e s the stage when the female i s r e c e p t i v e : eggs i n l a t e r a l o v i d u c t s ) . Length of the sca l e i n d i c a t o r i s one m i l l i m e t e r d i v i d e d i n t o 0.01 mm p a r t s . 7 8 a F i g . 40. L i g h t microscope photographs of stages of spermatogenesis i n C, b i f i d a . A = zone of spermato-gonia at the t i p of the t e s t i c u l a r f o l l i c l e ; B = a cyst i n c l u d i n g r e d u c t i o n d i v i s i o n ; C = cy s t of spermatids i n t h e i r e a r l y developmental stage; D = cys t of spermatids i n t h e i r l a t e developmental stage; E = mature sperm. Length of the s c a l e i n d i c a t o r i s 0.1 mm d i v i d e d i n t o 0.01 mm p a r t s . 78 b A 4 ^^^^^^ d E I —1 Females of the i n t e r i o r species: Samples taken i n the spr i n g 1 9 6 6 by Dr. G. G. E. Scudder from Long Lake showed that on 1 0 A p r i l a few females of C_. b i f i d a had one or two chorionated eggs while none of C_. ex p l e t a females was observed to have eggs; on 1 8 A p r i l most _C. b i f i d a females had 1 0 - 2 0 eggs, but C_. e x p l e t a females were s t i l l without eggs; 1 May both species had chorionated eggs present i n the o v a r i e s . In the spr i n g of 1 9 6 9 both species were f u l l y r e p r o d u c t i v e , w i t h chorionated eggs when f i e l d work commen-ced i n e a r l y May. Overwintered females were found to have eggs present u n t i l the end of the generation: p a r a s i t i s e d specimens lacked chorionated eggs i n the s p r i n g . In LB2 a l l f i r s t generation specimens of both species produced eggs w i t h i n about a week of emergence, but i n a l l other lakes only the i n i t i a l p a r t of the f i r s t generation of each species had f u l l y developed o v a r i e s ; l a t e emerging f i r s t generation females remained s e x u a l l y immature. The second generation of _C. e x p l e t a i n LB2 was observed to be s i m i l a r to the f i r s t one i n other l a k e s , w i t h the i n i t i a l p a r t producing eggs and the l a t e r females remaining s e x u a l l y immature. A l l females of the t h i r d generation of C_. expleta. i n LB2 as w e l l as the second generation of both C_. b i f i d a and £. e x p l e t a i n other lakes remained immature u n t i l the f o l l o w i n g s p r i n g . In previous s t u d i e s i t has been suggested that the i n i t i a t i o n of ovarian a r r e s t i n Corixidae depends on photo-p e r i o d i c e f f e c t s (Young, 1 9 6 5 ; Pajunen, 1 9 7 0 ) • An experiment set up i n l a t e f a l l of 1 9 7 0 f a i l e d to confirm t h i s . Specimens 8 0 of C. b i f i d a were brought to the l a b o r a t o r y from Lake Lye on 8 October and placed i n a c o n t r o l l e d environment cabinet at 5°C and 6 hours photoperiod. 22 days l a t e r , c u l t u r e s w i t h sex r a t i o of 1 male : 2/females were set up at room tem-perature (21-23°C) with 8 hours and 1 6 hours photoperiod. Development of gonads was studied from samples of 1 5 females taken at i n t e r v a l s of four days. The f i r s t female w i t h chor-ionated eggs i n the ovaries was found on the 1 2 t h day at 1 6 hours photoperiod. On the 1 6 t h day two more females at the 1 6 -hours photoperiod possessed chorionated eggs i n the o v a r i e s , but a l s o i n the 8 hours photoperiod, two females w i t h chorionated eggs were found. The experiment i n d i c a t e s that under these c o n d i t i o n s most of the females d i d not a t t a i n sexual m a t u r i t y w i t h i n the 1 6 day t e s t p e r i o d ; d i f f e r e n c e s between the 8 hours and 1 6 hours photoperiod were not detected. Males of the i n t e r i o r species: Overwintered males, p a r a s i t i s e d or u n p a r a s i t i s e d , showed mature sperm present i n samples taken at the time of i c e break-up i n 1 9 6 6 , and throughout the sp r i n g 1 9 6 9 . Males belonging to the i n i t i a l p a r t of the f i r s t summer generation i n a l l Cariboo and C h i l c o t i n lakes had sperm i n the t e s t e s immediately on emergence, and sperm was shown to be present i n the f i f t h l a r v a l i n s t a r that gave r i s e to these a d u l t s . L a t e r , towards the end of the f i r s t generation, newly emerged males of both-er b i f i d a and _C. e x p l e t a were s e x u a l l y immature, as were a l l specimens of the second generation. However, i n l a t e f a l l samples some of the o l d e r specimens were observed to F i g . 4 l . Presence of s e x u a l l y mature specimens of C_. b i f i d a i n East Lake (A) and Long Lake (B) i n 1969. Symbols: v e r t i c a l hatching = s e x u a l l y mature males; s t i p p l e d = s e x u a l l y mature females. OW = overwintered specimens; 1 = f i r s t generation; 2 = • second generation. % P i g . 4 2 . Presence-of s e x u a l l y mature specimens of C. e x p l e t a i n LB2 i n 1 9 6 9 . Symbols as i n F i g . 41, but 3 = t h i r d generation. 00 ro 8 3 have sperm i n the t e s t e s . I t seems probable that these l a t e f a l l i n s e c t s w i t h sperm were f i r s t g eneration specimens from the l a t t e r p a r t of th a t generation. In the Kamloops area, i n the water body LB2, a l l f i r s t g eneration males had sperm at the time of emergence. The second generation was s i m i l a r to the f i r s t one i n other lakes studied, w i t h the i n i t i a l p a r t having sperm on emergence, but the l a t e r p a r t remaining immature. The t h i r d generation remained immature, but l a t e f a l l samples again showed some o l d specimens wi t h mature sperm i n the t e s t e s . Gonad development i n c o a s t a l species: Study of the gonads i n _C. andersoni females showed that no chorionated eggs were found i n overwintering specimens i n l a t e f a l l (November) or e a r l y s p r i n g (March). The f i r s t specimens w i t h chorionated eggs appeared i n e a r l y A p r i l , and eggs were found u n t i l the end of the overwintered generation. Females of the f i r s t summer generation had eggs w i t h i n a week from emergence, and a l l females (except newly emerged) caught from June to mid August had chorionated eggs. The second generation a d u l t s emerging from the beginning of August u n t i l l a t e October, d i d not possess chorionated eggs. These females overwintered, the ovaries developing the f o l l o w i n g s p r i n g . About one t h i r d of males of _C. andersoni caught on 2 1 November 1 9 6 9 had mature sperm i n the t e s t e s , and i n March 1 9 7 0 a l l the males examined had sperm. Males w i t h sperm were found u n t i l the overwintered p o p u l a t i o n died o f f . F i g . 4 3 . Presence of s e x u a l l y mature specimens of C_. andersoni i n Custer g o l f course pond during the summer of 1 9 7 0 . Symbols as i n F i g . 4 l . 8 5 At the beginning of the f i r s t summer generation about h a l f of the males had mature sperm on emergence. Later, however, a l l the f i r s t generation males were found to have mature sperm. The second generation males were without sperm on emergence, but samples taken i n mid October showed mature sperm i n about 2 0 per cent of the specimens, and a l s o the r e s t of them showed cysts of spermatids i n t h e i r l a t e developmental stage. Scattered observations on the gonad development of C_. b l a i s d e l l i i n d i c a t e that overwintered females had chorionated eggs from l a t e March u n t i l the end of the generation. The females of the f i r s t generation i n the temporary pond stud i e d d i d not have chorionated eggs i n the ovaries by the time, they l e f t the pond, which seemed to happen w i t h i n one week from emergence. However, i n the l a b o r a t o r y they were observed to develop chorionated eggs i n about a week. In the permanent pond of the MacCleery Golf Course, on the other hand, females w i t h chorionated eggs were found u n t i l l a t e J u l y . Overwintering males of C_. b l a i s d e l l i from a l l h a b i t a t s had mature sperm i n the t e s t e s when observations were s t a r t e d on 1 5 October 1 9 6 9 , and sperm was present a l l through the winter and i n e a r l y s p r i n g u n t i l the i n s e c t s died. The f i r s t g eneration males had sperm present on emergence. The l a s t summer specimens w i t h mature sperm were caught on 1 9 J u l y 1 9 7 0 , and i n specimens caught on 9 August no mature sperm could be detected. However, on 4 October 1970> a f t e r a very warm p e r i o d , the temporary pond at 1 6 t h Avenue and 8 6 Wesbrook Crescent was found to be repopulated, and two t h i r d s of the male specimens had mature sperm i n the t e s t e s . The main stages of the gonad c y c l e were very s i m i l a r i n a l l four species studied i n d e t a i l . In gener a l , over-wintered females d i d not possess chorionated eggs u n t i l a f t e r i c e break-up or general increase i n temperature i n cases where no true winter freeze-up e x i s t e d . F i r s t gene-r a t i o n females developed chorionated eggs w i t h i n about one week of emergence, but i n the i n t e r i o r species the l a t e r p a r t of t h i s generation remained immature u n t i l the f o l l o w i n g s p r i n g . A l l of the second generation remained immature un-t i l - the f o l l o w i n g s p r i n g . LB2, w i t h a p a r t i a l t h i r d gene-r a t i o n , was an exception from the normal p a t t e r n . In males the overwintered generation had mature sperm before i c e break-up. Males of the f i r s t generation had mature sperm by the l a s t l a r v a l i n s t a r , but i n the i n t e r i o r species the l a t e r p a r t of t h i s generation remained immature u n t i l l a t e f a l l . In the i n t e r i o r species the second generation males remained immature during the f a l l , but matured during winter; i n the c o a s t a l species the second generation males matured during l a t e f a l l . In a l l species the males remaining as im-mature showed an a r r e s t of spermatogenesis i n the stage of cys t s of spermatids i n t h e i r e a r l y developmental stage ( F i g . 4 4 ) . In l a t e f a l l , when development was renewed, o l d males developed mature sperm ( F i g . 4 5 ) , and a l s o the newly emerged males had spermatogenesis i n the stage of cysts of spermatids i n t h e i r l a t e developmental stage, 8 7 F i g . 44. L i g h t microscope photograph of a f o l l i c l e from an ar r e s t e d t e s t i s of C. b i f i d a . Scale i n d i c a t o r 1 mm, d i v i d e d i n t o 0.01 mm p a r t s . 8 8 1 F i g . 4-5. L i g h t microscope photograph of a f o l l i c l e from a mature t e s t i s of C. b i f i d a . Scale as i n F i g . 44. 8 9 c) Annual rhythm of s t r i d u l a t i o n i ) I n t e r i o r species. Male and female s i g n a l s of C_. b i f i d a are Impossible to separate i n f i e l d r ecordings, but those of C_. e x p l e t a can be d i s t i n g u i s h e d e a s i l y . In _C. e x p l e t a only male s i g n a l s were observed i n the f i e l d . Thus, i t i s assumed that i n both species females s t r i d u l a t e so seldom that a l l s i g n a l s recorded i n the f i e l d were produced by males. The distance at which the equipment used picked up s t r i d u l a t o r y s i g n a l s was measured i n Barnes Lake f o r _C. b i f i d a to be about 35 cm and f o r C_. e x p l e t a about 60 cm from the hydrophone. Barnes Lake has a f a i r l y hard bottom covered by only a few centimetres of s o f t d e t r i t u s . I t seems l i k e l y that sounds were picked up i n hard bottom lakes (Long Lake, LB2) from longer distances than i n Barnes Lake, and i n s o f t bottom lakes (Westwick Lake, Boitano Lake, Boitano Lake Worth End, East Lake, and Lake Lye) from shorter distances than i n Barnes Lake. At low p o p u l a t i o n d e n s i t i e s f i e l d r e cording i s not always s u c c e s s f u l (as was the case i n studies on the c o a s t a l s p e c i e s ) . F i e l d recordings made i n l a t e A p r i l 1 9 7 0 and e a r l y May 1 9 6 9 showed that both i n t e r i o r species were s t r i d u l a t i n g at t h i s time.. S t r i d u l a t i o n of _C. b i f i d a continued i n a l l lakes (excluding LB2) u n t i l the end of June. In LB2 the s i g n a l s of C_. b i f i d a were not observed a f t e r e a r l y May, which might be owing to the f a c t that C_. e x p l e t a was s t r i d -u l a t i n g i n t h i s l a k e so a c t i v e l y that i t obscured a l l other s i g n a l s . In J u l y , C. b i f i d a s i g n a l s were no more observed 90 i n Boitano Lake North End, and towards the end of J u l y s t r i d -u l a t i o n a l s o ceased i n East Lake, Westwick Lake, and Long Lake, but continued u n t i l the end of the f i r s t week of August i n Lake Lye, Barnes Lake, and Boitano Lake ( F i g . 4 6 ) . C_. e x p l e t a occurred only i n Barnes Lake, Long Lake, and LB2. S t r i d u l a t i o n of t h i s species was observed i n Long Lake and i n Barnes Lake u n t i l the end of J u l y , but i n LB2 s i g n a l s were recorded as l a t e as 21 August 1969.(Fig. 4 6 ) . In September no s i g n a l s were observed i n any l a k e , and specimens brought i n t o the l a b o r a t o r y d i d not s t r i d u l a t e . On 10 October 1969 some specimens of C_. b i f i d a from Lake Lye and Long Lake were brought i n t o the l a b o r a t o r y , and some of the males began to s t r i d u l a t e immediately at room temperature. S i m i l a r s t r i d u l a t i o n was observed i n specimens of C_. b i f i d a brought i n t o the l a b o r a t o r y on 1 November from ponds cl o s e to Vernon, B r i t i s h Columbia. I t i s probable th a t s t r i d u l a t i o n would a l s o occur i n the f i e l d i f tempe-ratures allow. Specimens of _C. e x p l e t a brought i n t o the l a b o r a t o r y on 1 November 1969 from LB2 and a roadside pond near F a l k l a n d , B r i t i s h Columbia, began to s t r i d u l a t e a f t e r seven days at room temperature. i i ) Coastal species. Study of the s t r i d u l a t i o n of the c o a s t a l species began i n the f a l l of 1969, and the occurrence of s t r i d u l a t i o n was t e s t e d both i n the f i e l d and i n the l a b o r a t o r y . Only male s i g n a l s were observed during recordings. Specimens of both C. andersoni and £. b l a i s d e l l i began to s t r i d u l a t e immediately when brought to the l a b o r a t o r y i n 9 1 mid October 1 9 6 9 , and C_. b l a i s d e l l i was a l s o observed to s t r i d u l a t e i n the f i e l d at temperatures of 7-12°C. Recordings were made throughout the year and s t r i d u l a t i o n was observed i n both species u n t i l the. end of J u l y . F urther, C_. b l a i s d e l l i s i g n a l s were again detected i n the beginning of October, and _C. andersoni s i g n a l s i n mid October 1 9 7 0 ( F i g . 4 6 ) . F i g . 46 shows that g e n e r a l l y the annual rhythm of s t r i d -u l a t i o n i n Cenocorixa males i n B r i t i s h Columbia i s about the same i n a l l species, i . e . they s t r i d u l a t e when they are s e x u a l l y mature. However, although males.begin to s t r i d u l a t e i n l a t e f a l l females do not respond to them u n t i l the f o l -lowing s p r i n g which i s the time of maturation of the females. The main d i f f e r e n c e between the i n t e r i o r and c o a s t a l species i s that the r e l a t i v e l y high temperatures on the coast enable the species to s t r i d u l a t e much of the win t e r , while i n the i n t e r i o r , the low temperature of the water i n h i b i t s s t r i d -u l a t i o n at t h i s time. F i g . 46. Observed annual rhythm of s t r i d u l a t i o n and sexual m a t u r i t y i n four species of Cenocorixa. £. b i f i d a : a = Boitano Lake North End; b = East Lake; c = Westwick Lake; d = Long Lake; e = Barnes Lake; f = Lake Lye; g = Boitano Lake. C_. e x p l e t a : h = Long Lake; i = Barnes Lake; j = LB2. C_. andersoni: k - Custer, g o l f course pond. _C. b l a i s d e l l i : 1 = Vancouver, 16th Avenue and Wesbrook Crescent pond and MacCleery Golf Course pond. Symbols: continuous l i n e = s t r i d u l a t i o n observed; arrows = s e x u a l l y mature specimens present i n samples between the time i n d i c a t e d by the arrows: males above, females below the l i n e ; * - beginning of observations; t = end of observations. 0 *T r [1 1 t l i tit t l i t l i t l i t l i t l i t l i t l i t l i * * * * * * * ti 9 3 d) Miscellaneous observations on other species and l o c a l i t i e s During the course of the f i e l d work:, s e v e r a l l o c a l i t i e s were v i s i t e d o c c a s i o n a l l y i n order to o b t a i n other species of the genus. At the same time a d d i t i o n a l comparative data were obtained on l i f e c y c l e s . Information was as f o l l o w s : C. b i f i d a : This species was found s t r i d u l a t i n g and mating i n southern A l b e r t a on 2 1 - 2 2 May 1 9 7 0 , but no la r v a e were detected. On 6 August most of the males were n o n - s t r i d -u l a t i n g , but a few s t r i d u l a t i n g ones were a l s o observed and many l a r v a e were c o l l e c t e d at the same l o c a l i t y . On 8 J u l y the species was found i n northern Utah at 2400 m a l t i t u d e ; c o p u l a t i n g p a i r s and s t r i d u l a t i o n were observed, and a few IV and V i n s t a r l a r v a e were caught a l s o . I t seems probable t h a t the l i f e c y c l e both i n southern A l b e r t a and northern Utah i s s i m i l a r to that i n i n t e r i o r B r i t i s h Columbia, with two generations per year. C_. k u i t e r t i : The species was found s t r i d u l a t i n g and mating at 3 0 0 0 m a l t i t u d e i n C e n t r a l C a l i f o r n i a (Tioga Pass) on 5-6 J u l y 1 9 7 0 . No la r v a e were detected. I t seems obvious that the species has only one generation per summer owing to the low temperatures at high a l t i t u d e s . C_. utahensis: The species was found i n southern A l b e r t a ( s y m p a t r i c a l l y w i t h C_. b i f i d a and C_. dakotensis) s t r i d u l a t i n g and mating on 2 1 - 2 2 May 1 9 7 0 . On 6 August no C_. utahensis specimens were detected at t h i s l o c a l i t y . Scattered populations of the species were found i n southern and northern Utah on 7-8 J u l y 1 9 7 0 : a d u l t males were s t r i d u l a t i n g , females had chorionated eggs i n o v a r i e s , and a l s o l a r v a e were c o l l e c t e d . 9 4 In southern Washington both on 1 0 J u l y and 1 August 1 9 7 0 , one s t r i d u l a t i n g male specimen was caught. I t seems pro-bable that the species has at l e a s t two, maybe three gene-r a t i o n s per year i n Utah, but i t i s not known whether the species breeds s u c c e s s f u l l y i n A l b e r t a or Washington. C_. dakotensis: The species was found i n southern A l b e r t a on 2 1 - 2 2 May 1 9 7 0 , s y m p a t r i c a l l y w i t h C_. b i f i d a and _C. utahensis. Adult males s t r i d u l a t e d when brought i n t o the l a b o r a t o r y and females had chorionated eggs i n the ova-r i e s . No l a r v a e were detected i n the f i e l d . On 6 August the species was not found i n the same l o c a l i t i e s . C_. b l a i s d e l l i : On 1 8 - 2 0 January 1 9 7 0 , the species was found overwintering i n C a l i f o r n i a (San F r a n c i s c o area and Clam Beach); only adult specimens were observed. Males were s t r i d u l a t i n g , and females d i d not have chorionated eggs i n the o v a r i e s . The number of generations at these l o c a l i t i e s Is not known. C_. wileyae: In lower a l t i t u d e s (up to 2 0 0 0 m) the species was found i n e a r l y J u l y i n C a l i f o r n i a , Oregon, Nevada, and Utah as s t r i d u l a t i n g a d u l t s and various l a r v a l i n s t a r s . On 1 August some s t r i d u l a t i n g a d u l t s were caught i n southern Washington. However, i n e a r l y J u l y at high a l t i t u d e s (2400 to 3 0 0 0 m) i n C a l i f o r n i a , only a d u l t s were detected. I t seems p o s s i b l e that the species has two to three generations per year at low a l t i t u d e s , but only one at high a l t i t u d e s . _C. e x p l e t a : On 29 August 1 9 6 9 the species was found s t i l l s t r i d u l a t i n g i n c e n t r a l Washington (Soap Lake), and a l s o various l a r v a l i n s t a r s were caught. A s i m i l a r s i t u a t i o n was observed on 6 August 1970 at the same l o c a l i t y . I t seems l i k e l y t hat the species has three generations per year i n t h i s l o c a l i t y , and the t h i r d generation i s probably more complete than i n LB2 i n B r i t i s h Columbia. 96 4. D i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y . In many studies on European Corixidae i t has been observed that the bugs have a d i e l p e r i o d i c i t y i n t h e i r s t r i d u l a t i n g a c t i v i t y ( c f . Jansson, 1968). In order to i n v e s t i g a t e the v a l i d i t y of the f i e l d recordings which were made u s u a l l y during daytime i n the present study, i t was necessary to know the d i e l p e r i o d i c i t y of the s t r i d -u l a t i n g a c t i v i t y of the various species. With C_. b i f i d a t h i s was studied' in' Westwick Lake and Barnes Lake, and wit h _C. e x p l e t a i n LB2 during the summer of 1969 by r e -cording f i v e minutes every hour over a 24 hour p e r i o d i n s i t u . The r e s u l t s ( F i g . 47) i n d i c a t e that a d i f f e r e n c e e x i s t s between the two species, although the number of s i g n a l s obtained f o r C_. b i f i d a was not very l a r g e , and i n _C. e x p l e t a i t was impossible to count i n d i v i d u a l s i g n a l s i f more than 100 s i g n a l s were recorded during the f i v e minute periods. Nevertheless, although s i g n a l s of both species were recorded at a l l times of day, C_. expleta. seemed to have highest s t r i d u l a t i n g a c t i v i t y at nighttime, while _C. bifida,was most a c t i v e during the afternoon. During the summer of 1970 a l a b o r a t o r y study of the d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y was c a r r i e d out on a l l species. In these experiments 10 male specimens were placed together i n a c u l t u r e t r a y and kept under n a t u r a l l i g h t c o n d i t i o n s at uniform room temperature over a f i v e day pe r i o d . Recordings were made f o r f i v e minutes each hour. The r e s u l t s of these experiments ( F i g s . 48-51) wi t h comparisons to f i e l d recordings were as f o l l o w s : 9 7 _C. b i f i d a ( F i g . 4 8 A): During the i n i t i a l two days of the experiment the species was most a c t i v e during the day, but subsequently the a c t i v i t y was more g e n e r a l l y d i s t r i b u t e d over the 24 hours. For f i e l d recordings see F i g . 4 7 A-E. C_. k u i t e r t i ( F i g . 4 8 B) : In the f i r s t two days c l e a r n i g h t a c t i v i t y was recorded. The t e s t was i n t e r r u p t e d f o r three days ( i n order to c a r r y out the t e s t s w i t h C_. w i l e y a e ) , and when continued on the 6 t h to 8 t h day, the s t r i d u l a t i o n occurred both i n the day and ni g h t . No s i g n a l s were obtained i n f i e l d recordings made during the day. _C. andersoni ( F i g . 4 9 ) : Highest a c t i v i t y was recorded every day of the f i v e day t e s t p e r i o d at dusk. No s i g n a l s were observed i n f i e l d recordings made during the day. £. dakotensis ( F i g . 50 A): C l e a r l y n o c t u r n a l a c t i v i t y was observed on the f i v e days t e s t e d . No s i g n a l s were obtained i n f i e l d recordings made during the day. 9.- b l a i s d e l l i ( F i g . 5 1 ) : Signals were recorded during a l l hours, but the highest a c t i v i t y was at dusk and the lowest around noon. Si g n a l s were a l s o observed i n f i e l d recordings made during the day and at dusk. _C. wileyae ( F i g . 4 8 C): Records show t h i s to be a f a i r l y i n a c t i v e species s t r i d u l a t i n g only from dawn to noon. The t e s t was c a r r i e d out i n two parts (2 + 3 days), because C_. k u i t e r t i was test e d f o r three days i n the mean time. In f i e l d recordings _C. wileyae s i g n a l s were obtained at a l l hours of the day. C_. ex p l e t a ( F i g . 50 B): According to the l a b o r a t o r y experiment t h i s species i s f a i r l y i n a c t i v e , s t r i d u l a t i n g mostly at nighttime. In the f i e l d s i g n a l s were obtained at a l l times of the day ( F i g . 47 F ) . In C_. utahensis observations were s c a t t e r e d because at the most only three males were a v a i l a b l e at any one time. However, t h i s species seemed to have the highest a c t i v i t y at dawn and dusk. No s i g n a l s were obtained i n f i e l d recordings made during the day. In cases when the p e r i o d i c i t y i n the s t r i d u l a t i n g a c t i v i t y changed during the t e s t p e r i o d , i t i s considered that the f i r s t days show a p e r i o d i c i t y s i m i l a r to the n a t u r a l one. Comparison of the f i e l d recordings .arid/;; the experimental recordings i n C_. b i f i d a ( F i g s . 47 A-E and 48 A) support t h i s concept. Jansson (1968) has shown experimentally i n a Euro-pean c o r i x i d , C a l l i c o r i x a producta (Reut.), that the d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y i s i n f l u e n c e d by temperature, although the main f a c t o r seems to be l i g h t . Thus the f i n a l day p e r i o d i c i t y i n the l a b o r a t o r y was probably not always n a t u r a l , owing to the even room temperature. F i g . 4 7 . In s i t u observations on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of C_. b i f i d a and C_. e x p l e t a . C_. b i -f i d a : A = Westwick Lake, 1 2 - 1 3.V. 1 9 6 9 ; B = Westwick Lake, 2 5 - 2 6 . V . 1 9 6 9 ; C = Westwick Lake, 1 6 - 1 7 . V T . 1 9 6 9 ; D = Barnes Lake, 2 7 - 2 8 . V . 1 9 6 9 ; E = Barnes Lake, 7 - 8 . V I . i 9 6 9 . C. e x p l e t a : F = LB2, 2 1 - 2 2 . V . 1 9 6 9 . Ordinate (lower): t o t a l number of s i g n a l s during f i v e minutes (more than 1 0 0 s i g n a l s per f i v e minutes i s impossible to count i n C_. e x p l e t a ) , (upper): temperature. Hatching = time between sunset and s u n r i s e . 100 F i g . 48. Laboratory experiments on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of C_. b i f i d a (A), _C. k u i t e r t i (B), and C_. wileyae (C). Ordinate: t o t a l number of s i g n a l s prod-uced by 10 male specimens i n a c u l t u r e t r a y during f i v e minutes. Hatching = time between sunset and s u n r i s e ( P a c i f i c d a y l i g h t time). Dates of the experiments: A: 28.IV.-3.V.1970; B: 15-17.VII.1970 and 20-23.VII.1970; C: 17-19.VII.1970 and 2 3 - 2 6 . v i i . 1 9 7 0 . 1 0 1 1 2 0 1 0 0 1 2 12 1 2 12 12 P i g . 4 9 . Laboratory experiment on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of C. andersoni. Date of the experi-ment 1 5 - 2 0 . V I . 1 9 7 0 . Further explanations as i n F i g . 4 8 . 102 F i g . 50. Laboratory experiments on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of _C. dakotensis (A) and C_. expleta (B). Dates of the experiments: A: 6-11.VI. 1970; B: 29.V.-3".VI. 1970. Further explanations as i n F i g . 48. 1 0 3 i 12 12 12 12 12 F i g . 5 1 . Laboratory experiment ori d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of £. b l a i s d e l l i . A = t o t a l number of the f i r s t pulse groups of the s i g n a l s observed during f i v e minute recordings; B = t o t a l number of u n i p u l s a t e ' c l i c k s ' observed. Date of the experiment 2 1 - 2 6 . V I . 1 9 7 0 . Further explanations as i n F i g . 48 . 104 5 . Behavioral r o l e of s t r i d u l a t i o n a) Male and female response to s t r i d u l a t o r y s i g n a l s and some other s t i m u l i The t e s t s c a r r i e d out on the d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y provided s u i t a b l e m a t e r i a l f o r ana-l y s i n g response of males to s i g n a l s of other males. F i g . 52 represents an example of a four minute recording from each species studied. I t can be seen that i n most species there i s some tendency f o r the s i g n a l s to be grouped. I t would appear thus .that the males respond to s i g n a l s of other c o n s p e c i f i c males by s t r i d u l a t i n g . In i n i t i a l s t u d i e s i n the f i e l d and i n the l a b o r a t o r y i t was f r e q u e n t l y observed that when a r e p r o d u c t i v e l y a c t i v e male came c l o s e to another specimen, the male produced a few s i g n a l s , approached the other specimen, and of t e n t r i e d to copulate. On the other hand, sometimes c o p u l a t i o n attempts were observed to occur without any i n t r o d u c t o r y s i g n a l s . I f the specimen being approached was a female, the l a t t e r o f t e n turned away and moved o f f when the male was s t r i d u l a t i n g , or i f c o p u l a t i o n was attempted by c l a s p i n g the female, the attempt f a i l e d owing to a rel e a s e behavior of the female. However, during the pe r i o d of A p r i l - J u l y , c o p u l a t i n g p a i r s were f r e q u e n t l y observed i n the f i e l d , but i n i t i a t i o n of a s u c c e s s f u l c o p u l a t i o n was not observed. I f the specimen being approached was another male, the l a t t e r answered the s i g n a l s of the f i r s t male and both s t r i d -u l a t e d i n t u r n , u n t i l one of them nudged the other one away. A l t e r n a t i v e l y , the male approached simply came and nudged F i g . 52 . R e p e t i t i o n r a t e of s i g n a l s produced by 10 male specimens i n a sample four minute t e s t p e r i o d , a = _C. b i f i d a ; b = C.. k u i t e r t i ; c = C_. andersoni; d = C_. dakotensis; e = C. b l a i s d e l l i ; f = _C. wileyae; g = C_. e x p l e t a . Symbols: each bar represents one s i g n a l . Length of bar gives i n d i c a t i o n of s i g n a l l e n g t h In C_. b l a i s d e l l i each t h i n l i n e represents a u n i p u l s a t e ' c l i c k ' and a bar repre sents a m u l t i p u l s a t e f i r s t p a r t of a s i g n a l . E E e E E E E e E E E E e8 L 105 b m E E B CO CD •rt 106 the s t r i d u l a t i n g one away without s t r i d u l a t o r y response. In these i n t e r a c t i o n s the i n s e c t that was nudged would u s u a l l y swim away, and the i n s e c t that nudged oft e n showed a. chasing r e a c t i o n and sometimes followed the other specimen f o r s e v e r a l seconds. In these cases i t o f t e n nudged the persued specimen again i f t h i s d i d not swim very f a r . The r o l e of s t r i d u l a t i o n between males was studied i n more d e t a i l i n the l a b o r a t o r y w i t h C_. b i f i d a and C_. b l a i s -d e l l i by p l a c i n g a. few specimens i n t o the sand l i n e d bath-tub and observing t h e i r behavior. In C_. b i f i d a i t was observed that when two males happened to come clo s e to each other, the sequence of events recorded i n the f i e l d observations was repeated. However, i t was a l s o observed th a t an a u d i t o r y stimulus alone could i n i t i a t e the approach behavior; i n t h i s case the approach swimming was a c i r c l i n g movement ending w i t h i n c l o s e range of the s t r i d u l a t i n g specimen, and then the s i t u a t i o n was continued as described i n the case of v i s u a l stimulus. On the other hand, i n _C. b l a i s d e l l i a u d i t o r y s t i m u l i were observed to induce the males to s t r i d u l a t e , but i t was not observed to i n i t i a t e any moving a c t i v i t i e s ; only v i s u a l s t i m u l i together w i t h a u d i t o r y s t i m u l i i n i t i a t e d the behavior that would lead to nudging away the other specimen. Thus i t seems l i k e l y t h a t the nudging and chasing behavior between males i s a kind of a g o n i s t i c behavior s e r v i n g to space out i n d i v i d u a l s : s t r i d u l a t i o n apparently i s o f t e n a stimulus important i n t h i s context. However, i t seemed p o s s i b l e that s t r i d u l a t i o n a l s o could f u n c t i o n 107 i n sex r e c o g n i t i o n , but there was l i t t l e to i n d i c a t e t h a t i t would serve as a premating stimulus. In order to c l a r i f y f u r t h e r d e t a i l s i n the male and female response to male s i g n a l s c e r t a i n l a b o r a t o r y e x p e r i -ments were arranged. These were designed to f o l l o w the l i n e of i n v e s t i g a t i o n s adopted by S c h a l l e r (1951) and Finke (1968) whereby a l l a c t i v i t i e s of experimental animals were observed and q u a n t i f i e d . The species used f o r these t e s t s was _C. b i f i d a . The experimental animals used were as f o l l o w s : a) One male kept alone during the e n t i r e t e s t period (11 days). b) One male picked at random from a p o p u l a t i o n of 20 cfd and 20 ??. c') Two. females picked at random from a p o p u l a t i o n of 30 $?. d) Two females picked at random from a p o p u l a t i o n of 20 dc? and 20 ?$ . The d i f f e r e n t t e s t c o n d i t i o n s were as f o l l o w s : i ) Alone (one male or two females at a time). i i ) With s t r i d u l a t o r y s t i m u l i (4-5 s t r i d u l a t i n g males i s o -l a t e d i n a cage placed i n t o the t e s t c o n t a i n e r ) . i i i ) With chemical s t i m u l i : i n water p r e v i o u s l y occupied by two females from the 30 female c u l t u r e . i v ) With chemical s t i m u l i : i n water p r e v i o u s l y occupied by two males from the 30 male c u l t u r e . v) With v i s u a l s t i m u l i (another specimen i s o l a t e d i n a t r a n s -parent cont a i n e r , or i n t r o d u c i n g a dead pinned specimen). v i ) Back alone i n the o r i g i n a l t r a y . 108 The experiments on chemical s t i m u l i were c a r r i e d out i n order to t e s t p o s s i b l e presence of a pheromone. A clue f o r t h i s was obtained from an observation on Sigara omani (Hung.) males that showed that these began to s t r i d u l a t e very a c t i v e l y when they were t r a n s f e r r e d to a t r a y where females of t h i s species had been kept p r e v i o u s l y . The combinations used i n the t e s t s were as f o l l o w s : Experimental animals Test c o n d i t i o n s a) i , i i , i i i , ( i v ) , ( v ) , v i , b) i , i i , i i i , - ( v ) , v i , A c t i v i t i e s studied were cl a s s e d under s i x headings: 1) Cleaning, 2) Turning on the spot, 3) Short swimming (swimming bursts t h a t l a s t e d l e s s than f i v e seconds), 4) Long swimming (continuous swimming which l a s t e d more than f i v e seconds), 5) Surface v i s i t s ( f o r renewal of a i r storage)., and 6) S t r i d u l a t i o n . The s t r i d u l a t o r y s i g n a l s produced by both the experimental animals and the specimens used to provide the t e s t s t i m u l i were recorded. Experiments on v i s u a l s t i m u l i u n f o r t u n a t e l y d i d not always work p r o p e r l y because the experimental specimens were f r e q u e n t l y g r e a t l y d i s t u r b e d by the p l a c i n g of the transparent container i n t o the t r a y . However, i n a few s u c c e s s f u l t e s t s i t seemed th a t females d i d not respond to the v i s u a l stimulus of another specimen, but o c c a s i o n a l l y c) d) 11, ( I v ) , ( v ) , ( i v ) , ( v ) , Conditions mentioned i n brackets were not tes t e d r e g u l a r l y . 109 males d i d i n t h a t they were observed to t u r n towards the specimen i n the container, produce a few s i g n a l s , and f i n a l l y t r y to reach the i n s e c t i n s i d e the container. A l s o a pinned dry specimen was introduced to the experimental animals, but unnatural movements during t h i s i n t r o d u c t i o n seemed again to be a d i s t u r b i n g f a c t o r . A t e s t f o r the presence of male odor was c a r r i e d out only three times f o r each type of experimental animals. No d i f f e r e n c e was observed when compared to the s i t u a t i o n when no s t i m u l i were present. Table I I I shows the r e s u l t s of observations on the behavior of the male specimens of C_. b i f i d a under c o n d i t i o n s i , i i , i i i , and v i above: these r e s u l t s show that i n turns on the spot, surface v i s i t s , and c l e a n i n g there was no s i g n i f -i c a n t d i f f e r e n c e between the t e s t c o n d i t i o n s . However, the number of short swims was s i g n i f i c a n t l y greater when s t r i d -u l a t o r y s t i m u l i from other males were present. Long swims, on the other hand, occurred at an equal r a t e i n the case of the male kept alone a l l the time, but i n males kept w i t h females there seems to be a d i f f e r e n c e between the c o n d i t i o n s where the males were alone or w i t h s t r i d u l a t o r y s t i m u l i : the males swam more i n the l a t t e r case. S i g n i f i c a n t d i f f e r e n c e s were a l s o found i n both experimental s e r i e s i n the number of s t r i d u l a t o r y s i g n a l s produced by the experimental animals: the male kept alone a l l the time s t r i d u l a t e d mostly when the female odor was present; however, the males kept w i t h females d i d not react to the female odor, but reacted to s t r i d u l a t o r y s t i m u l i . Table I I I . A c t i v i t i e s of C_. b i f i d a males under various t e s t c o n d i t i o n s . A n a l y s i s by Friedman two-way a n a l y s i s of variance. Test c o n d i t i o n s as authorised on page 107, 15 minute t e s t p eriods, each t e s t repeated s i x times. Explanations: 0*/$ = mixed c u l t u r e ; * - value d i f f e r s s i g n i f i c a n t l y from a l l others; * = s i g n i f i c a n t d i f f -erence only between the two values marked by t h i s s i g n (comparison by Wilcoxon matched-pairs ranked-sign t e s t ) . Specimen S p e c i f i c Average number of s p e c i f i c a c t i v i t y per test e d a c t i v i t y experimental period under t e s t c o n d i t i o n s 1 1 1 1 1 iv 2 P r o b a b i l i t y of o b t a i n i n g the r e s u l t by chance cr alone cleaning 0.17 O.83 • .3.50 1.83 2. 35 P < • 7;0 0* from o*/$ 2.50 0.83 2.17 1.50 1. 35 P < .80 0* alone turns 0.50 0.33 1.00 0.17 1. 15 P < .80 0* from 0*/? 2.50 4.33 0.17 1.50 0. 35 P = • 95 0* alone short swims 2.83 11.33* 2.33 2.00 12. 05 P < .01 0" from o*/$ 6.5O 17.33* 4.00 5.83 22. 50 P < . 001 d* alone long swims 0.00 O.50 0.17 0.00 1. 10 P < .80 0* from o*/$ 1.67* 5.17* 4.83 3.00 9- 77 P < .05 cf alone surfacings 1.17 0.67 2.00 0.83 2. 65 P < .50 cf from cf/$ 1.50 3.50 4.00 2.50 2. 65 P < .50 cf alone s t r i d u l a t i o n 7.00 14.33 32.17* 5.67 11. 35 P < .01 cf from o"/$ O.67 I6.83* 4.00 2.83 12. 75 P < . 01 (—1 H O I l l The r e s u l t s of the t e s t s w i t h females are shown i n Table IV ( t e s t c o n d i t i o n s i and i i ) . No s i g n i f i c a n t d i f f -erences could be detected between the t e s t c o n d i t i o n s i n the amount of c l e a n i n g or the number of turns on the spot. However, the females kept i s o l a t e d from males showed a s i g n i f i c a n t r e d u c t i o n i n the number of short and long swims as w e l l as i n surface v i s i t s when male s i g n a l s were present. A l s o the females kept w i t h males showed a s i g n i f i c a n t red-u c t i o n i n the number of long swims and surface v i s i t s when s t r i d u l a t o r y s t i m u l i were present, but no d i f f e r e n c e was detected i n the number of short swims. In order to check that there were no d i f f e r e n c e s i n the numbers of s t r i d u l a t o r y s i g n a l s produced by i n s e c t s used to provide the t e s t s t i m u l i , the number of s i g n a l s produced during each experiment were compared by a Friedman two-way a n a l y s i s of v a r i a n c e : no s i g n i f i c a n t d i f f e r e n c e was found. A l s o the f a c t that each t e s t was repeated every second day, the e n t i r e t e s t p e r i o d being thus 11 or 13 days, was designed i n order to f i n d out i f the behavior of the bugs would change during the time under va r i o u s c u l t u r e s : no evidence of any change was found. The foregoing experiments demonstrated t h a t : a) Males s t r i d u l a t e d spontaneously. b) There was an increase i n swimming and s t r i d u l a i n g a c t i v i t y i n males when stimulated by s i g n a l s of other males. c) A male which had been separated from other specimens f o r ;. some time s t r i d u l a t e d a c t i v e l y when In presence of female odor, whereas males maintained w i t h females d i d not react 1 1 2 Table IV. A c t i v i t i e s of CJ. b i f i d a females under various t e s t c o n d i t i o n s . A n a l y s i s by Wilcoxon matched-pairs ranked-s i g n t e s t . Test c o n d i t i o n s as authorised on page 1 0 7 , 1 5 minute t e s t p e r i o d s , each t e s t repeated seven times. Explanations: 2 ? ? alone - two females from 3 0 female c u l t u r e ; 2$?/V = two females from 2 0 male and 2 0 female c u l t u r e ; n.s. = no s i g n i f i c a n t d i f f e r e n c e between the t e s t c o n d i t i o n s . Specimens S p e c i f i c Average nu: t e s t e d a c t i v i t y a c t i v i t y p p e r i o d und i 2?? alone c l e a n i n g 2.29 2??/cr 3.^3 2?? alone turns 8.86 2$$/cr 6.86 2$$ alone short swims 20.14 2$?/cT 11.00 2?? alone long swims 6.86 2??/^ 10.57 2?? alone s u r f a c i n g s 8 . 4 3 2??/cr 7.43 ruber of s p e c i f i c P r o b a b i l i t y er experimental of ob t a i n i n g er t e s t c o n d i t i o n the r e s u l t i i by chance 3 . 2 9 n. s. 3.14 n. s. 2.86 n.s. 2.57 n.s. 9.14 p - .01 10.00 n. s. 1.57 P < .05 3 . 4 3 P < .05 4.86 p < . 0 2 5 4.86 p < . 0 2 5 to female odor. d) Females responded to male s i g n a l s by remaining motionless. e) Females d i d not s t r i d u l a t e . Categories a) and b) above could be explained as an a g o n i s t i c behavior spacing out the males. However, c) and d) i n d i c a t e that s t r i d u l a t i o n might a l s o have something to do w i t h premating behavior. One could hypothesize that a spontaneously s t r i d u l a t i n g male, a f t e r having been apart from females, i s induced to c a l l a c t i v e l y by odor of a female i n the v i c i n i t y . The s i g n a l s of the male would keep the female s t a t i o n a r y , thus g i v i n g the male a chance to f i n d the mate according to odor. 114 b) Mating i n C. b i f i d a Further experiments were c a r r i e d out i n order to check whether the hypothesis on existence of s t r i d u l a t i o n - o d o r i n t e r a c t i o n could be shown to have any r o l e i n a c t u a l mating of the bugs. A s i n g l e female _C. b i f i d a from the c u l t u r e of 30 females kept i s o l a t e d from males f o r 20 days, was introduced i n t o the t r a y of the male kept alone f o r the previous experiments. Close observation of both i n s e c t s w i t h continuous tape re c o r d i n g was c a r r i e d out. At f i r s t , both specimens were observed to swim around apparently at random, but a f t e r about three minutes the male produced a s i g n a l , and immediately afterwards the female, remaining s t a t i o n a r y , responded by producing a s t r i d u l a t o r y signal'. S t r a i g h t away the male s t a r t e d to swim r a p i d l y i n small c i r c l e s , stopping at i n t e r -v a l s to s t r i d u l a t e again. The female remained motionless and answered the male s i g n a l each time, but at no time d i d the female swim i n response. The male continued searching, but e v i d e n t l y was not able to o r i e n t a t e d i r e c t l y towards the female (owing to echo i n the p l a s t i c t r a y used f o r the t e s t , see below). F i n a l l y , one and a h a l f minutes a f t e r the f i r s t male s i g n a l was recorded, the male l o c a t e d the female and a s u c c e s s f u l c o p u l a t i o n occurred. This c o p u l a t i o n l a s t e d about 15 minutes. H a l f a minute a f t e r the c o p u l a t i o n was completed the male began to s t r i d u l a t e again, but at t h i s time there was no s t r i d u l a t o r y response from the female. Once mated, the female would not respond to a s t r i d u l a t i n g male f o r s e v e r a l days. This experiment was repeated s e v e r a l times 115 w i t h C_. b i f i d a w i t h the same r e s u l t . Even i f a c o p u l a t i o n was i n t e r r u p t e d 2-3 seconds a f t e r the g e n i t a l contact, t h i s was enough f o r the female not to respond any more to the male s t r i d u l a t i o n by answering. The f a c t that males do o r i e n t a t e according to the female s i g n a l s could not be studied i n the c u l t u r e t r a y s used f o r the f i r s t mating experiments, e v i d e n t l y because of echoes from the w a l l s . However, i n experiments c a r r i e d out i n the sand l i n e d bathtub i t was demonstrated t h a t the female s i g n a l s do serve i n o r i e n t a t i o n of the male: when female s i g n a l s were played back, from tape recordings the males congregated around the loudspeaker and would remain so p o s i t i o n e d as long as the playback was continued, t r y i n g to f i n d "the female" i n the loudspeaker. A l s o when a r e c e p t i v e female was placed i n t o the bathtub w i t h a s t r i d u l a t i n g male, the former d i d not need to answer the male c a l l s more than once when the male swam s t r a i g h t to the female and copulated. Only females kept i s o l a t e d from males f o r at l e a s t a week were found to respond to male s i g n a l s by s t r i d u l a t i n g . Females from mixed c u l t u r e s d i d not s t r i d u l a t e . Such non-s t r i d u l a t i n g females were o f t e n t a r g e t s f o r c o p u l a t i o n attempts, but these attempts were never observed to be s u c c e s s f u l . The females, i f clasped by males i n attempt to copulate, would adopt a r e l e a s e behavior which c o n s i s t s of vigorous swimming, coming up tb-'the water surface, t u r n i n g almost upside down at the surface, and d i s l o d g i n g the male w i t h the hind l e g s . In other cases when a s t r i d u l a t i n g male was clo s e to an unreceptive female, the female swam away 1 1 6 (henceforth c a l l e d "escape" r e a c t i o n ) or towards i t , so t h a t i t d i s t u r b e d the male ( " a g o n i s t i c " r e a c t i o n ) . This a g o n i s t i c behavior i n the females was d i f f e r e n t from the a g o n i s t i c behavior between two males In that the females d i d not chase the male a f t e r they had nudged the male away. F i g . 5 3 shows the sequence of events i n the s u c c e s s f u l mating i n C. b i f i d a . 1 1 7 R e p r o d u c t i v e l y a c t i v e male Receptive female spontaneous s t r i d u l a t i o n ^ remains s t a t i o n a r y ; s t r i d u l a t e s searches; o r i e n t a t e s towards the female s i g n a l ; s t r i d u l a t e s ^remains s t a t i o n a r y ; „stridulates. searches; observes the female ( v i s u a l s t i m u l u s ) ; approaches stays passive on approach of the male mounts; copulates F i g . 5 3 . Diagram on the sequence of events i n a s u c c e s s f u l mating i n C. b i f i d a . 118 c) S p e c i f i c d i f f e r e n c e s i n the mating behavior Experiments on mating were then conducted w i t h a l l other species. These showed the sequence of events to be much the same i n a l l species. Experiments c a r r i e d out i n the bathtub were used to determine the distance at which a responsive female answered the s i g n a l s from a c o n s p e c i f i c male, and a l s o the distance at which a male answered the s i g n a l s of a, female. The r e s u l t s of these experiments, which u t i l i z e d both s t r i d u l a t i n g specimens and playback: from tape recorder through an under-water loudspeaker, are given i n Table V. Some s p e c i f i c d i f f e r e n c e s between the species during t h e i r mating behavior were found and are summarised i n Table VI f o r males and i n Table V I I f o r females. The stimulus r e l e a s i n g the mating behavior i n males seems to be u s u a l l y both a u d i t o r y and v i s u a l , but i n _C. dakotensis and C_. wileyae i t seems to be a u d i t o r y only: m a l e s L b f r a i l other species were f r e q u e n t l y observed to make c o p u l a t i o n attempts w i t h un-r e c e p t i v e females. C_. wileyae males could be induced to attempt c o p u l a t i o n w i t h unreceptive females by p l a c i n g both sexes i n the same container and p l a y i n g back female s i g n a l s from a tape. In C_. dakotensis the o r i e n t a t i o n of males seems to be completely dependent upon a u d i t o r y s t i m u l i because they were never seen to attempt c o p u l a t i o n with a non-singing female present i n the c o n t a i n e r , regardless of playbacks: i n a l l such cases they t r i e d to f i n d the source of the female s i g n a l . Observations on a c t u a l mating i n t h i s species were unsuccessful owing to the f a c t t h a t females were r e c e p t i v e Table V. Distance f o r r e c o g n i t i o n of s i g n a l s of opposite sex i n some Cenocorixa. species i n sand l i n e d bathtub. Each specimen was te s t e d against 2 5 s i g n a l s at each distance shown and p o s i t i v e r e a c t i o n s are shown i n per cent of t o t a l number of s i g n a l s tested f o r each species. No s i g n i f i c a n t d i f f e r e n c e s were found between the i n d i v i d u a l s of any one species. - = distance not t e s t e d . Species/sex t e s t e d b i f i d a o* b i f i d a ? utahensis o* b l a i s d e l l i cf wileyae o* wileyae ? e x p l e t a o* Number of specimens tested 2 2 3 3 3 2 2 5 7.5 100 100 100 100 100 tested (cm) 10 1 5 20 2 5 3 0 40 5 0 60 0 0 - - - - - -0 0 - - - - - -100 - 100 8 5 - - -100 0 0 - - - - -100 - 100 0 0 - - -66 0 0 - - - - -100 — 100 - 100 100 54 0 H Table VI. S p e c i f i c d i f f e r e n c e s observed i n mating behavior of Cenocorixa males. Explanations: 1) = females r e c e p t i v e only i n darkness; 2) = mounting s i g n a l observed, o r i g i n unknown. Species b i f i d a k u i t e r t i andersoni utahensis dakotensis Number of copulations observed su c c e s s f u l unsuccess-f u l Stimulus r e l e a s i n g Response to Mounting Remarks mating behavior i n . s i g n a l s of process 6 0 5 0 35 15 20 5 0 males v i s u a l & au d i t o r y v i s u a l & ? aud i t o r y & v i s u a l a u d i t o r y & v i s u a l a u d i t o r y only other males a g o n i s t i c & answer a g o n i s t i c & answer answer & a g o n i s t i c answer & a g o n i s t i c answer ? f a s t f a s t ? f a s t 2-step b l a i s d e l l i wileyae 6 15 20 a u d i t o r y & v i s u a l a u d i t o r y answer none f a s t slow 2) e x p l e t a 5 18 a u d i t o r y none f a s t H ro (& v i s u a l ?) o Table V I I . S p e c i f i c d i f f e r e n c e s observed i n mating behavior of Cenocorixa females. Number of cppulations as i n Table VI. Explanation: 1) = mounting s i g n a l of unknown o r i g i n observed. Species b i f i d a k u i t e r t i andersoni utahensis dakotensis b l a i s d e l l i wileyae e x p l e t a Response to males before c o p u l a t i o n or attempt Response to males during c o p u l a t i o n or attempt Remarks re c e p t i v e $$ unreceptive $$ answer s i g n a l s , escape, ago-remain s t a t i o n a r y n i s t i c or none answer s i g n a l s , ? escape or none answer s i g n a l s , none or escape remain s t a t i o n a r y answer s i g n a l s , none remain s t a t i o n a r y , (search ?) answer s i g n a l s , but none only i n darkness answer s i g n a l s , escape or none remain s t a t i o n a r y answer s i g n a l s , remain s t a t i o n a r y answer s i g n a l s remain s t a t i o n a r y none (even when male proceeds to precopula escape or none re c e p t i v e ?? passive passive rub male g e n i -t a l i a w i t h hind legs ? passive passive passive unreceptive $$ vigorous swimming, s u r f a c i n g , k i c k i n g vigorous swimming, d i v i n g under rocks, k i c k i n g swimming to surface, k i c k i n g vigorous swimming to surface , k i c k i n g press abdomen against 1) bottom, surface, k i c k i n g vigorous swimming and s u r f a c i n g when g e n i t a l contact i s t r i e d vigorous swimming, 1) s u r f a c i n g , k i c k i n g H ro H 122 (= answered to male s i g n a l s ) only i n darkness. However, t h i s i s q u i t e n a t u r a l because the experiments on d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of males showed t h i s species to be no c t u r n a l . The importance of the female s i g n a l i n a s s i s t i n g the male to l o c a t e the female was a l s o t e s t e d by p l a c i n g s e v e r a l unreceptive females together w i t h one r e c e p t i v e female i n the bathtub. In none of these experiments d i d the male attempt to copulate w i t h the unreceptive females a f t e r the r e c e p t i v e one s t r i d u l a t e d : immediately a f t e r the f i r s t answer of the r e -cept i v e female the male l o c a t e d the female and c o p u l a t i o n commenced. Thus, i n one experiment three C_. b l a i s d e l l i females 2 were s e t t l e d w i t h i n 1 cm when a male was introduced. The male happened to stop c l o s e to the females, and a f t e r a while i t produced a s i g n a l . The r e c e p t i v e female, s e t t l e d behind two unreceptive ones, s t r i d u l a t e d i n answer to the male s i g n a l . The male immediately ori e n t e d towards the group of females. The s i g n a l of the r e c e p t i v e female was s t i l l c o n t i n u i n g when the male passed the two unreceptive females, and without f u r t h e r s i g n a l s i t mounted the r e c e p t i v e female. Thus, i t seems obvious t h a t the female s i g n a l guided the male d i r e c t l y to the female. Further, by arranging an experiment w i t h r e c e p t i v e females of C_. b i f i d a and _C. expleta together, and i n t r o d -using males of e i t h e r species, i t .was observed that only i n t r a s p e c i f i c copulations occurred. When the r e c e p t i v e females answered the male c a l l and thus released the searching behavior i n males, the female s i g n a l very o f t e n s t a r t e d before the male s i g n a l was com-p l e t e d : the two s i g n a l s were p a r t l y overlapping. Further, i f the male d i d not produce more than one s i g n a l , the female u s u a l l y repeated i t s s i g n a l two to s i x times before ceasing to respond. Otherwise females were never observed to s t r i d -u l a t e spontaneously. This was checked with three C_. b i f i d a and two C_. wileyae females over one 24 hour p e r i o d i n each species i n a way s i m i l a r to the experiments on the d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y i n males, but no s i g n a l s were obtained. U s u a l l y the female d i d not search f o r the male, but remained s t a t i o n a r y . Only, i n one species, _C. utahensis, was one female observed to search f o r the male, but t h i s was i n a c u l t u r e t r a y , where the male had d i f f i c u l t i e s i n l o c a t i n g the female owing to echoes from the w a l l s . I t i s probable that the females would not search f o r males i n n a t u r a l c o n d i t i o n s . Unreceptive females showed a g o n i s t i c behavior towards s t r i d u l a t i n g males only i n C_. b i f i d a : i n other species they e i t h e r swam away (escaped) or showed no s p e c i a l behavior. In C_. wileyae the unreceptive females remained passive .even when the male mounted them, and rel e a s e behavior was not shown u n t i l the male attempted g e n i t a l contact. On the other hand, t h i s was a species where the males most often remained i n precopula (mounted the female, but d i d not t r y g e n i t a l contact) f o r a w h i l e . When a male mounted a r e c e p t i v e female, t h i s happened i n most species by a very f a s t movement and g e n i t a l contact 124 was obtained almost immediately. However, i n (J. utahensis the procedure seems to be completed i n two steps: the male mounts the female f i r s t q u i t e normally, but releases the female immediately and r i s e s a few m i l l i m e t r e s above the female, and s e t t l e s down again. In CJ. wileyae the procedure i s performed slowly and c a r e f u l l y compared to any other species. U s u a l l y the male stays I n precopula f o r a few seconds: the male clasps the female w i t h the f r o n t l e g s , but does not immediately i n i t i a t e g e n i t a l contact. S i m i l a r precopulatory behavior was observed i n other species a l s o , but only between a male and an unreceptive female: i f the female d i d not manage to drop the male from the c l a s p i n g p o s i t i o n a f t e r the f i r s t t r i a l of g e n i t a l contact, the p a i r o f t e n remained i n precopula, but as soon as the male t r i e d f u r t h e r g e n i t a l c o n t a c t s , the re l e a s e behavior of the female was i n i t i a t e d . During c o p u l a t i o n only CJ. utahensis females showed a s p e c i a l mating a c t i v i t y , by rubbing the g e n i t a l r e g i o n of the males w i t h t h e i r hind l e g s . This rubbing was not observed to produce any sounds. Females of a l l other species seemed to stay passive. However, the o r i g i n of the mounting s i g n a l observed i n _C. b l a i s d e l l i and C_. expleta i s unknown, and might be produced by the females. The release behavior of unreceptive females of a l l species was observed to be g e n e r a l l y s i m i l a r . D i s s e c t i o n of r e c e p t i v e and unreceptive females showed t h a t the r e c e p t i v e females always had chorionated eggs both i n the ovaries and i n the l a t e r a l oviducts. Unreceptive females which had been kept i s o l a t e d from males f o r s e v e r a l days, d i d not have any chorionated eggs i n the l a t e r a l o v i -ducts, and at the most had only a few chorionated eggs i n the o v a r i e s : u s u a l l y the ovaries were obviously immature. 126 d) Species r e c o g n i t i o n A s e r i e s of playback experiments was undertaken wherein the response of one species was t e s t e d against s t r i d u l a t o r y s i g n a l s of the same, and then against s i g n a l s of a l l other species. S i g n a l s of both males and females were used and a c t i v e males and r e c e p t i v e females were u t i l i z e d i n order to determine the a b i l i t y of the specimens to d i s c r i m i n a t e the s i g n a l s of t h e i r own species, i . e . answer to the r i g h t s i g n a l s . Tables V I I I - XI summarise the r e s u l t s of these experiments. According t o t a b l e V I I I males of C_. b i f i d a , C_. k u i t e r t i , C_. andersoni, C_. b l a i s d e l l i , and C_. wileyae r e a d i l y answered to the male c a l l s of t h e i r own species. C_. b i f i d a and e s p e c i a l l y C_. wileyae a l s o answered some other s i g n a l s , while _C. utahensis, _C. dakotensis, and _C. expleta. were not found to respond very much to any signal.. „ I t should be noted that males of c e r t a i n species some-times produce a complete s i g n a l or the f i r s t p a r t of the s i g n a l alone, and thus these p o s s i b i l i t i e s were t e s t e d separately. D i f f e r e n c e s were found i n the response of males and females to these separate s i g n a l s . For instance C_. utah-ensis and e s p e c i a l l y _C. andersoni males responded more r e a d i l y to the f i r s t p a r t of the c o n s p e c i f i c male s i g n a l / while females of the same species required a complete con-s p e c i f i c male s i g n a l i n order to respond (Tables V I I I and X). On the other hand, i n £. b l a i s d e l l i and _C. wileyae both males and females responded more r e a d i l y to a complete"con-s p e c i f i c male s i g n a l , and C_. k u i t e r t i males e q u a l l y w e l l 127 to both types of c o n s p e c i f i c male s i g n a l s . Further, i n cases when males of some species responded to s i g n a l s of other species by s t r i d u l a t i n g , i t was a l s o observed that when mixed c u l t u r e s w i t h s e v e r a l species were arranged, i n t e r -s p e c i f i c a g o n i s t i c behavior occurred f r e q u e n t l y . Table IX shows the response of the males to various female c a l l s . A response was obtained every time a male was exposed to;the c a l l of a c o n s p e c i f i c female. Further, males of some of the species a l s o f r e q u e n t l y responded to s i g n a l s from a female of another species. However, observations of the male specimens during these i n t e r s p e c i f i c playback experiments showed th a t the only s i g n a l s inducing searching behavior of the males were s i g n a l s from a c o n s p e c i f i c female. In experiments c a r r i e d out i n the sand l i n e d bathtub i t was observed that t h i s searching behavior i n a l l species always i n v o l v e d more or l e s s d i r e c t movement to the source of the female s i g n a l : only i f the meeting of the sexes was prevented (by p l a s t i c screen or i n playback experiments) was swimming i n c i r c l e s observed. In c o n t r a s t , the a g o n i s t i c behavior of males always i n v o l v e d a c i r c l i n g swimming movement. Table X shows the r e s u l t s of experiments t e s t i n g the response of females to the s t r i d u l a t o r y s i g n a l s of males. In a l l cases the females responded to s i g n a l s from a con-s p e c i f i c male. In a few cases i n v o l v i n g species p a i r s o c c u r r i n g a l l o p a t r i c a l l y (_C. b i f i d a - C_. andersoni, _C. dakotensis -C_. wileyae) response to a male s i g n a l s of another species was recorded. In the case of _C. b i f i d a females, they answered the f i r s t p a r t of a C_. andersoni male s i g n a l , but d i d not 128 respond to a complete s i g n a l . On the other hand, C_. wileyae females responded every time to C_. dakotensis male s i g n a l s . However, even i f these species should occur s y m p a t r i c a l l y , the r e s u l t s do not n e c e s s a r i l y mean a breakdown of the s t r i d -u l a t o r y i s o l a t i n g mechanism, since the males i n v o l v e d d i d not search f o r a mate, although they o c c a s i o n a l l y answered the wrong female c a l l s (Table I X ). F i n a l l y , when female s i g n a l s were t e s t e d against females, only C_., expl e t a responded (Table X I ) . Cenocorixa species occur s y m p a t r i c a l l y w i t h other C o r i x i d a e , and where p o s s i b l e , the s i g n a l s of these other taxa were a l s o tested ( f o r d e s c r i p t i o n of the s i g n a l s of these other taxa, see Appendix I I ) . The t e s t s showed th a t some Cenocorixa males answered the s i g n a l s from other C o r i x i d a e , but the few females which could be t e s t e d d i d not respond (Table X I I ) . The observed response of Cenocorixa males i s apparently i n connection w i t h a g o n i s t i c behavior. The question of how c o r i x i d s d i s t i n g u i s h the s i g n a l s of c o n s p e c i f i c males or females from s i g n a l s of other species was not studied i n d e t a i l i n the present work. However, a few observations were made on t h i s phenomenon. In C_. andersoni the female c a l l c o n s i s t s of one to three s i m i l a r pulse groups which are separated from each other by short (1-2 seconds) i n t e r v a l s . When only one pulse group was played back to the males, a searching response was observed only i n about 25 per cent of the males, but when a sequence of two or three pulse groups was played back, a searching response i n 100 per cent of the t e s t e d males was observed. S i m i l a r l y , C_. 129 ex p l e t a males responded to c o n s p e c i f i c female s i g n a l s which are composed of pulse groups, but d i d not respond to s i g n a l s composed of continuously repeated pulses which had the same pulse r a t e as the c o n s p e c i f i c female c a l l s . I t seems p o s s i b l e that the temporal p a t t e r n of pulses i s the c r i t i c a l f a c t o r i n species r e c o g n i t i o n i n Cenocorixa. 130 Table V I I I . Response of Cenocorixa males to playback, of male s i g n a l s . Each species was t e s t e d 25 times f o r each s i g n a l . Symbols: 0 = 0r20 per cent response by answering; + = 20-40 per cent response; * = 40-60 per cent response; ** = 60-80 per cent response; *** = 80-100 per cent response. S i n g l e u n d e r l i n i n g = species sympatric; double u n d e r l i n i n g = con-s p e c i f i c s i t u a t i o n . I f two f i g u r e s appear i n the same species entry, the upper one represents the f i r s t p a r t of the s i g n a l alone used as a stimulus and the lower one a complete s i g n a l used as a stimulus. Species responding b i f i d a k u i t e r t i andersoni utahensis wileyae e x p l e t a Ti cu -p CQ CU - P <H CQ O £ CU in 6 CU -H -Q O M CU 3 ft S CQ Male signal--.used as stimulus 5 5 5 dakotensis 5 b l a i s d e l l i CO Ti •H •H .Q 0 + 0 0 5 + + 0 •H +3 fH CU - P •H id 0 0 *** + 0 + 0 0 0 + -X-0 + •H o CQ CU Ti CO 0 0 0 0 0 0 0 + 0 0 + 0 0 CQ •H CQ a cu & ti -p 0 0 + + 0 0 + 0 CQ •H CQ C 0 +^  o M ti Ti 0 + + + 0 0 0 •H H H CU CQ •H CO 0 + 0 0 0 0 0 0 0 •** *** 0 0 0 0 cu CO I>> 0 H •rl 0 0 0 0 + + + 0 0 0 + + *** + 0 CO - P 0 H ft X 0 0 0 0 0 0 0 131 Table IX. Response of Cenocorixa males to playback of female s i g n a l s . Explanations as i n Table V I I I , but - = not t e s t e d . Species responding b i f i d a k u i t e r t i andersoni utahensis dakotensis b l a i s d e l l i wileyae e x p l e t a CD -p CO CD -p Female s i g n a l used as stimulus co •H CQ CO •rH H o •H •H CO H CD -P o CO a CD CD ti fn a ^ CO CD Td ti -P CD •H -P co >> CD £2 O •H -P CD o •H 0) H CD CH •rH CO i d ti H ft d ft •H a -P ti H •H X co 3d ti 3 X2 CD 5 5 5 5 5 5 5 5 0 0 0  + + + 0 + + 0 0 •X--X-* •* 0 0 0 0 0 *** 0 + + 0 + 0 ** + 0 *** 0 0 + 0 + 0 0 + + 0 + *** 132 Table X. Response of Cenocorixa females to playback of male s i g n a l s . Explanations as i n Table V I I I , but - = not t e s t e d . Species responding b i f i d a k u i t e r t i andersoni utahensis dakotensis b l a i s d e l l i wileyae e x p l e t a co fl 0 S •r-i O CD ft CO 3 2 4 4 5 3 Male s i g n a l used as stimulus CO •H C H •H CO •H rH o •• fl • H CO H -P o co fl 0 0 cd H T d CO r H co fl 0 T d CO • p CD CD CD r H 0 -P CO >i 0 n -P •H -P 0 X! O •rH 0 H & CO C H •rH T d cO i d CO H ft 3 CD •H d fl P> CO r?H •r-i X s - p J D i d CO d -a £2 0 4 + •* 0 0 0 0 0 . + 0 0 0 0 0 0 0 0 0 •X- 0 0 0 ' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 + 0 + 0 0 0 0 0 0 0 0 + + 0 0 0 0 0 0 * * ** 0 0 0 + 0 0 0 0 0 0 0 + 133 Table XI. Response of Cenocorixa females to playback, of female s i g n a l s . Explanations as i n Table V I I I , but - = not t e s t e d . Species responding Td CD -p CO CD •P b i f i d a k u i t e r t i andersoni 3 utahensis 2 dakotensis 4 b l a i s d e l l i 4 wileyae 5 e x p l e t a 3 Female s i g n a l used as stimulus CO •H, (H co CO •H H o fl •H fl •H co r-l CD -p o CO fl CD CD CO !H a CO fn co CD Td CO - P CD -H TJ CD H CD - P CO >i CD Jd O •H - P CD • f l . o •H CD H & CD CH •H cci id CO H ft d ft •H d fl - P CO H •H X a co id CO d Td id £ CD 4 0 0 0 0 0 -X- 0 0 _0_ _0_ 0 _0_ 0 =£= 0 o o 0 = ± = _ 0 _ 0 0 0 * 0 0 + 0 + 0 0 0 0 + 0 0 0 + 0 o o o o o * * * -Table X I I . Response of Cenocorixa spp. to playback of s i g n a l s of sympatric species of other Corixidae. Each species was tested 25 times f o r each s i g n a l . Explanations as i n Table V I I I , but - = not sympatric, therefore not t e s t e d ; $ - occurs i n same general area, but was not found i n same water body. Cenocorixa spp/sex responding b i f i d a cf b i f i d a ? k u i t e r t i cf andersoni cf utahensis cf dakotensis cf dakotensis $ b l a i s d e l l i cf wileyae cf wileyae ? exple t a cf Number of specimens tested 5 2 10 5 3 1 2 5 10 5 5 Signals used f o r stimulus: C a l l i c o r i x a v u l n e r a t a cf 0 0 0 C a l l i c o r i x a audeni o* * 0 0 0 0 0 0 C a l l i c o r i x a t e t o n i cf + 0 0 Sigara omani cf 0 0 * * * 0 Sigara n e v a d -ensiscC 0* 0* 0* 0* Sigara nevad-ensis? 0* 0* 0* 0* C o r i -s e l l a t a r -s a l i s c C 0 0 0 0 0 0 0 H UJ 135 6. Geographic d i s t r i b u t i o n and notes on ecology and h a b i t a t s of the species The species r e c o g n i t i o n experiments i n d i c a t e t h a t s t r i d -u l a t i o n serves as an i s o l a t i n g mechanism between the species. However, t h i s i s o l a t i o n may not always be 100 per cent e f f e c -t i v e . Thus, i t would be n a t u r a l to expect other i s o l a t i n g mechanisms to e x i s t as w e l l . In order to c l a r i f y these, the geographic d i s t r i b u t i o n of the species was reviewed, and notes on ecology and h a b i t a t s were made. a) Data on d i s t r i b u t i o n and notes on ecology Data on general d i s t r i b u t i o n of the species of the genus Cenocorixa are published only i n Hungerford (1948). Some add-i t i o n a l i n f o r m a t i o n can be found i n Hungerford (1956), Lans-bury (1955; I 9 6 0 ) , Sparrow (1966), Brooks and K e l t o n (1967), and Scudder (1969 a). In the f o l l o w i n g l i s t , the d i s t r i b -u t i o n a l records are according to Hungerford (1948), and other authors are only mentioned i f t h e i r records change the range of the species. However, i n every case the provinces or s t a t e s where the species were obtained f o r the present study are mentioned s e p a r a t e l y ( f o r more d e t a i l s see Appendix I ) . Thus the known d i s t r i b u t i o n of the species i s as f o l l o w s : C. b i f i d a : CANADA: B r i t i s h Columbia, A l b e r t a , Sas-katchewan, Manitoba. USA: C a l i f o r n i a * , Idaho, Utah, Wyoming, Montana, North Dakota, Colorado, Minnesota, Rhode I s l a n d * * . * Lauck, D.R.j; (personal communication): The. specimens reported from C a l i f o r n i a belong e i t h e r to C_. k u i t e r t i or C_. utahensis. **•Rhode I s l a n d i s way out from the general d i s t r i b u t i o n a l area of the species and the re p o r t i s probably a mistake. 136 Scudder (1969 a) a l s o r e p o r t s Washington. For the present study the species was obtained from B r i t i s h Columbia, A l b e r t a , and Utah ( F i g . 5 4 ) . The species seems to occur i n freshwater of moderately s a l i n e lakes and ponds i n the i n t e r i o r p l a t e a u and p r a i r i e s . According to Scudder (1969 a) breeding was observed i n water bodies w i t h c o n d u c t i v i t y from 38.6 to 17688 micromhos/cm at 25°C. The l i m i t s f o r s u c c e s s f u l breeding during f i e l d work of 1969 were observed to be between 50 and 13200 micromhos/ cm at 25°C. C_. k u i t e r t i : USA: C a l i f o r n i a , Utah. The l a t t e r record (Wasatch Mountains, Duchesne), based on one male and two females (Hungerford, 1948), i s probably a m i s - i d e n t i f i c a t i o n : the species i s o f t e n very d i f f i c u l t to separate from C_. b i f i d a ( c f . Appendix I ) . I have found 0. b i f i d a , but not C_. k u i t e r t i i n the Wasatch Mountains area. During the present study _C. k u i t e r t i was only found at the type l o c a l i t y i n C a l i f o r n i a ( F i g . 54)..This l o c a l i t y i s i n the high s i e r r a at a l t i t u d e s of 3300 m, and the species i n h a b i t s small freshwater ponds and creeks of a sub-alpine meadow (measured c o n d u c t i v i t y of the water 60 micromhos/cm at 25°C). _C. andersoni: USA: Washington, Oregon [Hungerford (1956) r e p o r t s the same States f o r _C. m a l k i n i Hungerford, which i s a synonym of C_. andersoni ( c f . Appendix I ) ] . Lansbury ( i 9 6 0 ) reported the species from B r i t i s h Columbia, both under i t s c o r r e c t name and under the name C_. downesi Lansbury, the l a t t e r being a synonym of the former ( c f . Appendix I ) . In the present study the species was found i n B r i t i s h Columbia 1 3 7 and Washington ( F i g . 5 5 ) . The species occurs i n freshwater ponds ( c o n d u c t i v i t y 4 8 5 micromhos/cm or below at 25°C) i n the lowland areas between t h e . P a c i f i c coast and the Coast Range mountains. _C. utahensis: CANADA: B r i t i s h Columbia, A l b e r t a , Mani-toba. USA: Oregon, O'Calif o r n i a , Idaho, Nevada, Utah, A r i z o n a , New Mexico, Colorado, Texas, Kansas, North Dakota, South Dakota, Iowa. Brooks and K e l t o n ( 1 9 6 7 ) report a l s o Sas-katchewan. In a d d i t i o n to Hungerford ( 1 9 4 8 ) , a l s o Lansbury ( i 9 6 0 ) and Sparrow ( 1 9 6 6 ) report the species from B r i t i s h Columbia. However, i n the c o l l e c t i o n s • o f the U n i v e r s i t y of B r i t i s h Columbia a l l the specimens i d e n t i f i e d as _C. utah-ensis from B r i t i s h Columbia belong to _C. b i f i d a . I t seems that the records of C_. utahensis from B r i t i s h Columbia are based on m i s - i d e n t i f i c a t i o n s and the species does not occur • i n t h i s province. In the present study the species was found i n A l b e r t a , Washington, and Utah (Fig.. 5 5 ) . The species, was not abundant In any of the studied areas, s c a t t e r e d specimens o c c u r r i n g both i n small and l a r g e water bodies i n the i n t e r i o r p l a t e a u and p r a i r i e s , o f t e n i n i r r i -g a t i o n r e s e r v o i r s . C o n d u c t i v i t y of the water v a r i e d between 3 1 0 and I67O micromhos/cm at 25°C. _C. dakotensis: CANADA: North-Western T e r r i t o r i e s , A l b e r t a , Saskatchewan, Manitoba. USA: Minnesota, I l l i n o i s , North Dakota, South Dakota. Lansbury ( 1 9 5 5 ) a l s o reports Iowa. In the present study the species was obtained from A l b e r t a ( F i g . 5 6 ) . The species was taken i n the spri n g of 1 9 7 0 i n shallow 138 ponds wi t h c o n d u c t i v i t y of the water between I IOO-I67O micromhos/cm at 25°C In August 1970 the species had d i s -appeared from these ponds, and c o n d u c t i v i t y of the water from the pond where the species was most abundant i n the s p r i n g , had increased from 1420 to 1880 micromhos/cm at 25°C. However, i t does not seem l i k e l y t hat the small change i n the c o n d u c t i v i t y could have caused the disappearance of the species because there were s e v e r a l ponds wi t h lower c o n d u c t i v i t y i n the v i c i n i t y , but C_... dakotensis was not detected. C. b l a i s d e l l i : USA: C a l i f o r n i a . Lansbury ( i 9 6 0 ) reports the species from B r i t i s h Columbia under the name C_. colum-b i e n s i s Lansbury. For the present study the species was obtained from B r i t i s h Columbia and C a l i f o r n i a ( F i g . 5 6 ) . The species seems to favor temporary or semipermanent ponds, but i s a l s o found i n l a r g e r , more permanent water bodies and a r t i f i c i a l park ponds. The l o c a t i o n of every pond where the species was found, was l e s s than two kilometres from the P a c i f i c c o a s t l i n e . However, the water was always f r e s h ( c o n d u c t i v i t y 215 micromhos/cm or l e s s at 25°C), although at l e a s t some of the studied water bodies occa-s i o n a l l y must r e c e i v e s a l t spray 'from the ocean. The species was not found i n ponds of t r u l y s a l i n e environments, but Scudder (unpublished) has exper i m e n t a l l y shown that i t sur-v i v e s long periods i n r a t h e r high s a l i n i t i e s . C_. wileyae: USA: Washington, Oregon, C a l i f o r n i a , Nevada, Utah, A r i z o n a , New Mexico, Colorado. During the present study the species was obtained from Washington, Oregon, C a l i f o r n i a , 139 Nevada and Utah ( F i g . 5 7 ) . The species was found i n the hi g h s i e r r a up to a l t i t -udes of 3300 m, and i n the i n t e r i o r p l a t e a u at a l t i t u d e s beginning at.300 m. C o n d u c t i v i t y of the water was u s u a l l y between 60-300 micromhos/cm at 25°C, but i n one l o c a t i o n where the species was very abundant, a c o n d u c t i v i t y of 85OO micromhos/cm a t 25°C was measured. C_, e x p l e t a : CANADA: Saskatchewan, Manitoba. USA: North Dakota, Colorado. Lansbury ( i 9 6 0 ) reports the species from B r i t i s h Columbia, and Edmondson (1966) from Washington. In the present study the species was obtained from B r i t i s h Columbia and Washington, w i t h one specimen a l s o from A l b e r t a ( F i g . 5 7 ) . The species favors higher s a l i n i t i e s than any other Cenocorixa species. Scudder (1969 a) repo r t s breeding i n lakes w i t h c o n d u c t i v i t i e s between 599O-2890O micromhos/cm at 25°C. The data c o l l e c t e d during the summer of 1969 showed c o n d u c t i v i t i e s between 5720-17540 f o r the lowest and highest values i n LB2 ( F i g . 3 6 ) , but up to 22300 micromhos/cm at 25°C was recorded i n Soap Lake, Washigton; i n a l l of these lakes breeding was observed to be s u c c e s s f u l . O c c a s i o n a l l y the species was caught i n almost freshwater l a k e s , but these specimens were obv i o u s l y immigrants because they had a com-p l e t e l y black mesonotum and were thus the f l y i n g form (Scudder, 1964); no l a r v a e were observed i n these l a k e s . Sympatric s i t u a t i o n s between the species are i n d i c a t e d i n Tables V I I I - X I . 140 F i g . 54. Known geographic d i s t r i b u t i o n of C. b i f i d a (squares) and _C. k u i t e r t i ( t r i a n g l e s ) . Open f i g u r e s r e f e r to published records, closed ones represent places where the species were obtained i n the present study. 141 F i g . 55. Known geographic d i s t r i b u t i o n of C_. andersoni (squares) and _C. utahensis ( t r i a n g l e s ) . Symbols as i n F i g . 54. 142 F i g . 56. Known geographic d i s t r i b u t i o n of _C. dakotensis (squares) and _C. b l a i s d e l l i ( t r i a n g l e s ) . Otherwise symbols as i n F i g . ^k. 143 144 b) Notes on e c o l o g i c a l i s o l a t i o n i n sympatric s i t u a t i o n s In cases when two or more Cenocorixa species were found s y m p a t r i c a l l y , comparative observations were made on the ecology and h a b i t a t s of the species. Sympatric s i t u a t i o n s were studied i n the f o l l o w i n g areas: i ) B r i t i s h Columbia, P a c i f i c Westcoast: C_. andersoni and C_. b l a i s d e l l i . These two species do not l i v e c ontinuously i n the same ponds because of a p a r t i a l e c o l o g i c a l i s o l a t i o n : £. andersoni occurs mostly i n l a r g e r , constant water bodies, wh i l e C_. b l a i s d e l l i i s mostly found i n temporary rainwater ponds and semitemporary pools. A l s o , while C_. andersoni seems to occur on most of the lowland area between the coast and the c o a s t a l mountains, _C. b l a i s d e l l i was only found w i t h i n 1-2 kilometres of the c o a s t l i n e . Both species are found t o -gether only from l a t e f a l l u n t i l s p r i n g , i . e . during over-w i n t e r i n g . They were not found to breed i n the same ponds. i i ) B r i t i s h Columbia, i n t e r i o r p l a t e a u : C_. b i f i d a and _C. e x p l e t a . P a r t i a l e c o l o g i c a l i s o l a t i o n e x i s t s between these species since the two are found to breed i n d i f f e r e n t s a l i n i t y ranges: C_. b i f i d a favors only moderately s a l i n e waters w i t h c o n d u c t i v i t i e s up to 13200 micromhos/cm at 25°C; C_. e x p l e t a occurs i n s a l i n e lakes w i t h c o n d u c t i v i t i e s between 5700-22300 micromhos/cm at 25°C (upper l i m i t i s probably h i g h e r ) . In cases when the species were r e g u l a r l y found i n the same la k e (Barnes Lake - c o n d u c t i v i t y 7850 i n May, 13200 i n August, and Long Lake - c o n d u c t i v i t y 98OO i n May, 11600 i n August: F i g . 3 6 ) , a f u r t h e r d i f f e r e n c e was observed between the species: C_. b i f i d a was found mostly at the very edges of the 145 water body, i n s i d e reed beds, while C_. expleta stayed mostly i n somewhat deeper water outside reed beds. i i i ) Southern A l b e r t a , p r a i r i e s : C_. b i f i d a , C_. utahensis, _C. dakotensis, and _C. expl e t a . C_. expleta, does not u s u a l l y occur w i t h the other species s i n c e , as noted above, i t favors s a l i n e waters. In freshwater h a b i t a t s s t u d i e d , w i t h conduct-i v i t i e s up to 2080 micromhos/cm at 25°C, one s i n g l e specimen of C_. e x p l e t a was found. C_. b i f i d a was found i n more s a l i n e waters than C_. utahensis and _C. dakotensis, and at conduct-i v i t i e s around 2000 micromhos/cm only C_. b i f i d a was found. D e t a i l e d study of s p e c i f i c d i f f e r e n c e s , however, remain un-solved because the area was v i s i t e d only twice. i v ) I n t e r i o r Washington: _C. utahensis, C_. wileyae, and C_. expl e t a . The three species were not found to occur i n the same water bodies, although they occur i n the same geographic area, w i t h i n 60 km radius of each other. E c o l o g i c a l l y C_. e x p l e t a was c l e a r l y separated from the two others by hig h s a l i n i t y of the h a b i t a t ( c o n d u c t i v i t y 22300 micromhos/cm at 25°C), while the other species were found i n f r e s h water. C_. wileyae and _C. utahensis populations were s c a t t e r e d and no c l e a r evidence of e c o l o g i c a l separation could be detected, although they were found i n separate ponds. v) C a l i f o r n i a , high s i e r r a : C_. k u i t e r t i and C_. wileyae. Both species were found i n f r e s h water ( c o n d u c t i v i t y 60 micromhos/cm at 25°C), but e c o l o g i c a l l y the ponds i n h a b i t e d by _C. wileyae seemed to be more eutrophic than the ones i n -habited by C_. k u i t e r t i . The l a t t e r species was a l s o found i n sl o w l y running water, while C_. wileyae was only obtained from 146 stagnant ponds. v i ) Utah: <C. b i f i d a and C_. wileyae; C_. utahensis and C_. wileyae. In Strawberry R e s e r v o i r , a few specimens of _C. wileyae were found amongst a l a r g e number of _C. b i f i d a , and i n S t a r v a t i o n Reservoir and i n southwestern Utah, s c a t t e r e d i n d i v i d u a l s of _C. utahensis and C_. wileyae were found together, No habitat, t.dif f erences were detected i n the short p e r i o d of observation; only one v i s i t to t h i s area was p o s s i b l e . 147 IV. DISCUSSION 1. Mechanism of sound production and a n a l y s i s of the s i g n a l s In a l l e a r l y papars on s t r i d u a l t i o n of Corixidae ( B a l l , 1846; Thomson, l8c;4; Carpenter, 1894; K i r k a l d y , 1901) the main question was the mechanism of sound production i n one European species, Sigara s t r i a t a ( L . ) , and i t was described i n c o r r e c t l y . The s t r i d u l a t o r y s i g n a l of S_. s t r i a t a i s very c l o s e to the s i g n a l of C_. wileyae*. [ f o r sound spectrograms of the s i g n a l of S_. s t r i a t a see. Finke ( 1 9 6 8 ) ] , with a simple m u l t i p u l s a t e f i r s t p a r t and a very loud second part composed of r e g u l a r pulse groups. M i t i s (1936) described the mechanism of s t r i d u l a t i o n i n S_. s t r i a t a as f o l l o w s : s t r i d u l a t o r y pegs on the f r o n t femora ; are rubbed against sharp edges of the head:about midway between the labium and the antennae. The f i r s t p a r t of the s i g n a l i s produced by a l t e r n a t i n g , the second part by s i m u l -taneous movements of the f r o n t l e g s : t h i s e x p l a n a t i o n was a l s o supported by Finke (1968). However, i n Cenocorixa the plectrum i s the m a x i l l a r y p l a t e , l o c a t e d p o s t e r i o r to the d o r s o l a t e r a l corner of the anteclypeus (terminology according to Parsons, 1965; 1966). According to specimens i n the c o l l e c -t i o n s of Dr. G. G. E. Scudder, S_. d o r s a l i s (Leach.), which i s very c l o s e l y r e l a t e d to S_. s t r i a t a , . and which a l s o has a very s i m i l a r s t r i d u l a t o r y s i g n a l ( H a s k e l l , 1961), has a m a x i l l a r y p l a t e s i m i l a r to the plectrum of Cenocorixa. This apparently f u n c t i o n s as the plectrum a l s o i n the genus Si g a r a (as w e l l _* Information of S_. s t r i a t a s i g n a l s based mostly on my own unpublished recordings made i n F i n l a n d and Sweden. 1 4 8 as i n other s t r i d u l a t i n g European C o r i x i n a e ) . Another d i f f e r e n c e between observations on European Cori x i n a e and Cenocorixa i s that only a l t e r n a t i n g movements of the f r o n t l e g s were observed during s t r i d u l a t i o n of the l a t t e r . According to spectrograms of s i g n a l s of S_. s t r i a t a (Finke, 1 9 6 8 ; Jansson, unpublished) i t seems u n l i k e l y that _S. s t r i a t a u t i l i s e s simultaneous movements of the f r o n t l e g s : d e t a i l e d spectrograms do not show any doubling of impacts. Further, Finke ( 1 9 6 8 ) a l s o claims that C a l l i c o r i x a praeusta ( F i e b . ) , another European species, produces the f i r s t p a r t of i t s s i g n a l by a l t e r n a t i n g and the second part by si m u l -taneous movements of the f r o n t l e g s . The s i g n a l of t h i s species (Finke, 1 9 6 8 ; Jansson, unpublished) i s very much l i k e the s i g n a l s of some other C a l l i c o r i x a species [_C. prod-ucta (Reut.) i n Europe, C_. audeni Hungfd. i n North America], and a l s o resembles very much the s i g n a l s of Cenocorixa an-dersoni and _C. utahensis, and I have not observed any si m u l -taneous movements of the f r o n t legs during s t r i d u l a t i o n of these species. In f a c t , I have f i l m e d the s t r i d u l a t i o n of C a l l i c o r i x a producta (unpublished) w i t h a high speed camera, and the f i l m shows only a l t e r n a t i n g movements of the f r o n t l e g s . In the genus Micronecta (Micronectinae), the mechanism of s t r i d u l a t i o n i s b e l i e v e d to be ass o c i a t e d w i t h the abdom-i n a l s t r i g i l ( M i t i s , 1 9 3 6 ; Southwood and Leston, 1 9 5 9 ) . Most species:, of Corixinae a l s o have a s t r i g i l , but i t seems to f u n c t i o n f o r attachment to the female during c o p u l a t i o n (Larsen, 1 9 3 8 ) . In two of the species studied i n the present 149 work., _C. b l a i s d e l l i and C_. e x p l e t a , f a i n t s t r i d u l a t o r y s i g n a l s were observed during the f i r s t few seconds of succ-e s s f u l c o p u l a t i o n s . The mode of production of these sounds was not detected, but a p o s s i b i l i t y e x i s t s t h a t the s t r i g i l would have a r o l e i n production of these sounds: p l a c i n g the s t r i g i l i n t o i t s proper p o s i t i o n could produce these sounds. D e t a i l e d spectrograms on the s t r u c t u r e of the pulses i n s t r i d u l a t o r y s i g n a l s of Corixidae have not been published p r e v i o u s l y . However, s e v e r a l s t u d i e s on Orthoptera ( e . f . H a s k e l l , 1961; Dumortier, 1963 b) have shown that each impact of a pulse i s equivalent to one s t r i k e of one tooth of the pars s t r i d e n s on the plectrum (when one pulse i s de-f i n e d as a completed movement of the s t r i d u l a t o r y apparatus, which i s the usual d e f i n i t i o n i n b i o a c o u s t i c a l s t u d i e s ; t h i s being i n c o r r e c t In p h y s i c a l terms). The d i f f e r e n c e between the pars s t r i d e n s i n Orthoptera and C o r i x i d a e i s t h a t Orth I-opterans u s u a l l y have one s i n g l e row of t e e t h or d e n t i c l e s while C o r i x i d a e have s e v e r a l rows of s t r i d u l a t o r y pegs. How-ever, i t seems very l i k e l y t . t h a t each impact i n the d e t a i l e d a n a l y s i s of the s i g n a l s of Cenocorixa i s produced by one peg row. M i t i s (1936) found a c o r r e l a t i o n between the thickness of the s t r i d u l a t o r y pegs and the loudness of the s i g n a l s of d i f f e r e n t species. In the present study, observations on the two sexes of each species suggest that the s t r u c t u r e of the plectrum could a l s o a f f e c t the amplitude of the s i g n a l s . The s i g n a l s of Cenocorixa were found to be species s p e c i f i c . S i m i l a r l y , i n previous p u b l i c a t i o n s ( M i t i s , 1936; 150 Leston, 1955) s i g n a l s of various c o r i x i d s have, been found to be species s p e c i f i c , but owing to i n s u f f i c i e n t t e c h n i c a l apparatus the exact d i f f e r e n c e s were not shown u n t i l i n Finke' s (.1968) paper. In t h i s paper, Finke (1968) published sound spectrograms and o s c i l l o g r a m s of s i g n a l s of Sigara  s t r i a t a and C a l l i c o r i x a praeusta, and the d i f f e r e n c e s between the species appear to be i n the temporal p a t t e r n of pulses and the pulse r e p e t i t i o n r a t e . The main frequency area of the sound i n both species i s approximately the same as i n Cenocorixa (3-5 kc/sec), but Finke (1968) obtained a l s o some higher overtones ("Oberwelle" i n German) at 6-10 and 9-15 kc/sec and over. This seems to be an a r t i f a c t , because I was able to make s i m i l a r overtones by overloading reproduce power of the spectrograph ( F i g . 5 8 ) . The d i f f i c u l t y i n a n a l y s i n g s i g n a l s w i t h short pulses i s that the i n d i c a t o r meter of the spectrograph does not have time to show the true reproduce amplitude of the peaks of the very short impulses and so a c c i d e n t a l overloading i s not detected [ c f . .Andrieu (1963): measuring the sonic l e v e l ] . The f a c t t h a t overtones are a r t i f a c t s was demonstr-ated by f i l t e r i n g some s i g n a l s w i t h a sound and v i b r a t i o n analyser type 155^ A (General Radio Co., Mass., U.S.A.), so that only the higher frequencies at 11-15 kc/sec were allowed through, and then a n a l y s i n g the f i l t e r e d sound. The r e s u l t showed no sounds at these frequencies, and i n t h i s experiment both the input and reproduce l e v e l could be much higher than w i t h normal s i g n a l , because the p o s s i b i l i t y of overloading e f f e c t s of the lower frequencies was e l i m i n a t e d . 151 — ^ ••••—4—^4—-T-^-•2 .4 6 S E C O N D S F i g . 5 8 . Example of a r t i f a c t s created by improper a n a l y s i s of a Cenocorixa s i g n a l : sound spectrogram of one pulse group of a C.. expleta male s i g n a l analysed by overloading reproduce power of the spectrograph (readings of the VU-meter at peaks of the s i g n a l were 0, mark, l e v e l 7). A l l sounds appearing above 6 k.c/sec are a r t i f a c t s . Note th a t the f i r s t three pulses are f a i n t e r i n amplitude than the l a s t two: the stronger the sound, the more a r t i f a c t s are created. 15n CO 10-M 5 152 Finke (1968) may a l s o have obtained overtones because she recorded the s i g n a l s i n a styrofoam container. In com-par i n g s i g n a l s recorded i n a styrofoam container to recordings made under n a t u r a l c o n d i t i o n s , I found styrofoam to change the frequency p a t t e r n of Cenocorixa s i g n a l s . Temperature was not u s u a l l y observed to have an e f f e c t on the temporal p a t t e r n of pulses of Cenocorixa s i g n a l s , but i t c l e a r l y a f f e c t s the pulse r a t e and, when a p p l i c a b l e , the pulse group r a t e , as w e l l as the s i g n a l l e n g t h . Finke (1968) has a l s o published some data on temperature e f f e c t on s t r i d -u l a t i o n of Sigara s t r i a t a , but t h i s was on dur.ationf ofv.pulse groups and pulse group i n t e r v a l s . Thus, a c t u a l observations on pulse r a t e s of Corixidae other than Cenocorixa species, are l a c k i n g . Walker (1962) has studied the e f f e c t of temperature on s i g n a l s of s e v e r a l species of c r i c k e t s . He s t a t e s that temperature a f f e c t s the pulse r a t e of c r i c k e t s i g n a l s i n a uniform way and the f o l l o w i n g g e n e r a l i s a t i o n s were made: i ) r a t e of change i n pulse r a t e with temperature i s constant; i i ) the higher the pulse r a t e at a given temperature, the greater the r a t e of change; i i i ) i f r e g r e s s i o n l i n e s are e x t r a p o l a t e d downward, they tend to converge at 4°C and 0 pulses per second. Gener a l l y these r u l e s a l s o seem to f i t i n Cenocorixa s i g n a l s . F i g s . 17-26 show that a graph where pulse r a t e i s p l o t t e d against temperature forms a s t r a i g h t l i n e , but as Walker (1962) f u r t h e r s t a t e s f o r c r i c k e t s , i f a d e v i a t i o n from a l i n e a r r e l a t i o n s h i p i s found i t w i l l be at the extremes 153 of temperature; pulse rates of Cenocorixa seem to be s l i g h t l y higher than expected at low temperatures. F i g . 59 summarises the r e g r e s s i o n l i n e s of Cenocorixa males, and t h i s shows that the r e g r e s s i o n l i n e s f o r the species w i t h high pulse r a t e are g e n e r a l l y the steepest. However, F i g . 59 a l s o shows that the r e g r e s s i o n l i n e s of Cenocorixa do not converge at 4°C and 0 pulse per second, but most of them (8 out of 13) seem to con-verge at about 9°C and 6 pulses per second. Regression l i n e s f o r female s i g n a l s were a l s o c a l c u l -ated i n most species, but owing to the small temperature range s t u d i e d the l i n e s are probably'somewhat biased. In C_. wileyae females, when more observations were made i n d i f f e r e n t temperatures, the r e g r e s s i o n l i n e i s very c l o s e to the general l i n e s of the males. This .would probably have been the case a l s o i n females of other species i f more m a t e r i a l had been a v a i l a b l e . S i g n a l d u r a t i o n p l o t t e d against temperature was shown to be n o n - l i n e a r i n Cenocorixa ( F i g s . 22-24). In any s i g n a l i t can be shown that i f the change i n the pulse r a t e w i t h temperature i s constant (= l i n e a r r e g r e s s i o n ) , and the number of pulses i n the s i g n a l i s constant, the d u r a t i o n of the s i g n a l does not change l i n e a r l y when the temperature changes. As an example the pulse r a t e of C_. b i f i d a male has a regres-s i o n l i n e of Y = -O.766 + 0 . 4 6 6 X . Pulse r a t e s at 10°C, 20°C, and 30°C on t h i s r e g r e s s i o n l i n e are 3.9, 8.6, and 13.2 pulses per second, r e s p e c t i v e l y , and average number of pulses per s i g n a l was observed to be 19.60 f o r the species. From these values, expected s i g n a l durations i n the above 154 10 20 3 0 T e m p e r a t u r e (°C) F i g . 59. Summary of the r e g r e s s i o n l i n e s of temperature e f f e c t on pulse r a t e i n Cenocorixa male s i g n a l s , a = _C. wileyae f a s t pulse r a t e ; b - C_. utahensis f a s t pulse rate;, c = C_. andersoni f a s t pulse r a t e ; d = (J. k u i t e r t i f a s t pulse r a t e ; e = _C. e x p l -eta f a s t pulse r a t e ; f = C_. utahensis slow pulse r a t e ; g = _C. andersoni slow pulse r a t e ; h = (J. k u i t e r t i slow pulse r a t e ; i = C. b l a i s d e l l i f i r s t p a r t pulse r a t e ; j = _C. dakotensis; k = C_. ex p l e t a slow pulse r a t e ; 1 = CJ. wileyae f i r s t p a r t pulse r a t e ; m = C. b i f i d a . 155 temperatures can be c a l c u l a t e d , and values of 5.0, 2.3, and 1.5 seconds are obtained. P i g . 60 A shows that these expected values form a curve which i s very c l o s e to the curve obtained from the a c t u a l observations on s i g n a l d u r a t i o n i n C_. b i f i d a . Thus, since the a c t u a l curve does not depart s i g n i f i c a n t l y from the c a l c u l a t e d values, i t shows that the number of pulses per s i g n a l (and apparently the temporal p a t t e r n of pulses as w e l l ) i s constant and independent of temperature. In F i g . 60 B s i g n a l d u r a t i o n graphs from a c t u a l observ-a t i o n s of a l l other Cenocorixa males are summarised, and i t i s seen that the general p a t t e r n f o l l o w s that of C_. b i f i d a ; s p e c i f i c d i f f e r e n c e s are apparently owing to d i f f e r e n c e s i n the pulse r a t e and average number of pulses per s i g n a l . Dumortier (1963 b) has a s i m i l a r observation on s i g n a l d u r a t i o n of Ephippiger p r o v i n c i a l i s (Yers.) (Orthoptera, T e t t i g o n i o i d e a ) : s i g n a l d u r a t i o n f o l l o w s a curve of hyper-b o l i c shape. Moore (1961) published sound spectrograms of s i g n a l produced b y a North American c o r i x i d , Hesperocorixa atopo-donta (Hungfd.). The main frequency area of these s i g n a l s i s 7-8 kc/sec, which i s c l e a r l y higher than i n any Cenocorixa s i g n a l . However, Moore kept the bugs i n a fingerbowl and recording was done by microphone protected from wetting by a f i s h swimbladder; these f a c t o r s p o s s i b l y changed the frequency of the sounds. Further, Moore (1961) s t a t e s that the pulse r a t e i n these s i g n a l s i s about 200 pulses per second, but t h i s apparently means the impact r a t e w i t h i n the pulses [ i f the pulse i s defined according to Dumortier (1963 c) 156 8-i 1 1 1 10 2 0 30 T e m p e r a t u r e (°C) F i g . 60 . Summary of temperature e f f e c t on s i g n a l d u r a t i o n i n Cenocorixa males. A: C. b i f i d a ; continuous l i n e = observed curve; broken l i n e = expected curve ( f o r more explanations see t e x t ) . B: observed curves; a = C_. wileyae; b = _C. expl e t a ; c = C_. utahensis; d = _C. dakotensis; e = _C. andersoni; f = C_. b l a i s d e l l i ( f i r s t p a r t of the s i g n a l o n l y ) ; g = C_. k u i t e r t i . 157 and the common concept i n b i o a c o u s t i c s ] . The s i g n a l s Moore (1961) observed were produced by a male specimen, and they d i d not have any apparent e f f e c t on other specimens (females) i n the v i c i n i t y . Moore observed f u r t h e r , that the sound was produced by rubbing the hind t i b i a e and t a r s i along the back of the specimen. Another species, S i g a r a g r o s s o l i n e a t a Hungfd., was observed to s t r i d -u l a t e i n a s i m i l a r way. This mechanism of sound production was a l s o observed by Finke (1968) i n studie s on Sig a r a s t r i a - t a , and i n t h i s case both males and females produced these sounds, but they were too f a i n t f o r s a t i s f a c t o r y r e c o r d i n g . In the present study a l l Cenocorixa species were observed to produce these sounds i n two ways: i ) a l t e r n a t e movements of hind l e g s , i i ) simultaneous movements of hind l e g s . A spectrogram of these sounds i s shown i n F i g . 30. No species s p e c i f i c i t y was observed and playback experiments u t i l i s i n g these sounds d i d not i n i t i a t e any response of males or f e -males. The bugs were observed to produce these sounds at any time of the year. These sounds appear to be a r e s u l t of cl e a n i n g movements and are not true s t r i d u l a t o r y s i g n a l s . The movements are apparently made to clean and rearrange the l a t e r a l abdominal h a i r s t h a t are important i n maintaining the a i r bubble between the wings and the abdominal dorsum f o r r e s p i r a t i o n (Popham, I96O; Parsons, 1970). Leston and P r i n g l e (1963) adhere to the o l d concept th a t the use of p a l a r pegs i n p o s s i b l e s t r i d u l a t o r y mechanism has not been disproven. They r e f e r to species which have not been observed to s t r i d u l a t e , and suggest that the s i g n a l s of these species might be too f a i n t to be recorded. In f a c t i t i s true that a l l species of Corixidae can o f t e n be observed to rub t h e i r palae against each other or the rostrum. How-ever, t h i s seems to be nothing more than a k i n d of c l e a n i n g a c t i v i t y , and sounds produced i n t h i s way would probably be f a r too f a i n t to have any s i g n i f i c a n c e i n the behavior of the bugs, e s p e c i a l l y when much more i n t e n s i v e sounds, prod-uced by the rubbing of the hind l e g s , appear to be s i d e -products of c l e a n i n g movements.and without b e h a v i o r a l s i g n i f i c a n c e . In Cenocorixa the use of p a l a r pegs i n s t r i d u l a t i o n i s impossible since only the males have these pegs, yet both males and females s t r i d u l a t e . In s i m i l a r genera, the p a l a r pegs of the males are used f o r c l a s p i n g the female during c o p u l a t i o n (Popham, 1961) : the pegs are placed under the curved l o n g i t u d i a l r i d g e of the l a t e r a l flange oh the female hemielytron; the two sexes are thus f i r m l y attached to one another, and are able to swim while i n copula. 159 2. L i f e c y c l e , sexual maturation, and s t r i d u l a t i o n D e t a i l e d study on l i f e c y c l e of four species was c a r r i e d out i n order to f i n d out how s t r i d u l a t i o n c o r r e l a t e s w i t h sexual m a t u r i t y i n the genus Cenocorixa. The study showed tha t i n the i n t e r i o r of B r i t i s h Columbia both C_. b i f i d a and C_. e x p l e t a commonly have a p a r t i a l second generation per summer. However, i n favourable circumstances a complete second generation and even a p a r t i a l t h i r d generation can be produced, as was shown of C_. • e x p l e t a i n the water body LB2. The f a i l u r e of Q. b i f i d a to produce more than one generation i n LB2 was apparently owing to i n c r e a s i n g s a l -i n i t y which during June and J u l y k i l l e d l a r v a e of the second generation. Hungerford (1948) states that i n general North American Corixidae produce one or two generations per summer, depend-i n g on temperature. Larsen (1938), C r i s p ( 1 9 6 2 ) , and Young (1965) have stud i e d the l i f e c y c l e s of s e v e r a l European C o r i x i d a e , and some species have been observed to have only one generation while others apparently produce a p a r t i a l second generation. S i m i l a r l y , Pajunen and Jansson (1969) and Pajunen (1970) observed a p a r t i a l second generation i n two species of c o r i x i d s l i v i n g i n rock pools i n the archipelago of southern F i n l a n d . However, n e i t h e r a completed second generation (as i n C_. andersoni i n the P a c i f i c Westcoast) nor a p a r t i a l t h i r d generation (C_. e x p l e t a i n LB2) have been reported p r e v i o u s l y . By comparing the temperature data on the lakes, s t u d i e d during the present work ( F i g s . 34-35), i t can be seen that LB2 g e n e r a l l y had a s l i g h t l y higher temper-160 ature than other l a k e s . Thus the p a r t i a l t h i r d generation i n C_. e x p l e t a occurred i n the warmest l a k e . P r i o r to the present work no d e t a i l e d study of the sequence of generations based on the phenology of the d i f f -erent l a r v a l i n s t a r s has been published. Apparently t h i s i s because the f i v e l a r v a l i n s t a r s are commonly found together i n the lakes throughout the summer, and the l a r v a e belonging to separate generations may be d i f f i c u l t to separate. The l a c k of i d e n t i f i c a t i o n keys f o r l a r v a e a l s o has not been conducive to such s t u d i e s . In the present work, however, i t was p o s s i b l e to i d e n t i f y the l a r v a e f o l l o w i n g Scudder (1966), and changes i n the r e l a t i v e numbers of d i f f e r e n t l a r v a l i n -s t a r s i n the samples were considered to be a r e l i a b l e I n -d i c a t o r i n p l a c i n g the l a r v a e i n t o proper generations. The sequence of generations was a l s o f o l l o w e d by studying the gonad development, the method used i n previous s t u d i e s on l i f e c y c l e s , but the l a r v a l study made more accurate s t a t e -ments p o s s i b l e . The study of the ovaries i n Cenocorixa showed th a t over-wintered females become s e x u a l l y mature soon a f t e r Ice break-up i n the i n t e r i o r of B r i t i s h Columbia, while at the coast m a t u r i t y i s reached i n March. In a d d i t i o n , C_. b i f i d a and _C. e x p l e t a were observed to f l y a c t i v e l y i n e a r l y May 1969, and C_. b l a i s d e l l i was found to f l y throughout the summer of 1970, when they were breeding. In c o n t r a s t , rock pool species of southern F i n l a n d have a short d i s p e r s a l p e r i o d before a t t a i n i n g sexual m a t u r i t y (Pajunen and Jansson, 1969). On the other hand, Young (1965) observed maturation of 161 females i n some species to occur before break-up i n England. Sexual maturation of females of the i n i t i a l p a r t .of the f i r s t g eneration i n Cenocorixa was observed to take about one week. S i m i l a r l y , Pajunen (1970) observed young females of C a l l i c o r i x a producta (Reut.) and A r c t o c o r i s a c a r i n a t a (C. Sahib.) to have chorionated.eggs w i t h i n a p e r i o d of 10-14 days. The l a t e r p a r t of the f i r s t generation i n Cenocorixa was observed to remain s e x u a l l y immature i n the i n t e r i o r of B r i t i s h Columbia. Both Young (1965) and Pajunen (1970), who made s i m i l a r observations, explained t h i s i n connection w i t h photoperiod. According to Young (1965) there i s no diapause i n the ovarian development because ad u l t females were observed to mature and l a y eggs i n the l a b o r a t o r y at a l l times, of the year when under experimental c o n d i t i o n s of 16 hours photo-p e r i o d and temperatures of 12-32°C. Further, he s t a t e s that the c o n t r o l of the i n i t i a l development of the ovaries prob-a b l y depends on photoperiodic e f f e c t . However, some of h i s own r e s u l t s are i n c o n s i s t e n t w i t h t h i s suggestion: He noticed f o r example-2in S i g a r a s c o t t i ( F i e b . ) , l i v i n g i n a lake w i t h wide shallow areas, that when the water l e v e l dropped some pools were formed along the l a k e : the f i r s t a d u l t s of the • f i r s t summer generation emerged more than two weeks e a r l i e r i n these pools than i n the lake i t s e l f . Further, he observed that i n none of the specimens i n the pools d i d ovarian matur-a t i o n take place, whereas i n the main lake i n e a r l y J u l y i t d i d ! In t h i s case at l e a s t , photoperiod could not have any-t h i n g to do wit h the d i f f e r e n c e i n the ovarian development. According to Pajunen (1970) a r r e s t e d ovarian development 162 appears i n e a r l y J u l y , which i s near the middle of the summer i n southern F i n l a n d . Further, he sta t e s that t h i s a r r e s t de-pends on photoperiod and th a t the adaptive value of ovarian a r r e s t i n t h i s p a r t i c u l a r case must l i e i n the l i m i t a t i o n of po p u l a t i o n s i z e : high reproductive c a p a c i t y of c o r i x i d s would boost the d e n s i t y of the populations beyond the l e v e l s of food resources i n the rock pool environment. The r e s u l t s of the present study showed d i f f e r e n c e s between the lakes i n the i n t e r i o r of B r i t i s h Columbia i n the timi n g of the a r r e s t i n ovarian development, but t h i s cannot r e f l e c t d i f f e r e n c e s i n the photoperiod: a l l lakes were w i t h i n a r e l a t i v e l y small geographic area, some of them only 1-2 kilometres from each other. Further, the l a k e where mature females were observed l a t e s t (LB2), was about 100 km f u r t h e r south than the others, and thus had a shorter photoperiod than the others throughout the summer. A d d i t i o n a l i n f o r m a t i o n i n support of t h i s c o ntention was obtained from Soap Lake, which i s l o c a t e d i n Washington, about 500 km south from the main study area. Here _C. e x p l e t a was found to be breeding as l a t e as 29 August 1969, and so here again the photoperiod i s shorter than i n the Cari'boo-Chilcotin area of B r i t i s h Columbia. Further, the experiment c a r r i e d out w i t h C_. b i f i d a on 8 and 16 hours photoperiod, showed that although not every female, at l e a s t some of the females i n both short and long photo-p e r i o d became s e x u a l l y mature at the same time i n l a b o r a t o r y c o n d i t i o n s , and thus independently of the photoperiod. When d i f f e r e n c e s observed i n the f i e l d studyii.n the ti m i n g of the a r r e s t i n ovarian development are compared 163 w i t h the p r o d u c t i v i t y of the l a k e s , a c l e a r c o r r e l a t i o n between the two i s found: i n low p r o d u c t i v i t y lakes a l l females were found to show ovarian developmental a r r e s t i n e a r l y J u l y , while i n high p r o d u c t i v i t y lakes reproductive females were observed u n t i l the end of J u l y . In lakes w i t h very h i g h p r o d u c t i v i t y , reproductive females were observed as l a t e as end of August. I t Is known that s t a r v i n g i n s e c t s do not develop eggs ( c f . Johansson, 1958; 1964), and thus i n low p r o d u c t i v i t y lakes i t seems probable that there i s a shortage of food. However, the exact food u t i l i s e d i n these low p r o d u c t i v i t y lakes i s unknown. In the high p r o d u c t i v i t y lakes both C_. b i f i d a and _C. e x p l e t a feed on Diaptomus s i c i l i s Forbes (Scudder, personal comm.), a copepod that i s absent from the low p r o d u c t i v i t y lakes (Scudder, 1969 b). Zwart (1965) suggests that almost any form of small l i v i n g animal would be adequate food supply f o r c o r i x i d s g e n e r a l l y , but at l e a s t i n some cases plankton animals seem to be p r e f e r r e d . I t i s most l i k e l y i n the S i g a r a  s c o t t i s t u d i e d by Young (1965), t h a t the specimens i n the pools cut o f f from the main l a k e , d i d not have an adequate food supply, and so remained s e x u a l l y immature,, whereas those i n the main lake were not short of food. Although Pajunen (1970) s t a t e s that ovarian a r r e s t prevents overpopulation i n rock pools, i t i s possible- t h a t because rock pools are not very productive water bodies, that i t i s the i n s u f f i c i e n t amount of food t h a t l i m i t s the siz:e_of populations by c u t t i n g o f f the development of the o v a r i e s . Thus, the present study suggests that photoperiod i s not 164 the c r i t i c a l f a c t o r i n the ovarian developmental a r r e s t i n the genus Cenocorixa. However, because the time of the a r r e s t i n t t h e high p r o d u c t i v i t y lakes does not c o i n c i d e w i t h any drop i n the a v a i l a b i l i t y of copepods, the l a c k of food may not be the only environmental f a c t o r envolved. The temper-ature records f o r the lakes show that the a r r e s t i s not c o r r e l a t e d w i t h an obvious.decrease i n temperature: temper-ature does not s t a r t to drop s i g n i f i c a n t l y u n t i l l a t e Sep-tember. Ovarian development i s probably i n f l u e n c e d by s e v e r a l f a c t o r s . Food supply, temperature, and photoperiod are f a c t o r s that may be important i n some in s t a n c e s , but t h i s aspect needs f u r t h e r i n v e s t i g a t i o n s . Sexual maturation of Cenocorixa males was observed to f o l l o w g e n e r a l l y the same p a t t e r n as the maturation of the females, but w i t h the f o l l o w i n g d i f f e r e n c e s : newly emerged males of the i n i t i a l p a r t of the f i r s t g eneration were sex-u a l l y mature at the time of emergence, and at l e a s t some of the overwintering males reached sexual m a t u r i t y i n l a t e f a l l , r a t h e r that e a r l y s p r i n g . Larsen (193<3) studied sexual matur-a t i o n of c o r i x i d s i n Sweden, and observed mature sperm i n the t e s t e s g e n e r a l l y during s p r i n g , but i n one species, Corixa dentipes Thorns., he a l s o detected sperm i n the t e s t e s i n September. On the other hand, Young (1965) s t a t e s that sperm i s formed during summer and autumn i n the overwintering males, stored i n the seminal v e s i c l e s u n t i l s p r i n g , and the te s t e s are i n a c t i v e i n the s p r i n g ! A l s o Pajunen (1970) claims that sperm was found i n the seminal v e s i c l e s of the l a t e summer specimens at the time when ovarian development i n 165 females was already a r r e s t e d . Neither Young (1965) nor Pajunen (1970) e x p l a i n the methods they adopted i n i n v e s t i g a t i n g the presence of sperm.) i n the seminal v e s i c l e s . However, with the squashing method used i n most of the present study, i t was not p o s s i b l e to observe sperm i n the seminal v e s i c l e s because i n Corixidae t h i s organ i s surrounded by a thick: l a y e r of connective t i s s u e : i f sperm e x i s t s i n the seminal v e s i c l e i t w i l l appear very s i m i l a r ttb the f i b r e s of the surrounding connective t i s s u e , and cannot be d i s t i n g u i s h e d . A l s o i n the t e s t e s them-selves there are some s t r u c t u r e s which appear very much l i k e mature sperm and some p r a c t i c e is- needed to d i s t i n g u i s h the presence of mature sperm. However, the r e s u l t s obtained w i t h the squashing method were checked by making s e r i a l s e c tions of the t e s t e s . Thus, although the seminal v e s i c l e s could not be studied i n squash p r e p a r a t i o n s , i t was shown that i f the t e t i c u l a r f o l l i c l e s d i d not c o n t a i n spermatids at t h e i r l a t e developmental stage ( F i g . 40 D), the seminal v e s i c l e s d i d not co n t a i n any sperm, and so the specimen was s e x u a l l y immature. In mature i n d i v i d u a l s a l l of the stages of spermato-genesis were c l e a r l y v i s i b l e i n the f o l l i c l e s i n the i n i t i a l p a r t of the f i r s t summer generation and l a t e f a l l i n s e c t s . In the overwintered specimens i t o f t e n was observed that mature sperm could not be detected i n the t e s t e s , but could be found i n the seminal v e s i c l e s i n the s e r i a l s e c t i o n s . How-ever, the presence of very l a r g e numbers of developing c y s t s w i t h a l l other stages of spermatogenesis i n d i c a t e that the t e s t e s were by no means i n a c t i v e as sta t e d by Young (1965). 166 I t would be more n a t u r a l to assume that the developing c y s t s f i l l e d the f o l l i c l e s and simply pushed the mature sperm i n t o the seminal v e s i c l e s . This i s a l s o supported by the f a c t that sometimes the sperm appeared to be s t i l l i n bundles i n the seminal v e s i c l e s i n the s e r i a l s e c t i o n s . Further, specimens studied i n l a t e summer, at the time of ovarian a r r e s t i n females, showed that the t e s t i c u l a r f o l l i c l e s were f i l l e d w i t h c y s t s i n stages of m e i b t i c d i v i s i o n and w i t h spermatids i n t h e i r e a r l y developmental stage ( F i g . 4 4 ) , but no f u r t h e r stages were found. At t h i s time, t h e r e f o r e , spermatogenesis was a l s o a r r e s t e d . The reason f o r the a r r e s t of spermatogenesis i s not e a s i l y explained. I t occurred simultaneously w i t h the a r r e s t of o 8 g e n e s i s i n females i n v a r i o u s lak.es. In general, however, i n s u f f i c i e n t nourishment i n male i n s e c t s does not u s u a l l y pre-vent sexual m a t u r i t y , but merely reduces the s i z e of the t e s -tes (Johansson, 1964). However, Geer (1967) and Geer and New-burgh (I97O) have shown w i t h Drosophila melanogaster that the development of mature sperm i s dependent upon d i e t a r y f a c t o r s . Thus, i t may be that the reasons f o r the a r r e s t of spermato-genesis are the same as f o r the a r r e s t of oogenesis, and at l e a s t p a r t l y owing to d i e t d e f i c i e n c i e s . I t i s not known why the males become s e x u a l l y mature i n l a t e f a l l while f e -males remain s e x u a l l y immature. Almost a l l previous studies on s t r i d u l a t i o n of Corixidae s t a t e t h a t s i g n a l s are produced only during the breeding season, i . e . s p r i n g and e a r l y summer ( M i t i s , 1936; S c h a l l e r , 1951; Leston, 1955; Southwood and Leston, 1959; Leston and 167 P r i n g l e , 1963; Finke, 1968). The only previous p u b l i c a t i o n mentioning s t r i d u l a t i o n during the f a l l i s Larsen (1938): C o r i x a dentipes was observed to s t r i d u l a t e i n September (Larsen a l s o detected sperm.'.in the te s t e s of t h i s species at the same time). In the present study i t was shown that the s t r i d u l a t i o n of Cenocorixa males c o r r e l a t e s w i t h sex-u a l m a turity. Thus, males of Corixidae w i l l s t r i d u l a t e out-side of the breeding season. In some other i n s e c t s s t r i d u l a t i o n has been reported s e v e r a l months before a c t u a l mating. For instance Van Tassel (1965) r e p o r t s beetles of the genus Berosus (Hydrophilidae) to s t r i d u l a t e when brought i n t o the l a b o r a t o r y i n January. The presence of mature sperm was not i n v e s t i g a t e d i n that study, but because the author reports the males to have attempted c o p u l a t i o n at the time that they s t r i d u l a t e d , they probably were s e x u a l l y mature. Females, however, obviously reached sexual m a t u r i t y s e v e r a l months l a t e r because success-f u l c o p u l a t i o n s were not observed u n t i l May. The f a c t t h a t s t r i d u l a t i o n i n Cenocorixa males i s co r r e -l a t e d w i t h sexual maturity, was a l s o shown w i t h specimens taken i n t o the l a b o r a t o r y i n l a t e f a l l . Such males s t r i d -u l a t e d and made attempts at c o p u l a t i o n , but females always r e j e c t e d the males at t h i s time. Two to three weeks l a t e r some of the females reached sexual m a t u r i t y , apparently because the room temperature was high enough to al l o w t h i s , and the food supply ( f r o z e n b r i n e shrimps) was s u f f i c i e n t . At t h i s time the males were accepted and copulations were s u c c e s s f u l . The f a c t that no copulations occur normally In 168 l a t e f a l l i n the n a t u r a l environments was demonstrated by t a k i n g female i n s e c t s from the f i e l d and keeping them at room temperature without males: some of the females matured i n about three weeks and l a i d eggs, but no l a r v a e hatched from these eggs and no embryonic development was detected. The females seem not to have mated and thus they do not store sperm over winter i n the receptaculum seminis. S t o r i n g sperm over winter i n the receptaculum seminis i s a common phenom-enon i n temperate s o c i a l Hymenoptera (Richards, 1961) . The question of how sexual m a t u r i t y i n Cenocorixa males induces these bugs to s t r i d u l a t e was not i n v e s t i g a t e d i n the present study. However, there have been attempts to study t h i s p r e v i o u s l y i n other i n s e c t s . H a s k e l l ( i 9 6 0 ) , f o r in s t a n c e , r e p o r t s that c a s t r a t e d males of grasshoppers (Orthoptera, Truxalinae) s t r i d u l a t e , perform c o u r t s h i p d i s p l a y , and cop-u l a t e . According to t h i s , a c t u a l presence of sperm is. not necessary i n these grasshoppers. The annual rhythm of s t r i d u l a t i o n i n Cenocorixa females could not be studied i n the f i e l d . However, b e h a v i o r a l exper-iments showed that only females w i t h chorionated eggs i n the l a t e r a l oviducts responded to the male s i g n a l s by answering, p r o v i d i n g t h a t they had not mated r e c e n t l y . Thus, the s t r i d -u l a t i o n of females c o r r e l a t e s both with sexual m a t u r i t y and a "need" f o r a mate. The question of what changes the behavior of a recep-t i v e female to an unreceptive one was not studied i n d e t a i l i n the present work. However, i t was n o t i c e d that the recep-t i v e females always had chorionated eggs i n the l a t e r a l o v i -169 ducts, and no embryonic development occurred i n the eggs l a i d by these females. Mating changed the females from r e c e p t i v e to unreceptive, and eggs l a i d by these females developed normally and l a r v a e hatched. I t was a l s o observed that i n t e r r u p t e d c opulations (allowed to l a s t only 1-2 seconds) were enough to make the females unreceptive. Whether or not sperm was t r a n s f e r r e d i n these copulations was not studied. The stimulus f o r females to be unreceptive could thus be chemical, t a c t i l e , or both. I t has been shown that the females of c e r t a i n grass-hoppers ( H a s k e l l , i 9 6 0 ) and katydids (Spooner, 1964) seem to be r e c e p t i v e to males i n a. way s i m i l a r to Cenocorixa f e -males: a mated female i s not r e c e p t i v e u n t i l a f t e r s e v e r a l o v i p o s i t i o n s . H a s k e l l ( i 9 6 0 ) claims t h a t the presence of sperm i n the receptaculum seminis has a chemical e f f e c t upon the female. However, i t should be noted t h a t sperm or accessory gland m a t e r i a l or both do not always have to be l o c a t e d i n the receptaculum seminis to be c h e m i c a l l y e f f e c t i v e . Davey (1958) has shown th a t the spermatophore i n Rhodnius (Hemiptera, Heteroptera, Reduviidae) induces rhythmic c o n t r -a c t i o n s of the bursa c o p u l a t r i x , and i n Drosophila the w a l l s of the vagina secrete f l u i d of an insemination r e a c t i o n ( P atterson, 1946; Lee, 1950) soon a f t e r c o i t u s and t h i s may s t a r t before c o p u l a t i o n i s completed ( P a t t e r s o n and Stone, 1952). Insect g e n i t a l i a have sense organs which are important i n mating (Scudder, 1971) and the f u n c t i o n of these could be s u f f i c i e n t to terminate the response of the female. Spooner (1964) claims that i n katydids the presence of eggs i n the 170 ovaries determines the p o s i t i v e response of females: as soon as the eggs move to the l a t e r a l oviducts the response i s i n h i b i t e d . In c o n t r a s t , i n Cenocorixa the presence of eggs i n the l a t e r a l oviducts seems to be e s s e n t i a l f o r r e c e p t i v e -ness. :.,: 171 3. S t r i d u l a t o r y behavior Observations on the s t r i d u l a t o r y behavior of Cenocorixa males i n d i c a t e t h a t s t r i d u l a t i o n commences spontaneously, p r o v i d i n g the males are s e x u a l l y mature. In general c l a s s -i f i c a t i o n s of the f u n c t i o n of i n s e c t s i g n a l s (Dumortier, 1963 c; Alexander, 1967; 1968) t h i s would be c l a s s i f i e d as a c a l l i n g s i g n a l , and i t s f u n c t i o n would be to f a c i l i t a t e p a i r - f o r m a t i o n by a t t r a c t i n g c o n s p e c i f i c females. The exp-eriments confirmed t h a t t h i s i s the case i n Cenocorixa. How-ever, experiments a l s o showed that s i g n a l s of males would o f t e n s t i m u l a t e other males to s t r i d u l a t e . D i f f e r e n c e s were detected between the species i n t h e i r readiness to answer va r i o u s s i g n a l s . When c o n s p e c i f i c male s i g n a l s were used ( F i g . 52, Table V I I I ) , some, but not a l l Cenocorixa species r e a d i l y answered these s i g n a l s . Further, i n cases when c e r t a i n species are able to produce two d i f f e r e n t c a l l s ( f i r s t p a r t of the c a l l alone or complete s i g n a l ) , the males answered the slow pu l s a t e d f i r s t p a r t more r e a d i l y than a complete s i g n a l (e.g. C_. andersoni: Table V I I I ) . Both spontaneous and sound evoked s t r i d u l a t i o n has been observed i n male Corixidae p r e v i o u s l y ( S c h a l l e r , 1951; Leston, 1955; Leston and P r i n g l e , 1963; Finke, 1968), and the s i g n a l s have been c l a s s i f i e d mostly as c a l l i n g s i g n a l s . Further, a very commonly held concept i s that a c o u r t s h i p s i g n a l as d i s t i n c t from a c a l l i n g s i g n a l a l s o e x i s t s : M i t i s (1936) observed i n Sigara s t r i a t a , t h a t a male observing a female, s t a r t e d s t r i d u l a t i n g very a c t i v e l y w i t h shortened i n t e r v a l s and longer s i g n a l s . A l s o Leston (1955), Southwood and Leston 172 (1959), and Leston and P r i n g l e (1963) c l a i m that a c o u r t -ship s i g n a l has been observed i n c o r i x i d s , but they do not e x p l a i n the d i f f e r e n c e between the s i g n a l s belonging to the c a l l i n g or c o u r t s h i p c a t e g o r i e s . H a s k e l l (1961) st a t e s that male;-, c o r i x i d s - can g e n e r a l l y produce two s i g n a l s , and i t i s suggested t h a t one i s a c a l l i n g s i g n a l , the other a c o u r t -ship s i g n a l , although t h i s has yet to be confirmed. In the present study i t was f r e q u e n t l y observed that as w e l l as s t r i d u l a t o r y s i g n a l s , a v i s u a l stimulus from a male, female, or specimen of another species induced Cenocorixa males to s t r i d u l a t e . No d i f f e r e n c e was detected i n the s t r u c t u r e of these response s i g n a l s except .in cases when the response, s i g n a l was only a p a r t of the normal c a l l or c a l l i n g s i g n a l , which of t e n , but not always happened i n (J. andersoni, (J. utahensis, and CJ. b l a i s d e l l i . According to the d e f i n i t i o n of a c o u r t s h i p s i g n a l [Dumortier (1963 c ) : a d i s p l a y of the male, set o f f by a stimulus from the female], 'this induced s i g n a l i s not a c o u r t s h i p s i g n a l . Leston and P r i n g l e (1963) s t a t e that the c a l l i n g s i g n a l of c o r i x i d s may i n c l u d e r i v a l r y or t e r r i t o r i a l f u n c t i o n . Further, when movements of C_. b i f i d a males were compared i n the s i t u a t i o n s where the males were alone or exposed to a s t r i d u l a t o r y stimulus, i t was shown that s i g n i f i c a n t l y more swimming ( e s p e c i a l l y short range swimming) occurred when s t r i d u l a t o r y s i g n a l s were present. In observations on males of (J_. b i f i d a and (J. b l a i s d e l l i i t was found that s t r i d u l a t i o n was o f t e n followed by nudging and chasing behavior which serves to space out i n d i v i d u a l s . This suggests that the s t r i d -173 u l a t i o n i n Cenocorixa f u n c t i o n s as an a g o n i s t i c s i g n a l . S i m i l a r l y , Leston and P r i n g l e (1963) re p o r t that Sigara  d o r s a l i s (Leach.) males, s t r i d u l a t i n g a l t e r n a t e l y , move towards each other u n t i l t h e i r heads come together, and one of them f i n a l l y nudges the other one away. In £. b i f i d a and C_. b l a i s d e l l i , i f the specimens were w i t h i n v i s u a l range of each other, they d i d not move towards each other during the s i g n a l l i n g which preceded the nudging. In Cenocorixa, the s i g n a l s produced i n a g o n i s t i c s i t u -a t i o n s , d i d not u s u a l l y d i f f e r s t r u c t u r a l l y from spontaneously produced c a l l i n g s i g n a l s , although t h e i r f u n c t i o n apparently i s d i f f e r e n t . In c o n t r a s t , Orthopterans have a more h i g h l y developed a c o u s t i c communicating system o f t e n w i t h s t r u c t -u r a l l y d i f f e r e n t s i g n a l s f o r d i f f e r e n t purposes (Dumortier, 1963 c ) . However, the f u n c t i o n of the a g o n i s t i c s i g n a l s of Cenocorixa males seems to be the same as the f u n c t i o n of a r i v a l ' s song i n Dumortier's (1963 c) c l a s s i f i c a t i o n : an emis-s i o n produced, u s u a l l y a l t e r n a t e l y , by two i n d i v i d u a l s a short distance from each other, denoting the s o - c a l l e d r i v a l r y or t e r r i t o r i a l behavior. In _C. b i f i d a , when a s t r i d u l a t i n g male was within^a-.:few centimetres of an unreceptive female, apparently approaching the l a t t e r , the female was observed to swim away from the c a l l i n g male (escape) or d i s t u r b the male by swimming towards i t ( a g o n i s t i c behavior). A r e c e p t i v e female, on the other hand, w i t h i n the range of the sound of the c a l l i n g male, would stay motionless and s t r i d u l a t e i n answer to the male c a l l . In other words, a r e c e p t i v e female produced an agreement 1 7 4 s i g n a l [according to c l a s s i f i c a t i o n of Dumortier ( 1 9 6 3 c ) ] . Males were observed to o r i e n t a t e d i r e c t l y to the female according to t h i s agreement s i g n a l . No true c o u r t s h i p d i s p l a y was observed i n any species of Cenocorixa. In the mating experiments c a r r i e d out i n the c u l t u r e t r a y s , i t was found t h a t the males could not o r i e n t to and l o c a t e the females on t h e i r agreement song owing to echoes from the w a l l s of the t r a y s . In these cases the males swam very f a s t i n small c i r c l e s and produced s i g n a l s which were d i f f e r e n t from "normal" c a l l i n g s i g n a l s : the pulse r a t e i n these s i g n a l s was more i r r e g u l a r than i n the c a l l i n g s i g n a l s , and the d u r a t i o n of the s i g n a l s was short, but the s i g n a l s were repeated more f r e q u e n t l y than normally. In s e v e r a l species these s i g n a l s were produced while the males were swimming (normally s i g n a l s are only produced while the specimens are r e s t i n g on the bottom). However, i t was observed th a t the females d i d not answer these unusual c a l l s . The next female s i g n a l occurred only a f t e r the male produced a "normal" s i g n a l again. Thus these unusual male s i g n a l s are not c o u r t -ship s i g n a l s , but s i g n a l s created by an unnatural s i t u a t i o n . Males of C_. andersoni and C. /.utahensis can produce e i t h e r a complete s i g n a l or the f i r s t part of the s i g n a l alone. I t was found that males o f t e n respond to the f i r s t p a r t of the s i g n a l more r e a d i l y than to the complete s i g n a l , w h i l e r e c e p t i v e females w i l l respond to only the complete s i g n a l s and not p a r t s of them (Tables V I I I and X). This suggests that the complete s i g n a l , which i s the c a l l i n g song, i s used to a t t r a c t females, while the incomplete s i g n a l seems 175 to hav.e the f u n c t i o n of an a g o n i s t i c s i g n a l . On the other hand, C_. b l a i d e l l i and C_, wileyae males produce the two p a r t s of the s i g n a l s o f t e n independently from each other, and both females and males seem to respond only to a complete s i g n a l or only to the l a s t p a r t of the s i g n a l : the d i f f -e r e n t i a t i o n of the f u n c t i o n s of the s i g n a l s does not seem to be c l e a r i n these two species. In the European Sigara  d o r s a l i s , H a s k e l l (1961) suggests that one s i g n a l could be a c a l l i n g song, the other a c o u r t s h i p song, but according to the observations i n Cenocorixa they f u n c t i o n as a c a l l i n g song.and an a g o n i s t i c song. However, working on Sigara  s t r i a t a , which has s i g n a l s almost s i m i l a r to the s i g n a l s of S_. d o r s a l i s , Finke (1968) could not detect any d i f f e r e n c e i n the f u n c t i o n s of the two c a l l s . In Cenocorixa s t i m u l i f o r a s u c c e s s f u l c o p u l a t i o n seem to be i*)1 c a l l i n g s i g n a l of the male, and i i ) agreement s i g n a l of the female. In o r i e n t i n g to the r e c e p t i v e female from a great d i s t a n c e , males of a l l species depend on a u d i t -ory s t i m u l i , but at c l o s e range v i s u a l s t i m u l i seem to be important i n most species. However, C_. dakotensis does not seem to o r i e n t to v i s u a l s t i m u l i at a l l , but only to a u d i t -ory s t i m u l i . This i s understandable since _C. dakotensis i s the only species which was never observed to s t r i d u l a t e spontaneously during daytime. S c h a l l e r (1951) claims that the response of females of Sigara s t r i a t a to a male song i s to swim r a p i d l y i n small c i r c l e s , and thus, since the male w i l l t r y to copulate w i t h any moving object of s u i t a b l e s i z e , mating i s i n i t i a t e d , i . e . 1 7 6 the movement of the female a t t r a c t s the male. However, Finke ( 1 9 6 8 ) , a l s o worked on S_. s t r i a t a , observed no increase i n short range swimming of females i n response to male c a l l s , but a d i f f e r e n c e i n long range swimming of the females was observed ("Aufschwimmen, langere Bewegungen im Aquarium"): the swimming a c t i v i t y of females increased when the male s i g n a l s were payed. I t seems to me that i n both cases ( S h a l -l e r , 1 9 5 1 ; Finke, 1 9 6 8 ) the r e a c t i o n of the females of £. s t r i a t a was not a premating response, but an escape r e a c t i o n of unreceptive females. During the present study i t was f r e q u e n t l y observed t h a t not only females, but a l s o males of Cenocorixa would swim i n small c i r c l e s i n c u l t u r e t r a y s when stimulated by male s i g n a l s from specimens c l o s e b y ( o r i e n t a t i o n was im-p o s s i b l e owing to echoes). This o f t e n a t t r a c t e d other C o r i x -idae and l e d to c o p u l a t i o n attempts between two males or males and females of d i f f e r e n t species or even d i f f e r e n t genera! However, even when the male and female were of the same species, the attempt at co p u l a t i o n , without the preced-i n g agreement s i g n a l of the female, was unsuccessful. I t i s r e c a l l e d that i n Cenocorixa the r e a c t i o n of un-re c e p t i v e females placed w i t h caged s t r i d u l a t i n g males was for" the""..females to remain motionless, the males not being able to get i n t o c l o s e p r o x i m i t y to the females. On the other hand, unreceptive females placed so that the s t r i d u l a t i n g males could come i n t o contact w i t h them, d i d not stay s t i l l , but escaped. S c h a l l e r ' s ( 1 9 5 1 ) experiments were c a r r i e d out i n g l a s s aquaria and i n these I have n o t i c e d p l e n t y of echoes, 177 as Indeed S c h a l l e r (1951) a l s o reported. Females under such c o n d i t i o n s would not be able to o r i e n t a t e away from the male because the sound would appear to come from everywhere. In F i n k e 1 s (1968) study the females of S_. s t r i a t a used were c o l l e c t e d i n e a r l y s p r i n g , and then kept i n constant tem-perature cabinet a t 4°C u n t i l e a r l y May when the experiments were c a r r i e d out. While t h i s i s the time that mating occurs i n the n a t u r a l h a b i t a t , experiments w i t h Cenocorixa demonstrated th a t females kept at 4°C would not a t t a i n sexual maturity. Thus the female specimens used by Finke (1968) were probably s e x u a l l y immature, and the swimming observed, was probably an escape r e a c t i o n . A morphological study of females of s e v e r a l European species ( c o l l e c t i o n s of Dr. G. G. E. Scudder: Corixa dentipes, Sigara d o r s a l i s , A r c t o c o r i s a germari, C a l l i c o r i x a praeusta) showed that a plectrum and pars s t r i d e n s e x i s t s s i n b t h e s e . In previous studies ( M i t i s , 1936; S c h a l l e r , 1951; Finke, 1968) females are reported to l a c k the s t r i d u l a t o r y apparatus. I t i s true t h a t t h i s apparatus-in the females of the European species st u d i e d i s l e s s developed than the apparatus of the males, and f o r instance the _S. d o r s a l i s male has about 12 rows of w e l l developed pegs i n the pars s t r i d e n s , while the female only has about seven rows of these pegs and they are not as s t r o n g l y thickened as i n the male. A s i m i l a r tendency to have l e s s developed s t r i d u l a t o r y apparatus was found i n Cenocorixa females when compared t o t t h e males \ ( c f . Table I , F i g . 4). However, there i s no doubt that the females of the European species studied are able to s t r i d u l a t e . This i s al s o 1 7 8 supported by Southwood and Leston ( 1 9 5 9 ) who s t a t e that both sexes of A r c t o c o r l s a germari s t r i d u l a t e during the breeding season, although nothing i s s a i d about how t h i s i s connected w i t h breeding. Further, during the present study, s t r i d u l a t o r y s i g n a l s of both sexes of Sigara nevadensis Walley were r e c -orded ( c f . Appendix I I ) , and t h e i r f u n c t i o n was observed to be the same as the f u n c t i o n of the s i g n a l s i n Cenocorixa. C r i s p ( 1 9 6 2 ) has described the mating i n A r c t o c o r i s a  germari and notes that the male detects the female when the l a t t e r i s swimming by. The male then chases the female and mounts the female while the p a i r i s swimming, and then the p a i r comes up tov.the surface where c o p u l a t i o n occurs. Thus the occurrence of copulations i n the n a t u r a l h a b i t a t s i s e a s i l y observed ( C r i s p , 1 9 6 2 ) . In Cenocorixa, a s i m i l a r sequence of events was f r e q u e n t l y observed, but i n t h i s genus i t only occurred between an a c t i v e male and an un-r e c p t i v e female: the p a i r came to the surface because of the re l e a s e behavior of the female. In a s u c c e s s f u l c o p u l a t i o n i n Cenocorixa the p a i r never comes up to the surface during the i n i t i a t i o n of c o p u l a t i o n , but i f the c o p u l a t i o n l a s t s a long time, the p a i r may o c c a s i o n a l l y come to the surface to renew i t s a i r supply. In a few previous stud i e s on European c o r i x i d s i t had been noted that the song of males does not seem to have any v i s i b l e e f f e c t upon the females ( M i t i s , 1 9 3 6 ; Larsen, 1 9 3 8 ; Jansson, 1 9 6 8 ) . However, i n a l l of these studies both sexes apparently were kept a l l the time i n the same container, and thus, i f the species are l i k e Cenocorixa species, most females 179 i n such c u l t u r e s would be mated immediately when they become r e c e p t i v e , and most of the time the females would be unrecept-i v e . In the experiments c a r r i e d out w i t h C_. b i f i d a , an i n t e r -e s t i n g d i f f e r e n c e between d i f f e r e n t males was obtained i n the' presence of female odor: the male kept i s o l a t e d from a l l other specimens r e a d i l y s t r i d u l a t e d i n the presence of female odor, but the males picked up randomly from a mixed male-fe-male c u l t u r e d i d not show any increased s t r i d u l a t i n g a c t i v i t y . The males from the mixed c u l t u r e d i d not r e a c t to the odor of females, perhaps because the experimental s i t u a t i o n d i d not d i f f e r i n t h i s regard from the c o n d i t i o n s i n t h e i r c u l t u r e t r a y . However, f o r the male kept i s o l a t e d from a l l other specimens, the female odor c l e a r l y was a stimulus to s t r i d -u l a t i o n (male odor d i d not have any e f f e c t ) . In t h i s e x p e r i -ment only one specimen was t e s t e d , but because s i m i l a r observ-a t i o n s on the e f f e c t of female odor have been made on Sigara  omani (Hungfd.) (Jansson, unpublished), the r e s u l t s are con-sidered r e l i a b l e . The only reference:, t.o pheromones i n Corixidae i s i n the study of Pinder and Staddon (1965 a; 1965 b ) , which shows tha t trans - 4-oxohex - 2-enal i s secreted from the metathoracic glands of both Sigara f a l l e n ! (Fieb.) and C o r i x a dentipes (Thorns.). The metathoracic s t i n k glands, as w e l l as the l a r v a l d o r s a l abdominal glands have been studied anatomically and h i s t o l o g i c a l l y i n v a r i o u s Corixidae ( B r i n d l e y , 1929; Betten, 1943), and the f u n c t i o n of the s e c r e t i o n , l i k e that i n land bugs (Remold, 1962), has been suggested to be p r o t e c t i v e . 180 The f a c t that the s e c r e t i o n i s not species or sex s p e c i f i c supports t h i s concept (Pinder and Staddon, 1965 a). However, Benwitz (1956) has described a d d i t i o n a l glands, l o c a t e d i n a l l three p a i r s of legs of Corixidae^ the s e c r e t i o n and f u n c t i o n of which are unknown. I t i s p o s s i b l e that some other pheromone occurs i n Corixidae and acts as a sexual a t t r a c t a n t . A l t e r n a t i v e l y , the defensive s e c r e t i o h i may under c e r t a i n circumstances have a s u b s i d i a r y f u n c t i o n , namely th a t of sexual a t t r a c t i o n . How-ever, i n Cenocorixa the method using a c o u s t i c s t i m u l i i s very e f f e c t i v e and the importance of pheromones has not been e l u c i d a t e d . On the other hand, s e v e r a l n o n - s t r i d u l a t i n g species of Corixidae e x i s t , and the mating behavior of these species i s completely unknown. In these the r o l e of s t r i d -u l a t i o n might be replaced by pheromones. Butenandt (1955) has i d e n t i f i e d trans-hex-2-enyl-acetate i n Lethocerus i n d i c u s ( L e p e l e t i e r and S e r v i l l e ) , another water bug (Belostomatidae), and because t h i s chemical i s sex s p e c i f i c , o c c u r r i n g i n males only, i t i s suggested to f u n c t i o n as a sex a t t r a c t a n t . 181 4. E v o l u t i o n a r y s i g n i f i c a n c e of s t r i d u l a t i o n i n the genus Cenocorixa Sound production i n i n s e c t s i s advantageous i f the sounds are produced i n connection w i t h sexual behavior and can guide p a i r - f o r m a t i o n ( H a s k e l l , 1961). A c o u s t i c communi-c a t i o n i n Orthoptera and i t s s i g n i f i c a n c e i n p a i r - f o r m a t i o n has been discussed a number of times ( c f . Alexander, 19^7; 1968). However, only i n a few cases has i t been shown ex-p e r i m e n t a l l y that the s i g n a l s a c t u a l l y f u n c t i o n as a pre-mating i s o l a t i n g mechanism so t h a t the females are a t t r a c t e d by s i g n a l s of c o n s p e c i f i c males, but do not respond to male s i g n a l s of other species (Walker, 1957; Perdeck, 1958; Has-k e l l , 1958; 1961). The behavioral experiments c a r r i e d out during the present study showed that both males and females of Cenocorixa are u s u a l l y able to d i s c r i m i n a t e the s i g n a l s of the opposite sex of c o n s p e c i f i c specimens from the s i g n a l s of a l l other species. By comparing the s i g n a l s of v a r i o u s species i t i s obvious t h a t the frequency of the sound cannot have any r o l e i n the species/sex r e c o g n i t i o n . This has a l s o been observed i n v a r i o u s other i n s e c t s ( c f . H a s k e l l , 1961). Walker (1957) suggests that the key character i n species r e c o g n i t i o n of t r e e c r i c k e t s (Orthoptera, G r y l l i d a e , Oecanthinae) i s the pulse r a t e . However, H a s k e l l (1961) does nof agree w i t h t h i s because i n d i v i d u a l v a r i a t i o n i n the pulse r a t e Is q u i t e l a r g e , and the pulse rates of v a r i o u s species o f t e n overlap. H a s k e l l (1961) claims that the key. character i s pulse modulation (= temporal p a t t e r n of pulses i n a s i g n a l ) , t h i s 182 being very constant and species s p e c i f i c character i n Orth-opteran s i g n a l s . Bennet-Clark and Ewing (1969), on the other hand, c l a i m that pulse i n t e r v a l i s the c r i t i c a l parameter i n the c o u r t s h i p song of Drosophila melanogaster, but because the s i g n a l s of t h i s f l y are composed of pulses, each of which i n -clude only one impact, the pulse i n t e r v a l could r e f e r to pulse r a t e as w e l l as to the temporal p a t t e r n of pulses. In Cenocorixa, owing to i n t r a s p e c i f i c v a r i a t i o n , the pulse rates of v a r i o u s species ( F i g s . 17-26) seem to over-la p much more than those of t r e e c r i c k e t s (Walker, 1957), although the r e g r e s s i o n l i n e s of the species are more or l e s s d i f f e r e n t . However, the temporal p a t t e r n of pulses i n Cenocorixa i s always constant and species s p e c i f i c , thus supporting H a s k e l l ' s (1961) concept t h i s being the key char-a c t e r . On the other hand, the loudness of the s i g n a l s vary g r e a t l y between the species (according to s u b j e c t i v e observ-a t i o n s ) , and the s t r u c t u r e of pulses (arrangement of impacts i n a pulse) and the number of impacts per pulse are u s u a l l y more or l e s s s p e c i f i c ; these f a c t o r s might a l s o have an im-portant r o l e i n species d i s c r i m i n a t i o n . A thorough study i n -v o l v i n g e l e c t r o p h y s i o l o g i c a l recordings i s r e q u i r e d , but was outside the aims of the present t h e s i s . The Corixidae have a u d i t o r y organs i n the thorax (Hagemann, 1910; S c h a l l e r , 1951), but i t i s not known what d i f f i c u l t i e s would a r i s e i f recording w i t h electrodes connected to the nerves i s t r i e d . H a s k e l l (1961) has discussed whether the s t r i d u l a t i o n alone i s important i n species r e c o g n i t i o n i n grasshoppers, or i f i t works together w i t h some other f a c t o r or f a c t o r s . 183 Experiments w i t h Orthoptera have demonstrated that o f t e n v i s u a l and chemical s t i m u l i may accompany s t r i d u l a t i o n and p l a y important r o l e s i n the mating behavior. In the present study i t was a l s o observed that v i s u a l stimulus apparently i s important i n most species i n c l o s e range approach, but species d i s c r i m i n a t i o n seems to be s o l e l y on the b a s i s of the a u d i t o r y stimulus. In a d d i t i o n to the c h a r a c t e r i s t i c d i f f e r e n c e s i n the s t r u c t u r e of the s t r i d u l a t o r y s i g n a l s , temporal d i f f e r e n c e s i n the s t r i d u l a t i n g a c t i v i t y of the species were a l s o observed. This again i s s i m i l a r to Orthopterans, w i t h some species s t r i d -u l a t i n g i n day time, others at night time (Dumortier, 1963 c ) . F i g . 61 summarises the d i e l p e r i o d i c i t y of the s t r i d u l a t i n g a c t i v i t y of a l l Cenocorixa species as i n d i c a t e d both by l a b o r a t o r y experiments and f i e l d observations. There i s e v i d e n t l y a p a r t i a l temporal i s o l a t i o n i n the s t r i d u l a t i n g a c t i v i t y , and i n one p a i r of sympatric species (C.. b i f i d a -C_. expleta) t h i s d i f f e r e n c e was a l s o observed i n the n a t u r a l h a b i t a t s . Cenocorixa does not r e l y completely, however, on the s t r i d u l a t i o n behavior f o r species i s o l a t i o n , although t h i s would appear to c o n s t i t u t e the main i s o l a t i n g mechanism i n sympatric s i t u a t i o n s . I t i s r e i n f o r c e d by d i f f e r e n c e s i n geographic d i s t r i b u t i o n and h a b i t a t preference. The study of the geographic d i s t r i b u t i o n of the species i n d i c a t e s some geographic i s o l a t i o n ( F i g s . 54-57), but owing to the d i f f -i c u l t i e s i n i d e n t i f i c a t i o n of Cenocorixa species ( c f . App-endix I ) , the published records c e r t a i n l y i n c l u d e some mis-184 a F i g . 6 1 . Summary of the d i e l p e r i o d i c i t y of the s t r i d -u l a t i n g a c t i v i t y of Cenocorixa males. Explanations: a b s c i s s a = time of day; s t i p p l e d area expresses the r e l a t i v e a c t i v i t y i n s t r i d u l a t i o n . A = C_. b i f i d a ; B = _C. k u i t e r t i ; C = C_. andersoni; D = _C. utahensis; E = C_. dakotensis; F = _C. b l a i s d e l l i ; G = C_. wileyae; H = C_. e x p l e t a . 184 b 24 6 12 18 24 185 i d e n t i f i c a t i o n s , and some minor m o d i f i c a t i o n s to the recorded d i s t r i b u t i o n s and range can be expected i n the f u t u r e . In cases when two or more Cenocorixa species are observed s y m p a t r i c a l l y , e c o l o g i c a l d i f f e r e n c e s are u s u a l l y observed. Scudder (1969 a; 1969 b) has reported a p a r t i a l e c o l o g i c a l i s o l a t i o n between C_. b i f i d a and C_. expleta, since they i n h a b i t d i f f e r e n t ranges of s a l i n i t y . This i n f o r m a t i o n was confirmed during the present study, but another p a r t i a l e c o l o g i c a l i s o -l a t i o n between the two species was detected i n cases when s a l i n i t y allows the two to occur i n same l a k e : C_. b i f i d a i n h a b i t s the very edges of the lakes i n s i d e reed beds, wh i l e <C. expleta. p r e f e r s s l i g h t l y deeper water outside reed beds. P a r t i a l e c o l o g i c a l i s o l a t i o n s were a l s o detected between other Cenocorixa p a i r s : C_. andersoni i n permanent ponds, _C. b l a i s d e l l i i n temporary pools; _C. k u i t e r t i i n slo w l y running or o l i g o t r o p h i c waters, C_. wileyae i n stagnant, more eutrophic waters. In Table X I I I I have c o l l e c t e d together estimates on the e f f e c t i v e n e s s of va r i o u s i s o l a t i n g mechanisms between the species of Cenocorixa i n the l i g h t of the present study. The form of the t a b l e i s s i m i l a r to t h a t of Moore (19^9) f o r i s o -l a t i o n of a group of frogs i n the northeast of North America. However, geographic i s o l a t i o n i n my t a b l e i s only very roughly estimated because the d e t a i l e d d i s t r i b u t i o n s of the species are unknown. E c o l o g i c a l i s o l a t i o n i s according to my observations or i s the p o t e n t i a l l y expected value. Seasonal i s o l a t i o n does not e x i s t between Cenocorixa species, and i s always 0. Temporal i s o l a t i o n i n d i e l p e r i o d i c i t y of the s t r i d -186 u l a t i n g a c t i v i t y i s estimated from l a b o r a t o r y experiments and a c t u a l observations i n n a t u r a l environments; s t r i d -u l a t o r y i s o l a t i o n i s taken d i r e c t l y from playback experiments (Table X). From the Table X I I I i t can be seen t h a t the two strong-est i s o l a t i n g mechanisms are geographic i s o l a t i o n and s t r i d -u l a t o r y i s o l a t i o n . In s e v e r a l cases they are both 100 per cent e f f e c t i v e , but i t should be noted that e s p e c i a l l y when geographic i s o l a t i o n i s not complete, the s t r i d u l a t o r y one i s . On the ojher hand the only case when s t r i d u l a t o r y i s o -l a t i o n seems to f a i l a l t o g e t h e r , happens i n _C, wileyae f e -males which answer C_. dakotensis male c a l l s every time. How-ever, C_. dakotensis males do not answer the s i g n a l s of C_. wileyae females very a c t i v e l y (Table I X ) , and no searching behavior was observed i n C_. dakotensis males when stimulated w i t h C_. wileyae female s i g n a l s . In a d d i t i o n , these two species have a f i r m geographic i s o l a t i o n : C_. dakotensis occupies the northern p l a i n s east of the Rocky Mountains whi l e _C. wileyae has i t s d i s t r i b u t i o n mostly between the Rocky Mountains and the Coast Range. Table XIII. Estimates of the magnitude of d i f f e r e n t i s o l a t i n g mechanisms i n Cenocorixa. G = geographic V i s o l a t i o n ; E = eco l o g i c a l i s o l a t i o n ; S = s t r i d u l a t o r y i s o l a t i o n ; T = temporal i s o l a t i o n i n s t r i d u l a t i o n . ^ M a l e s F ema.l e s b i f i d a kuit b i f i d a G 100 E 50 S 90 T 8o k u i t e r t i G 100 E 0 S _ T 80 andersoni G 100 100 E 0 0 S 100 -T 80 0 utahensis G 50 . 95 E 0 0 S 100 -T 60 0 dakotensis G 20 100 E 0 0 S 100 100 T 90 0 b l a i s d e l l i G 100 100 E 0 0 S 100 -T 50 0 wileyae G 90 95 E 0 50 S 100 90 T 70 30 expleta G 0 100 E x 30 100 S 100 100 T 50 0 andersoni utahensis dakotensis b l a i s d e l l i wileyae expleta 100 50 60 ; 80 100 0 0 100 0 100 10 100 0 100 10 60 75 100 0 100 0 100 30 100 100 100 0 10 50 8o 60 0 0 0 100 0 100 0^ 40 0 100 10 100 0 100 0 10 0 90 0 10 90 100 0 40 50 100 90 100 0 10 100 0 100 10 60 0 100 30 100 0 80 30 100 0 0 50 30 90 8o 30 100 . 90 30 50 0 30 100 100 100 40 50 60 100 0 100 0 0 100 0 40 10 50 100 100 75 0 • 100 100 - 100 ~ 0 50 10 100 50 60 0 0 90 100 ' - 100 10 40 0 100 100 60 0 0 90 100 100 100 0 50 0 100 100 0 100 _ 8o 20 0 100 95 0 70 100 60 40 - 20 100 95 100 70 I 90 100 20 188 5. E v o l u t i o n and s t r i d u l a t i o n i n Corixidae In general i n e v o l u t i o n i t i s the more complicated forms tha t are the most advanced ones (Rensch, 1959)• I f t h i s concept i s a p p l i e d to the s t r u c t u r e of the s t r i d u l a t o r y s i g n a l s of Cenocorixa males, an order can be obtained as shown i n F i g . 62. C e r t a i n l y the genus can be d i v i d e d i n t o two subgroups according to the s t r u c t u r e of male s i g n a l s : 1) Signals composed of an uninterrupted sequence of pulses; the b i f i d a group (£. b i f i d a , _C.. k u i t e r t i , C. andersoni, C_. utahensis, and C.. dakotensis) and 2) S i g n a l s composed of d i s t i n c t l y separate groups of pulses; the wileyae group (C!. b l a i s d e l l i , _C. wileyae, and _C. e x p l e t a ) . This sub-d i v i s i o n of the genus c o i n c i d e s w i t h a d i v i s i o n that e x i s t s i n morphological c h a r a c t e r s . The wileyae group i n body form i s more slender than the b i f i d a group, and the r i g h t paramere of the male g e n i t a l i a i n the l a t t e r group i s b i f u r c a t e (except i n _C. andersoni), while i n the wileyae group i t i s not b i -f u r c a t e . In _C. andersoni the non-bifurcate form of the para-mere might be a secondary m o d i f i c a t i o n . The general geographic d i s t r i b u t i o n of the genus suggests a western o r i g i n i n areas south of the P l e i s t o c e n e g l a c i a t i o n . However, the e v o l u t i o n could have been pre or post P l e i s t o c e n e or p a r t l y both. I f more d e t a i l e d s p e c u l a t i o n of e v o l u t i o n of the genus i s d e s i r e d , my suggestion, based on zoogeography, morphology, and s t r i d u l a t i o n d i f f e r e n c e s , would be as f o l l o w s : The ancestors of the genus were something l i k e present day C_. b i f i d a . At some time t h i s a n c e s t r a l form was s p l i t 189 a b t i l l 1111 m i l 1111 i l l l l l OOUlGMIIMi! s h F i g . 62. Diagram of suggested i n c r e a s i n g complexity .of s i g n a l s of Cenocorixa males. The s i m p l i e s t type i s at the top. a = _C. b i f i d a ; b = _C. k u i t e r t i ; c = C, andersoni; d - _C. utahensis; e = C_. dakotensis; f = _C. b l a i s d e l l i ; g = _C. wileyae; h = _C. e x p l e t a . Explanations: i n each s i g n a l one bar represents one pulse; width of the bar i n d i c a t e s r e l a t i v e d u r a t i o n of the p u l s e , height of the bar r e l a t i v e loudness of the pulse. Pulse arrangement shows the temporal p a t t e r n of the s i g n a l s . In some species f i r s t p a r t of the s i g n a l can be produced alone and i n these two separate s i g n a l s are i n d i c a t e d (b, c, and d). 199 i n t o two: b i f i d a group and wileyae group. The b i f i d a group migrated i n d i f f e r e n t d i r e c t o n s : i ) Northwards i n the west-ern side of the Rocky Mountines, g i v i n g r i s e to _C. b i f i d a i n the i n t e r i o r p l a t e a u ; i i ) Northwards i n the eastern s.ide of the Rocky Mountines: _C. dakotensis; i i i ) Southwest to the high areas on mountains: C. k u i t e r t i ; i v ) Northwest to the P a c i f i c Westcoast: C_. andersoni; v) Eastwards over the Rocky Mountains: _C. utahensis. Meanwhile, the wileyae group gave r i s e to C. b l a i s d e l l i a f t e r c r o s s i n g the Coast Range to the P a c i f i c Coast i n south, and C_. e x p l e t a a f t e r migrating over the Rocky Mountains..This h y p o t h e t i c a l e v o l u t i o n i s summarised i n F i g . 63, and present day geographic d i s t r i b u t i o n can be derived from the hypothesis by a l l o w i n g £. b i f i d a to cross over the Rocky Mountains somewhere i n Wyoming - Idaho to the northern p l a i n s , and _C. utahensis and _C. e x p l e t a the other way back to the i n t e r i o r : p l a t e a u between the Rocky Mountains and the Coast Range. The f u n c t i o n of the Rocky Mountains as an i s o l a t i n g b a r r i e r i s suggested by observations on geographic v a r i a t i o n i n the s i g n a l s of C_. b i f i d a (Jansson, to be p u b l i s h e d ) : A s l i g h t d i f f e r e n c e was detected between the populations of B r i t i s h Columbia and A l b e r t a , and the p o p u l a t i o n i n northern Utah possesses an i n t e r m e d i a t e s i g n a l compared to the northern populations. A l s o some s l i g h t morphological d i f f e r e n c e s bet-ween these populations were detected ( c f . Appendix I ) . These observations do not a f f e c t the r e s u l t s of the present study, but show that the two northern populations could evolve apart i f the apparent ..connection through Wyoming - Idaho breaks. 19.1 F i g . 63 . Suggested e v o l u t i o n of Cenocorixa species. Based on geographic d i s t r i b u t i o n , general morphology, and s t r i d -u l a t i o n . 1 = C. b i f i d a ; 2 = C_. dakotensis; 3 = C_. k u i t e r t i ; 4" = _C. andersoni; 5 = C. utahensis; 6 = _C. wileyae; 7 = C.. b l a i s d e l l i ; 8 = _C. exp l e t a . • 192 Divergence i n the animal kingdom i s thought to take place by geographic i s o l a t i o n and e v o l u t i o n of e f f e c t i v e i s o l a t i n g mechanisms (Mayr, 1963). Premating i s o l a t i n g mechanisms are u s u a l l y considered the most e f f e c t i v e because they prevent waste of the sexual products. Thus, premating i s o l a t i n g mechanisms, not s u r p r i s i n g l y , are the predominant i s o l a t i n g mechanisms between c l o s e l y r e l a t e d species that occur s y m p a t r i c a l l y (e.g. B l a i r , 1955; Brown, 1965; Hagen, 1967; L i c h t , 1969; L i l e y , 1966; Spieth , 1947; Wasserman, 1957). In i n s e c t s which produce sound, a c o u s t i c s i g n a l s are suggested to be one of the commonest premating i s o -l a t i n g mechanisms (e.g. Alexander, 19^7; 1968; Alexander and Moore, 1962; Bennet-Clark and Ewing, 1969; H a s k e l l , I 9 6 I ; Perdeck, 1958; Roth and Hartman, 1967; Spooner, 1964; 1968; Van T a s s e l , 1965; Waldon, 1964; Walker, 1957). E v o l u t i o n of such sound based premating i s o l a t i n g mechanism i s an i n t e r e s t i n g problem, and Alexander (1962) suggests that i n Orthoptera, the f i r s t c r i c k e t apparently was already a s p e c i a l i z e d s t r i d u l a t o r . He f u r t h e r suggests th a t the f u n c t i o n of s t r i d u l a t i o n i n ancient c r i c k e t s was l i n k e d w i t h c o u r t s h i p behavior, and that the other f u n c t i o n s of s t r i d u l a t i o n i n l i v i n g c r i c k e t s have evolved from t h i s c o u r t s h i p song. According to Alexander (1962) t h i s concept i s supported by the f a c t t h a t c o u r t s h i p i n c r i c k e t s that have l o s t the a b i l i t y to s t r i d u l a t e , i n c l u d e s l i f t i n g of the wings. Wing l i f t i n g a s s o c i a t e d with c o u r t s h i p i s observed i n B l a t t a -r i a (Roth and W i l l i s , 1952; Roth and Hartman, 1967), and i s e v i d e n t l y a p r i m i t i v e behavior i n Orthopteroids (Alexander, 193 1964), and thus i n t h i s taxon there i s a good basis f o r the e v o l u t i o n of sound production as an a d d i t i o n to these wing l i f t i n g movements. The f u n c t i o n of the i n i t i a l c o u r t s h i p was r e s t r i c t e d to short distance a t t r a c t i o n , and i n Orthoptera, when a t t r a c t i o n from longer distances evolved, t h i s c o u r t -ship song gave r i s e to a c a l l i n g song, and when a c o u s t i c a l behavior became more complicated, other c a t e g o r i e s of songs evolved from these p r e - e x i s t i n g ones (Alexander, 1962). Various s t r i d u l a t o r y mechanisms e x i s t i n both t e r r e s -t r i a l and aquatic Hemiptera, but these mechanisms are f a r too d i f f e r e n t to have had a common o r i g i n . Aquatic Hemiptera are s e c o n d a r i l y adapted to aquatic environment, and there i s some evidence that they a l l descended from a common an-ces t o r (China, 1955). However, i n aquatic Hemiptera, there are again s e v e r a l s t r i d u l a t o r y mechanisms (Dumortier, 1963 a ) , and since these are qu i t e d i f f e r e n t , i t i s apparent that s t r i d u l a t i o n i n these aquatic bugs has evolved independently s e v e r a l times. The f a m i l y Corixidae i s taxonomically subdivided i n t o s i x s u b f a m i l i e s . I t i s not known i f any s t r i d u l a t o r y appar-atus or song e x i s t i n the s u b f a m i l i e s Diaprepocorinae and Stenocorinae. The Cymatiinae (genus Cymatia) do not seem to have any s t r i d u l a t o r y organ, and no sounds have been recorded. European Micronectinae (genus Micronecta) are known to s t r i d -u l a t e ( M i t i s , 1936; Southwood and Leston, 1959), and the mechanism i s probably by use of the abdominal s t r i g i l ( M i t i s , 1936). However, American Micronectinae (genus Tenagobia) are sa i d to l a c k t h i s abdominal s t r i g i l (Hungerford, 1948). In 194 the Heterocorixinae records on s t r i d u l a t i o n are l a c k i n g , but according to the drawings i n Hungerford (1948) a l l species have a w e l l developed abdominal s t r i g i l i n males, and spec-i a l i s e d pegs are l o c a t e d at the p o s t e r i o r edge of the f i f t h abdominal te.rgum j u s t a n t e r i o r to the s t r i g i l : i t i s p o s s i b l e t h a t s t r i d u l a t o r y s i g n a l s are produced with t h i s apparatus, and thus u t i l i s e an apparatus s i m i l a r to that i n the European Micronectinae. C o r i x i n a e seems to be the only subfamily possessing a s t r i d u l a t o r y mechanism that i n v o l v e s s t r i d u l a t o r y pegs of the f r o n t femora and the m a x i l l a r y p l a t e . However, s t r i d -u l a t i o n i s not u n i v e r s a l i n C o r i x i n a e : s e v e r a l genera of t h i s subfamily are not able to s t r i d u l a t e , and i t i s not known whether they represent an advanced group that has l o s t the s t r i d u l a t o r y apparatus, or a p r i m i t i v e group that have not evolved i t . The existence of v a r i o u s d i f f e r e n t s t r i d -u l a t o r y mechanisms i n C o r i x i d a e , nevertheless, suggest t h a t s t r i d u l a t i o n i s not a plesiomorphic character, but r a t h e r an apomorphic one (Hennig,;. 1966) , one t h a t has evolved a f t e r s e p a r a t i o n of the s u b f a m i l i e s . The n o n - s t r i d u l a t i n g genera of Corixinae are thus p o s t u l a t e d never to have had a s t r i d -u l a t i r y a b i l i t y . Since C o r i x i n a e do not have a d i s t i n c t c o u r t s h i p d i s p l a y , i t i s not l i k e l y that the s t r i d u l a t o r y behavior has evolved i n the way suggested i n Orthoptera by Alexander (1962). An a l t e r n a t i v e e v o l u t i o n must be suggested, and r i t u a l i z a t i o n of "comfort" movements seems to be a p o s s i b i l i t y . Such r i t u a l i z a t i o n i s w e l l documented i n v e r t e b r a t e s (e.g. Huxley, 195 1914), but seems to be a p o s s i b i l i t y i n i n v e r t e b r a t e s as w e l l : waving d i s p l a y of f i d d l e r crabs (genus Uca) (Crane, 1966). In the C o r i x i n a e , each p a i r of legs has been adapted to serve a d i f f e r e n t primary f u n c t i o n : the f o r e legs f o r feeding, the middle legs f o r c l i n g i n g , and the hind legs f o r swimming. However, these legs a l s o have important sub-s i d i a r y f u n c t i o n s . I t w i l l be r e c a l l e d that the various species of Ceno-c o r i x a w i l l f r e q u e n t l y rub/the hind l e g s along the c o s t a l margin of the h e m i e l y t r a . This movement, which was o f t e n observed a f t e r the i n s e c t s had been handled, undoubtedly i s aimed at rearranging the l a t e r a l abdominal h a i r s that are very important i n maintaining the a i r bubble between the wings and the abdominal dorsum f o r r e s p i r a t i o n (Popham, I960; Parsons, 1970)- While t h i s i s c l e a r l y a "comfort" move-ment, i t i s a l s o a movement tha t produces sounds which have been i n t e r p r e t e d by some authors as s t r i d u l a t i o n (Moore, I 9 6 I ; Finke, 1968). In Cenocorixa i t was shown th a t such sounds do indeed have c e r t a i n c h a r a c t e r i s t i c s that are required i n a s t r i d u l a t o r y signal:,; but a l l species were observed to produce a comparable sound. At present they do not seem to serve as s t r i d u l a t o r y s i g n a l s i n Cenocorixa. However, true s t r i d u l a t o r y s i g n a l s could e a s i l y evolve from t h i s . S i m i l a r l y , the f r o n t l e g s , although used".and h i g h l y modified f o r feeding, a l s o are used i n c l e a n i n g movements, e s p e c i a l l y movements across the labium f o r "preening" the long sensory setae t h a t are l o c a t e d at i t s t i p (Lo and Acton, 196 1969). Such movements couild w e l l have been the precursor of the present day s t r i d u l a t o r y movements i n Cenocorixa and other s t r i d u l a t i n g C o r i x i n a e . Any two p a r t s of an exosceleton can be rubbed together to produce a noise, and so these movements could e a s i l y have become r i t u a l i s e d and the pa r t s modified. Another m o d i f i c a -t i o n i n the t h o r a c i c t r a c h e a l system could have l e d to the e v o l u t i o n of the sound r e c e i v i n g tympanum. In a s i m i l a r manner, movements of the s c l e r o t i z e d p a r ts of the abdomen during d e f a c a t i o n or mating or both could produce sounds which -likewise could have been s e l e c t e d i n European Micronectinae. A p a r a l l e l e v o l u t i o n i s a l s o sugg-ested i n He t e r o c o r i x i n a e . I t was noted i n Cenocorixa. that i n most species there i s only a s i n g l e type of s i g n a l i n each sex. In c o n t r a s t to t h i s , the Orthoptera have f r e q u e n t l y s e v e r a l d i f f e r e n t types of song t h a t appear to be s p e c i a l i s e d f o r p r e c i s e f u n c t i o n s . Thus, i n Orthoptera there are d i s t i n c t and d i f f e r e n t c a l l i n g , c o u r t s h i p , r i v a l ' s , e tc. songs. In Cenocorixa the var i o u s experiments undertaken suggest that i n some species (_C. b i f i d a , C_. dakotensis, _C. expleta) the same s i g n a l can f u n c t i o n as a c a l l i n g song and a g o n i s t i c song. In some other species (_C. b l a i s d e l l i , _C. wileyae) p a r t of t h e i r "normal" s i g n a l can be produced sep a r a t e l y , but no obvious f u n c t i o n of t h i s p a r t could be detected. Further, i n two species (_C. andersoni and _C. utahensis) p a r t of t h e i r "normal" c a l l seemed to have a d i f f e r e n t f u n c t i o n ( a g o n i s t i c song) from that of the "normal" c a l l ( c a l l i n g song). I t would appear that here we have evidence of the i n c i p i e n t e v o l u t i o n of s t r i d u l a t o r y d i v e r s i t y towards a more complex a c o u s t i c a l communication system. A g o n i s t i c s i g n a l s seem to be ev o l v i n g from a c a l l i n g s i g n a l , i.-.e. a double s t r i d u l a t o r y s i g n a l i s e v o l v i n g from a s i n g l e p r e - e x i s t i n g one. The Co r i x i n a e , and i n p a r t i c u l a r the genus Cenocorixa, can be considered on the e v o l u t i o n a r y t h r e s h o l d , o f s t r i d u l a t o r y d i v e r s i f i c a t i o n . 198 V. SUMMARY 1 . In the genus Cenocorixa both males and females prod-uce species and sex s p e c i f i c s t r i d u l a t o r y s i g n a l s : the sound i s produced by rubbing s p e c i a l i z e d s t r i d u l a t o r y pegs, l o c a t e d a n t e r o b a s a l l y on the f r o n t femora (pars s t r i d e n s ) , against the edge of the m a x i l l a r y p l a t e (plectrum). A c o r r e l a t i o n seems to e x i s t between the loudness of s i g n a l s and morphology of the s t r i d u l a t o r y apparatus. 2. S p e c i f i c d i f f e r e n c e s i n the s i g n a l s were found i n the temporal p a t t e r n of pulses, pulse r a t e , s t r u c t u r e of pulses, and s i g n a l l e n g t h . Change i n temperature a f f e c t s the pulse ra t e and, when a p p l i c a b l e , the pulse group r e p e t i t i o n r a t e , but not u s u a l l y the temporal p a t t e r n of pulses. 3 . Annual rhythm of s t r i d u l a t i o n i s c o r r e l a t e d w i t h sexual maturity. In males spontaneous s t r i d u l a t i o n commences when mature sperm occurs i n the t e s t e s : i n the s p r i n g , e a r l y summer, and i n l a t e f a l l . In areas where no freeze-up e x i s t s , the males s t r i d u l a t e throughout the winter. In females spon-taneous s t r i d u l a t i o n was never observed, but induced s t r i d -u l a t i o n commences when chorionated eggs are found i n the l a t e r a l oviducts and apparently no sperm e x i s t s i n the recept-aculum seminis. Sexual m a t u r i t y i n females i s only reached i n ifehelspring and e a r l y summer. 4. B e h a v i o r a l l y the s t r i d u l a t i o n of males seems to f u n c t i o n both as a c a l l i n g s i g n a l and as an a g o n i s t i c s i g n a l . The "female s i g n a l can be c l a s s i f i e d as an agreement s i g n a l f o r i t i s only produced by r e c e p t i v e females and a f t e r a s t r i d -u l a t o r y stimulus from the male. Recently mated females do 199 not s t r i d u l a t e and do not accept males attempting c o p u l a t i o n . 5. In most species the males answer almost any s t r i d -u l a t o r y s t i m u l i , but only the s i g n a l s of c o n s p e c i f i c females i n i t i a t e searching behavior i n the males. Females do not respond to male s i g n a l s of other species, but the response to c o n s p e c i f i c male s i g n a l s i s to stay s t a t i o n a r y and answer by s t r i d u l a t i n g . 6. S t r i d u l a t i o n f u n c t i o n s a,s a premating i s o l a t i n g mechanism i n the genus stu d i e d , but does n o t . c o n s t i t u t e the whole i s o l a t i n g mechanism. I t i s r e i n f o r c e d by geographic, and e c o l o g i c a l i s o l a t i o n i n a number of cases. 7 . I t i s suggested that the s t r i d u l a t o r y movements i n Cori x i d a e have a r i s e n by r i t u a l i z a t i o n of comfort movements. 8. The Corixidae are considered to represent a stage i n e v o l u t i o n at which d i v e r s i f i c a t i o n of s t r i d u l a t o r y s i g n a l s i s e v o l v i n g from a s i n g l e p r e - e x i s t i n g one. At the present time, most species have a s i n g l e male c a l l that can f u n c t i o n i n at l e a s t two contexts. 200 VI. LITERATURE CITED Alexander, R.D. 1962. E v o l u t i o n a r y change i n c r i c k e t a c o u s t i c a l communication. Syst. Zool. 11: 53-72,/ - " - 1964. 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Perdeck, A.C. 1 9 5 8 . The i s o l a t i n g value of s p e c i f i c song patterns i n two s i b l i n g species of grasshoppers (Chorthippus brunneus Thunb. and C_. b i g u t t u l u s L. ). Behaviour 12 : 1-75. 205 Pinder, A.R. and Staddon, B.W. 1965 a. Trans-4-oxohex-2-enal i n the odiferous s e c r e t i o n of S i g a r a f a l l e n i (Fieb.) (Hemiptera-Heteroptera). Nature, Lond. 205: 106-107. - " - 1965 b. The odiferous s e c r e t i o n of the water bug S i g a r a f a l l e n i ( F i e b . ) . J. Chem. Soc. 530: 2955-2958. Popham, E.J. i 9 6 0 . On the r e s p i r a t i o n of aquatic Hemiptera Heteroptera w i t h s p e c i a l reference to the C o r i x i d a e . Proc. Zool. Soc. Lond. 135: 209-242. - " - I 9 6 I . The f u n c t i o n of the p a l e a l pegs of Corixidae (Hemiptera Heteroptera). Nature, Lond. 190: 742-743. Rawson, D.S. and Moore, J.E. 1944. The s a l i n e lakes of Saskatchewan. Can. J. Res. (D) 22: 141-201. Remold, H. 1962. Uber die b i o l o g i s c h e bedeutung der Duft-drusen b e i den Landwanzen (Geocorisae). Z. v e r g l . P h y s i o l . 45: 636-694. Rensch, B. 1959- E v o l u t i o n above the species l e v e l . 419 pp. Methuen and Co.,Ltd., London. -Richards, O.W. 1961. The s o c i a l i n s e c t s . 219 pp. Harper and Brothers, New York. Roth, L.M. and Hartman, H.B. 1967. Sound production and i t s e v o l u t i o n a r y s i g n i f i c a n c e i n the B l a t t a r i a . Ann. Ent. Soc. Amer. 60: 740-752. Roth, L.M. and W i l l i s , E.R. 1952. A study of cockroach behavior. Am. M i d i . Nat. 47: 66-129. S c h a l l e r , F. 1951- Lauterzeugung und HftrvermGgen von Corixa ( C a l l i c o r i x a ) s t r i a t a L. Z: v e r g l . P h y s i o l . 33: 476-486. Scudder, G.G.E. 1964. Wing muscle polymorphism i n Cenocorixa. Am. Zool. 4: 331-332. - " - 1966. The Immature stages of Cenocorixa b i f i d a (Hung.) and C_. expleta;' (Uhler) (Hemiptera: C o r i x i d a e ) . J. ent. Soc. B r i t i s h Columbia 63: 33-40. - " - 1969 a. The d i s t r i b u t i o n of two species of Cenocorixa i n i n l a n d s a l i n e lakes of B r i t i s h Columbia. I b i d , 66: 32-41 - " - 1969 b. The fauna of s a l i n e lakes on the Fraser Plateau i n B r i t i s h Columbia. Verh. In t e r n a t . V e r e i n . Limnol. 17: 430-439. 206 Scudder, G.G.E. 1971. Comparative morphology of i n s e c t g e n i t a l i a . A. Rev. Ent. 16: ( i n p r e s s ) . S i e g e l , S. 1956. Nonparametric s t a t i s t i c s f o r the behavioral sciences. 312 pp. McGraw-Hill Co., New York. Southwood, T.R.E. and Leston, D. 1959. Land and water bugs of the B r i t i s h I s l e s . 436 pp. Fr. Warne and Co., London. Sparrow, R.A.H. 1966. Comparative limnology of lakes i n the southern Rocky Mountain trench, B r i t i s h Columbia. J. F i s h . Res. Bd.. Canada 23: 1875 - I 8 9 5 . S p i e t h , H.T. 19^7. Sexual behaviour and i s o l a t i o n i n Droso-p h i l a . I. The mating behaviour of species of w i l l i s t o n i group. E v o l u t i o n 1: 17-31. Spooner, J.D. 1964. The Texas bush katydaid - i t s sound and t h e i r s i g n i f i c a n c e . Anim. Behav. 12: 235-244. - " - 1968. P a i r - f o r m i n g a c o u s t i c systems of phaneropterine katydids (Orthoptera, T e t t i g o n i i d a e ) . Anim. Behav. 16: 197-212. S t r i c k b e r g e r , M.W. 1962. Experiments 1 i n genetics w i t h Drosophila. 144 pp. J. Wiley and Sons, New York. Thomson, M. 1894. S t r i d u l a t i o n of Corixa. I r . Nat. 3: 114-115. Van T a s s e l , E.R. 1965. An audiospectrographic study on s t r i d u l a t i o n as an i s o l a t i n g mechanism i n the genus Berosus (Coleoptera, H y d r o p h i l i d a e ) . Ann. ent. Soc. Am. 50: 407-413. Waldon, I. 1964. Courtship sound production i n two sympatric s i b l i n g D rosophila species. Science 144: 191-193. Walker, T.J. 1957- S p e c i f i t y i n the response of female t r e e c r i c k e t s (Orthoptera, G r y l l i d a e , Oecanthinae) to c a l l i n g songs of the males. Ann. Ent. Soc. Am. 50: 626-636. - " - 1962. Factors r e s p o n s i b l e f o r i n t r a s p e c i f i c v a r i a t i o n i n the c a l l i n g songs of c r i c k e t s . E v o l u t i o n 16: 407-428. Wasserman, A.O. 1957. Factors a f f e c t i n g i n t e r b r e e d i n g i n sym-p a t r i c species of spadefoots (genus Scaphiobus). Evo-l u t i o n 11: 320-338. Young, E.C. 1965. F l i g h t muscle polymorphism i n B r i t i s h C o r i x -idae: E c o l o g i c a l observations. J. Anim. E c o l . 34: 353-390. Zwart, K.W.R. 1965. On the i n f l u e n c e of some food substances on s u r v i v a l of C o r i x i d a e . ( H e t e r o p t e r a ) . X I I I n t . Congr. Ent., London: 411-412. 207 APPENDIX I SYSTEMATIC NOTES AND NEW SYNONYMY IN THE GENUS CENOCORIXA Hungerford (1948) i n h i s r e v i s i o n of the Corixidae of the western hemisphere, erected a new genus Cenocorixa i n which he placed nine species. Subsequently, Hungerford (1956) described a new species and more r e c e n t l y , Lansbury ( i 9 6 0 ) has described three a d d i t i o n a l species i n the genus. At the present time, Cenocorixa thus contains 13 described species. In the present study i t was discovered that there are only e i g h t d i s t i n c t species i n the genus; s e v e r a l of the p r e v i o u s l y described species must be re l e g a t e d to synonymy. In a d d i t i o n , while the published d e s c r i p t i o n s of the species are i n general adequate, the published f i g u r e s on s p e c i f i c d i f f e r e n c e s are not very accurate and the key i n Hungerford (1948) i s somewhat u n r e l i a b l e , since the characters u t i l i s e d are o f t e n r a t h e r v a r i a b l e . This Appendix thus r e v i s e s the v a l i d s pecies, gives the new synonymy, and presents a r e v i s e d key to males of the genus. A key to females of the genus i s i n p r e p a r a t i o n . Cenocorixa b i f i d a . (Hungerford) A r c t o c o r i x a b i f i d a Hungerford 1926, Can. Ent. 58: 268. Cenocorixa b i f i d a , Hungerford 1948, Univ. Kansas S c i . B u l l . 32: 569; red.escription. SYN. NOV. Cenocorixa hungerfordi Lansbury i 9 6 0 , Proc. ent. Soc. B. C. 57: 36. Cenocorixa b i f i d a , B r o o k s and K e l t o n 1967, Mem. Ent. 208 Soc. Canada 51: 24; r e d i s c r i p t i o n . Considerable geographic and i n t r a s p e c i f i c v a r i a t i o n was observed i n t h i s species. The d e s c r i p t i o n of the species by Hungerford (1948) must be ammended as f o l l o w s : The peg row of the male p a l a i s c l e a r l y broken i n specimens from A l b e r t a (as sta t e d by Hungerford, 1948), but i n specimens from northern Utah i t i s not so c l e a r l y broken, and i t i s u s u a l l y unbroken i n specimens from B r i t i s h Colum-b i a ( F i g . 6 8 ) . The r i g h t paramere i s not qu i t e as i n the drawing i n Hungerford (1948), and the shape of the more proximal p r o j e c t i o n v a r i e s from roundish i n A l b e r t a and Utah specimens to sharp i n B r i t i s h Columbia specimens ( F i g s . 71 and 7 2 ) : a l s o the shape of the s t r i g i l v a r i e s s l i g h t l y . Dorsal view of the p o s t e r i o r abdominal terga i s shown i n F i g . 6 4 . Lansbury ( i 9 6 0 ) described t h i s species under the name C_. hungerfordi from B r i t i s h Columbia, but apparently he was not aware of the e x i s t i n g v a r i a t i o n . I have cross mated specimens from A l b e r t a and B r i t i s h Columbia (to be published) and despite the d i f f e r e n c e s between the populations, the experiment showed that cross breeding was s u c c e s s f u l (at the moment the c u l t u r e s are i n the F^ generat i o n ) . Typo materia.liexamined: Holotype cf, a l l o t y p e $, and la* (paratype): :Lost Lake, A l b e r t a , Canada, (the paratype male studied belongs to C_. utahensis) [Univ. Kansas]. 4 cfcf and 8 ?$ of C_. hungerf o r d i Lansb., Kam-loops, B r i t i s h Columbia [U.B.C.]. A d d i t i o n a l m a t e r i a l : Canada, B r i t i s h Columbia, C h i l c o t i n , 209 Beeche's P r a i r i e - ; Kamloops, Lac du Bois area (LB2); A l b e r t a , Brooks. USA: Utah, Wasatch Co., Strawberry R e s e r v o i r . Cenocorixa k u i t e r t i Hungerford Cenocorixa k u i t e r t i Hungerford 1948, Univ. Kansas S c i . B u l l . 3 2 : ; : 5 7 1 . The tergum of the middle lobe of the seventh abdominal segment d o r s a l l y does not have a d i s t i n c t t u f t of h a i r s as shown i n Hungerford (1948), but only a few short h a i r s appear ( F i g . 6 4 ) . The arrangement of the p a l a r pegs i s shown i n F i g . 69, and some v a r i a t i o n of the shape of the r i g h t paramere i n F i g . 73. M a t e r i a l examined: USA: C a l i f o r n i a , Tuolumne Co., Tioga Pass (type l o c a l i t y ) . Cenocorixa andersoni Hungerford Cenocorixa, andersoni Hungerford 1948, Univ. Kansas S c i . B u l l . 32, 573. ^ZE* 2°J£* Cenocorixa m a l k i n i Hungerford 1956, J. Kansas ent. Soc. 29: 39. SYN.. NOV. Cenocorixa downesi Lansbury i 9 6 0 , Proc. ent. Soc. B. C. 57: 40. The o r i g i n a l d e s c r i p t i o n of Hungerford (1948) must be am-mended as f o l l o w s : Male abdomen d o r s a l l y has the median lobe of the tergum 7 more or l e s s d i s t i n c t l y separated from the l e f t lobe by a break, which i s sometimes c l e a r l y seen, but may a l s o be almost 210 n o n - e x i s t i n g . However, the two lobes are " t i e d " together w i t h a t u f t of h a i r s o r i g i n a t i n g from the l e f t lobe; the species thus has two h a i r t u f t s , a caudal l o n g i t u d i a l and a transverse one.(Fig. 6 5 ) . The s i z e of the transverse t u f t i s somewhat v a r i a b l e and the s i z e of the break between the l o b e s } i s p r o p o r t i o n a l to the s i z e of the t u f t . The l a s t segment of the hind l e g (tarsus 2) i s some-times dark brown, but sometimes the whole l e g i s l i g h t brown. Arrangement of the pegs of p a l a i s shown i n F i g . 69, and some i n t r a s p e c i f i c v a r i a t i o n of the r i g h t paramere i s shown i n F i g s . 71 and 73. Hungerford (1956) described t h i s species under the name C_. m a l k i n i apparently because he had not n o t i c e d the v a r i a t i o n i n the c o l o r of the tarsus 2; the specimens on which the o r i g i n a l C.. andersoni d e s c r i p t i o n was based, do not have a dark brown tarsus 2, w h i l e a l l C_. m a l k i n i type specimens I have seen, have dark brown tarsus 2. However, the c o l o r of the tarsus 2 seems to depend on the c o l o r of the bottom of the pond or l a k e : i n lakes w i t h dark bottom tarsus 2 i s dark brown, but i n pale bottom lakes i t i s l i g h t * . Lansbury ( i 9 6 0 ) based h i s d e s c r i p t i o n of C_. downesi on only one male specimen. He n o t i c e d the existence of the t r a n s -verse h a i r t u f t , but because the t i p of the median lobe of tergum V I I i s broken o f f , the specimen does not have any * For the e f f e c t of c o l o r of the bottom of lakes on Corixidae, see: Popham, E.J. 1941. The v a r i a t i o n i h colour of c e r t a i n species of A r c t o c o r i s a (Hemiptera, Corixidae) and i t s s i g n i f -i cance. Proc. Zool. Soc. Lond. I l l (A): 135-172. 211 caudal h a i r t u f t : Lansbury ( i 9 6 0 ) e v i d e n t l y d i d not n o t i c e t h a t the specimen was broken. Type m a t e r i a l examined: Holotype cf , 1 ? (paratype): Washington, Kalama R i v e r ; 1 cf (paratype): Oregon, Florence [Univ. Kansas]. _C. m a l k i n i : Holotype cf, a l l o t y p e ?, 7 oV and 1 ? (paratypes): Washington, Chase Lake, Snohomish Co. [Univ. Kansas, and C a l i f . Acad. S c i ] . 1 cf (paratype): Oregon, Florence [Mnivs-Kansas ]. downesi: holotype cf: B r i t i s h Columbia, Vancouver. A d d i t i o n a l m a t e r i a l : Canada: B r i t i s h Columbia, Spec-t a c l e Lake, Vancouver I s l a n d [ C a l i f . Acad. S c i . , c o l l . J . Simpson]; Vancouver, Stanley Park; White Rock, roadside pond; Abbotsford, Trout Hatchery pond ( c o l l . J. Ryan). USA: Wash-ington, Whatcom Co., Custer. Cenocorixa utahensis (Hungerford) A r c t o c o r i x a utahensis Hungerford 1925, B u l l . Brooklyn Ent. Soc. 20: 22. Cenocorixa utahensis, Hungerford 1948, Univ. Kansas S c i B u l l . 32: 58O; r e d e s c r i p t i o n . Cenocorixa utahensis, -Brooks.and K e l t o n 1967, Mem. Ent. Soc. Canada 51: 25; ' red.e.script!on,V, The m a t e r i a l studied agreed w i t h the d i s c r i p t i o n i n Hun-g e r f o r d (1948). However, the drawing on the r i g h t paramere i n Hungerford (1948) i s s l i g h t l y m i s l e a d i n g , and v a r i a t i o n i n the shape of t h i s i s shown i n F i g s . 71 and 74. Dorsal view of p o s t e r i o r abdominal terg a i s shown i n F i g . 65, and arrangement of the p a l a r pegs i n F i g . 69. 212 Type m a t e r i a l examined: Holotype cf, a l l o t y p e $, 2 cfcf 3 $$ (paratypes): Utah, Emery Co., [Univ. Kansas]. A d d i t i o n a l m a t e r i a l : Canada, A l b e r t a , Gleichen; Brooks; Medicine Hat. USA: Washington,Franklin Co., Mesa; F r a n k l i n Co., Kootenay Re s e r v o i r ; Utah, G a r f i e l d Co., Hatch; Duchesne Co., S t a r v a t i o n R e s e r v o i r ; Cenocorixa dakotensis (Hungerford) A r c t o c o r i x a dakotensis Hungerford 1928, Can. Ent. 60: 229. Cenocorixa dakotensis, Hungerford 1948, Univ. Kansas S c i . B u l l . 32: 567; red.escription. Cenocorixa dakotensis, Brooks and K e l t o n 1967, Mem. Ent. Soc. Canada 51: 23;;' r e d e s c r i p t i o n ; , The m a t e r i a l studied agreed wi t h the d e s c r i p t i o n i n Hun-ge r f o r d (1948), except that some v a r i a t i o n i n the shape of the r i g h t paramere was observed, and i s shown i n F i g s . 71 and 74. Dorsal view of p o s t e r i o r abdominal terga i n male i s shown i n F i g . 66, and arrangement of p a l a r pegs i n F i g . 69. M a t e r i a l studied: Canada, A l b e r t a , Gleiche; Brooks; Medicine Hat. Cenocorixa b l a i s d e l l i (Hungerford) A r c t o c o r i x a b l a i s d e l l i Hungerford 1930, Pan-Pacif. Ent. 7: 26. S i g a r a b l a i s d e l l i , Jaczewski 1931, Arch. Hydrobiol. 23: 511. 213 Cenocorixa b l a i s d e l l i , Hungerford 19^8, Univ. Kansas S c i . B u l l . 32: 57^; r e d e s c r i p t i o n . SYN. NOV. Cenocorixa columbiensis Lansbury i 9 6 0 , Proc. ent. Soc. B. C. 57: 38. Hungerfordis (19^8) d e s c r i p t i o n should be ammended to • sta t e that the seventh abdominal tergum of males has three caudal p r o j e c t i o n s ( F i g . 6 6 ) ; the r i g h t paramere i s as shown i n F i g s . 71 and 'Jk. Arrangement of p a l a r pegs i s shown i n F i g . 70. Lansbury ( i 9 6 0 ) described t h i s species from B r i t i s h Columbia under the name C_. columbiensis. He a l s o gave draw-in g s , which, however, do not agree w i t h h i s type specimens. He apparently d i d not recognise the specimens as C_. b l a i s -d e l l i (Hungfd.), because Hungerford (19^8) records the l a t t e r only from C a l i f o r n i a . However, Hungerford (1948) gives a reference to Jaczewski (1931), and i n the l a t t e r the species i s recorded from Washington. Apparently the species occurs a l l along the coast from B r i t i s h Columbia to C a l i f o r n i a , although no record from Oregon has been published. Specimens from B r i t i s h Columbia and C a l i f o r n i a do not show any apparent geographic v a r i a t i o n . Type m a t e r i a l examined: 3 cfcf (paratypes): Vine H i l l , Contra Costa Co., C a l i f o r n i a [Univ. Kansas]; 2 rfc? 1 $ (paratypes): Berkeley, C a l i f o r n i a [ C a l i f . Acad. S c i . ] (one of the male paratypes has a female C o r i s e l l a decolor (Uhler) mounted on the same p i n ) . C_. c o l -umbiensis Lansb. : holotype cf, a l l o t y p e ?, 5 cftf 5 ?? (para-t y p e s ) : Pond, Univ. B r i t . C o l . , B r i t i s h Columbia [U.B.C.]. 214 A d d i t i o n a l m a t e r i a l : Canada, B r i t i s h Columbia, Vancouver, Stanley Park; U.B.C. area. USA: C a l i f o r n i a , San Mateo Co., San F r a n c i s c o ; Humboldt Co., Calm Beach. Cenocorixa wileyae (Hungerford) A r c t o c o r i x a wileyae Hungerford 1 9 2 6 , Can. Ent. 5 8 : 2 7 1 . Cenocorixa wileyae, Hungerford 19^8, Univ. Kansas S c i . B u l l . 3 2 : 5 7 8 ; r e d e s c r i p t i o n . The shape of the r i g h t paramere i s as i n F i g s . 71 and 75? and not as shown i n Hungerford ( 1 9 4 8 ) . Dorsal view of p o s t e r i o r abdominal terga of male i s shown i n F i g . 6 7 , arrangement of p a l a r pegs i n F i g . 7 0 . M a t e r i a l studied: USA: Washigton, F r a n k l i n Co., 0 ' S u l -l i v a n dam area; Oregon, Sherman Co., Kent; Deschutes Co., La Pine; C a l i f o r n i a , Modoc Co., Newell; Lassen Co., Said Lake; Doyle; A l p i n e Co., Monitor Pass; Mono Co. and Tuolumne Co., Tioga Pass; Mono Co., Black Lake; Nevada, Nye Co., R a i l r o a d V a l l e y ; Utah, G a r f i e l d Co., Hatch; Duchesne Co., S t a r v a t i o n Res.; Wasatch Co., Strawberry Res., Cenocorixa e x p l e t a (Uhler) Co r i s a e x p l e t a Uhler 1 8 9 5 , ( i n ) G i l l e t t e , C. P. and Baker, C. F.: Hemiptera of Colorado, Colorado Agr. Exp. St. B u l l . 3 1 , Tech. ser. 1: 6 3 . A r c t o c o r i s a e x p l e t a , K i r k a l d y and Torre-Bueno 1 9 0 9 , Proc. Ent. Soc. Wash. 1 0 : 195 . Cenocorixa e x p l e t a , Hungerford 19^8, Univ. Kansas 215 S c i . B u l l . 32: 576; r e d e s c r i p t i o n . Cenocorixa e x p l e t a , Brooks and K e l t o n 1967, Mem. Ent. Soc. Canada 51: 24; r e d e s c r i p t i o n . No major d i f f e r e n c e s were detected between the r e d e s c r i p -t i o n of Hungerford (1948) and the m a t e r i a l studied. S l i g h t v a r i a t i o n was observed i n the shape of the r i g h t paramere ( F i g s . 71 and 75)- Dorsal view of male abdomen i s shown i n F i g . 67 and male p a l a i s shown i n F i g . 70. M a t e r i a l s tudied: Canada, B r i t i s h Columbia, Kamloops area (LB2); Okanagan V a l l e y , F a l k l a n d . USA, Washington, Grant Co., Soap Lake. Si g a r a nevadensis (Walley) Argtocorixa.'nevadeHsls Walley 1936, Can. Ent. 68: 58. Sigara (Vermicorixa) nevadensis, Hungerford 1948, Univ. Kansas S c i . B u l l . 32: 704; r e d e s c r i p t i o n . SYN. NOV. Cenocorixa sorensoni Hungerford 1948, Univ. > S ^ S / S « . * * * * * * Kansas S c i . B u l l . 32: 565. In a d d i t i o n to the Cenocorixa species above, Hungerford (1948) described C_. sorensoni i n h i s monograph:f r.om m a t e r i a l c o l l e c t e d from Brigham, Utah. However, i n the g e n e r a l - d e s c r i p -t i o n of the genus Cenocorixa, Hungerford (1948) was forced to make an exception i n C_. sorensoni females: the l a s t v e n t r a l abdominal segment i s i n c i s e d at t i p i n a l l other species. In a d d i t i o n , C_. sorensoni appears to be c l e a r l y smaller than other species of the genus, and the median l o n g i t u d i n a l c a r i n a of the pronotum i s very short. A l s o the c l a v a l p a t t e r n i s 216 d i f f e r e n t from other Cenocorixa species: i n C_. sorensoni the transverse pale l i n e s are enlargened i n the middle of the clavus w h i l e i n a l l other species the l i n e s are vermiculate, but not enlargened. A l s o the male p a l a i n C_. sorensoni has a ri d g e i n the middle, which does not appear i n any other Cenocorixa species. A l l these "exceptions" would place C_. sorensoni i n the genus Si g a r a . Indeed the species i s placed i n t h i s genus i n Hungerford (1948) under the name S_. neva-densis, although the o r i g i n a l d e s c r i p t i o n placed i t i n the genus A r c t o c o r i x a (Walley, 1936). " . The d e s c r i p t i o n s and f i g u r e s of S_. nevadensis and. C_. sorensoni i n Hungerford (1948) are very s i m i l a r and no a d d i t i o n a l d e s c r i p t i o n or f i g u r e i s needed. Some i n t r a s p e c -i f i c v a r i a t i o n was found i n the shape of the r i g h t paramere: the thickness of the d i s t a l p r o j e c t i o n v a r i e s s l i g h t l y . Type m a t e r i a l examined: Holotype cf, a l l o t y p e ?, 4 cfcf j ?? (paratypes): Humboldt R i v e r , Nevada [Am. Mus. Nat. H i s t . ] , 1 cf l $ (paratypes): as above [Univ. Kansas]. C_. sorensoni: holotype cf, a l l o t y p e $, 5 ^ (paratypes): Utah, Brigham [Univ. Kansas], 2 cfcf 2 ?? (paratypes): as above [Utah State U n i v . ] . A d d i t i o n a l m a t e r i a l : Utah, Box El d e r Co., Bear R i v e r . I d e n t i f i c a t i o n of Cenocorixa species i s d i f f i c u l t and some p r a c t i c e i s needed f o r c o r r e c t r e s u l t s . In males the i d e n t i f i c a t i o n has to be based mostly on the s t r u c t u r e of the abdominal dorsum ( 7 t h segment), and the shape of the r i g h t paramere. Females are more d i f f i c u l t , and no s u i t a b l e key 217 i s a v a i l a b l e so f a r . A key f o r the males i s as f o l l o w s : 1 (2) Pal'a w i t h the peg row sharply curved ( F i g . 70 b ) . . . . _C. wileyae 2 (1) P a l a w i t h the peg row not sharply curved 3 3 (4) Pala w i t h spinose tumescence at base ( F i g . 70 c ) . . . . C_. e x p l e t a 4 (3) P a l a without a tumescence at the base 5 5 (8) Right paramere not b i f u r c a t e . . . . 6 6 (7) Seventh abdominal tergum d o r s a l l y w i t h a caudal and transverse t u f t of h a i r s ( F i g . 65 A) C_. andersoni 7 (6) Seventh abdominal tergum d o r s a l l y w i t h only caudal t u f t of h a i r s ( F i g . 66 B) . .. . C_. b l a i s d e l l i 8 (5). Right paramere b i f u r c a t e . . . . . 9 9 (10) Hind l e g w i t h the l a s t segment (tarsus 2) e n t i r e l y black or dark brown, r i g h t paramere with-the proximal p r o j e c t i o n much thi n n e r than the d i s t a l p r o j e c t i o n ( F i g . 71 e) C_. dakotensis 10 (9) Combination of characters not as above 11 11 (12) Median lobe of the ':(tli• abdomina 1 , t e r gurn d o r s a l l y without a h a i r t u f t , at most a few short h a i r s appear ( F i g . 64 B), d i s t a l p r o j e c t i o n of the r i g h t paramere i r r e g u l a r l y curved at the t i p ( F i g , 71 b ) , proximal p r o j e c t i o n roundish C_. k u i t e r t i 12 (11) Combination of characters not as above 13 13 (14) P o s t e r i o r pegs of hind femur i n 2-3 rows or i n a clump, t h e i r number more than 12, p a l a r pegs oft e n i n a broken or almost broken row C. b i f i d a 218 14 (13) P o s t e r i o r pegs of hind femur u s u a l l y i n one row, t h e i r number l e s s than 12 , p a l a r pegs i n a r e g u l a r row _C. utahensis 219 a F i g . 6 4 . Dorsal view of p o s t e r i o r abdominal terga of male i n C. b i f i d a (A) and C. k u i t e r t i (B). 219 b 220 a F i g . 6 5 . Dorsal view of p o s t e r i o r abdominal terga of male i n C_. andersoni (A) and C_. utahensis. B 221 a P i g . 66. Dorsal view of p o s t e r i o r abdominal terga of male i n C. dakotensis (A) and C_. b l a i s d e l l i (B). 221 b 222 a F i g . 67 . Dorsal view of p o s t e r i o r abdominal terga of male i n _C. wileyae (A) and _C. exp l e t a (B). 223 a F i g . 6 8 . I n t r a s p e c i f i c v a r i a t i o n i n arrangement of p a l a r pegs i n C_. b i f i d a . Specimens from A l b e r t a ( a ) , Utah ( b ) , and B r i t i s h Columbia ( c , d). 224 a F i g . 69. Arrangement of p a l a r pegs i n _C. k u i t e r t i (a), _C. andersoni ( b ) , C_. utahensis ( c ) , and C_. dakotensis (d). 225 a F i g . 70. Arrangement of p a l a r pegs i n C. b l a i s d e l l i ( a ) , C_. wileyae ( b ) , and C. e x p l e t a ( c ) . 225 b 226 a F i g . 7 1 . T y p i c a l shapes of the r i g h t parameres i n Cenocorixa species, a - C_. b i f i d a ; b = C. k u i t e r t i ; c = £. andersoni; d = _C. utahensis; e = C_. dakotensis; f = C_. b l a i s d e l l i ; g = _C. wileyae; h = C_. e x p l e t a . 226 b 2 2 7 a F i g . 7 2 . I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere i n C. b i f i d a . Specimens from B r i t i s h Colum-b i a , C h i l c o t i n , Beeche's P r a i r i e , Lake Lye (a-d); B r i t i s h Columbia, Cariboo, Long Lake (e-h); Utah, Wasatch Co., Strawberry Reservoir ( i - j ) ; A l b e r t a , Brooks ( k - l ) . 2 2 8 a F i g - 73- I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere of C_. k u i t e r t i (a-d) (specimens from: C a l i f o r n i a , Tuolumne Co., Tioga Pass) and £. andersoni (e-1) (specimens from: Washington, Whatcom Co., Custer). 228 b 2 2 9 a F i g , 74. I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere i n C_. utahensis (a-d) (specimens from: a = A l b e r t a , Gleichen; b-c = A l b e r t a , Medicine Hat; d = Washington, F r a n k l i n Co., Scootenay R e s e r v o i r ) , _C. dakotensis (e-h) (specimens from: A l b e r t a , Brooks), and C_. b l a i s d e l l i ( i - l ) (specimens from: i - k = B r i -t i s h Columbia, Vancouver; 1 = C a l i f o r n i a , Humboldt Co., Clam Beach). 2 3 0 a F i g . 7 5 • I n t r a s p e c i f i c v a r i a t i o n i n shape of r i g h t paramere i n C_. wileyae (a-d) (specimens from: C a l i f o r n i a , Lassen Co., Said Lake) and C_. expleta (e-h) (specimens from: B r i t i s h Columbia, Kamloops area, LB2). 231 APPENDIX I I AUDIOSPECTROGRAPHIC ANALYSIS OF THE STRIDULATORY SIGNALS OF SOME NORTH AMERICAN CORIXIDAE FOUND SYMPATRIC WITH CENOCORIXA Various genera and species of Corixidae were found sym-p a t r i c w i t h Cenocorixa during the present study. Since some of these other species were observed to s t r i d u l a t e , the s i g n a l s of these were recorded and used i n playback: exper-iments w i t h Cenocorixa (see Table X I I , page 134). A n a l y s i s of the s i g n a l s of the other taxa showed that these c a l l s are species s p e c i f i c and d i f f e r e n t from Cenocorixa c a l l s . The l o c a l i t i e s where other s t r i d u l a t i n g C o r ixidae were found sympatric w i t h Cenocorixa, and the s i g n a l s of these taxa are as f o l l o w s : C o r i s e l l a t a r s a l i s (Fieber) Sympatric s i t u a t i o n s were: C_. b i f i d a , A l b e r t a ; _C. utahen-s i s , A l b e r t a , Utah; C_. dakotensis, A l b e r t a ; C_. wileyae, C a l i -f o r n i a , Nevada, Utah; C_. ex p l e t a , A l b e r t a . Male c a l l : ( F i g . <7;6 A): Recorded at 24.0°C. B a s i c a l l y a simple m u l t i p u l s a t e s i g n a l . However, the s i g n a l s are u s u a l l y produced i n a sequence of 3-10 short c a l l s , each l a s t i n g approximately 0.5-2 seconds at 24°C. The f i r s t c a l l s are u s u a l l y shorter than the l a t e r ones. Pulse r a t e at the given temperature i s about 60 pulses per second. Main frequency area of the sound i s 3-5 kc/sec. Female c a l l was not obtained. 232 Genus C a l l i c o r i x a The s i g n a l s of a l l C a l l i c o r i x a species obtained were found to be b a s i c a l l y of the same type with two p a r t s : f a i n t slow beginning which a c c e l e r a t e s to a louder and f a s t e r end-i n g . Main frequency area i n a l l s i g n a l s recorded was 3-5 kc/ sec. Only male c a l l s were obtained. _C. v u l n e r a t a ( U h l e r ) . Sympatric s i t u a t i o n s were: _C. b i -f i d a , B r i t i s h Columbia; C.. andersoni, B r i t i s h Columbia, Wash-ington; C. b l a i s d e l l i , B r i t i s h Columbia, C a l i f o r n i a . Male c a l l ( F i g . 76 B ) : Recorded at 23.2°C. Both parts of the c a l l are r e l a t i v e l y short and of simple m u l t i p u l s a t e type wi t h d i s t i n c t pulse i n t e r v a l s . Duration of the f i r s t p a r t at 23.2°C was about 0.7 seconds and the second part about 0.3 seconds. The f i r s t p a r t c o n s i s t s of somewhat i r r e g u l a r .pulses. Pulse r a t e of the f i r s t p a r t was about 12 and the second part about 28 pulses per second at the given temperature, C_. audeni Hungerford. Sympatric s i t u a t i o n s were: C_. b i -f i d a , B r i t i s h Columbia, A l b e r t a ; _C. k u i t e r t i , C a l i f o r n i a ; C_. utahensis, A l b e r t a ; C_. dakotensis, A l b e r t a ; C_. wileyae, C a l i f o r n i a ; _C. ex p l e t a , B r i t i s h Columbia, A l b e r t a . Male c a l l ( F i g . 77 A): Recorded at 22.5°C C. audeni c a l l i s much longer i n d u r a t i o n than that of _C. v u l n e r a t a : the f i r s t p a r t l a s t s about 1.5 seconds and the second part about 1.0 seconds at 22.5°C. Pulse rates at the given tem^ perature f o r the f i r s t and the second p a r t s are about 20 and 30 pulses per second, r e s p e c t i v e l y , _C. t e t o n i Hungerford. Sympatric s i t u a t i o n s were: _C. b i -f i d a , Utah; C_. utahensis, Utah (not i n the same l a k e , but i n 233 the same geographic area); _C. wileyae, Utah. Male c a l l ( F i g . 77 B): Recorded at 22.0°C. Only one s a t i s f a c t o r y r ecording made. According to t h i s the f i r s t p a r t of the c a l l i s very f a i n t and nothing can be stated about i t s l e n g t h . The second part of the c a l l i s of t y p i c a l C a l l i c o r i x a s i g n a l form. Duration of the second part i s about 0.5 seconds and the pulse r a t e about 34 pulses per second at 22.0°C. Genus Si g a r a Several species of the genus were found sympatric w i t h Cenocorixa, but only two of these species were observed to s t r i d u l a t e . S_. omani (Hungerford). Sympatric s i t u a t i o n s were: C_. k u i t e r t i , C a l i f o r n i a ; _C. andersoni, B r i t i s h Columbia, Wash-ingt o n ; C_. b l a i s d e l l i , B r i t i s h Columbia; C_. wileyae, C a l i f -o r n i a . Male c a l l ( F i g . 78 A): Recorded at 21.2°C. Simple m u l t i -p u l s a t e c a l l w i t h s l i g h t l y f a i n t e r beginning than the end and w i t h very short, almost n o n - e x i s t i n g pulse i n t e r v a l s . Duration of the s i g n a l i s about 1.5 seconds and pulse r a t e about 24 pulses per second at the given temperature. Main frequency area i s about 4-5 kc/sec. Only male c a l l was obtained f o r the species. S_. nevadensis (Walley). Sympatric s i t u a t i o n s were: _C. b i f i d a , Utah; C_. utahensis, Utah; C_. wileyae, Utah. However, _S. nevadensis d i d not occur i n the :same...lakes'iwith ariy'.lof the mentioned Cenocorixa species, but was found i n the same geo-234 graphic area. Male c a l l ( F i g . 78 B): Recorded at 22.2°C. Very much l i k e the c a l l of _S. omani, w i t h s l i g h t l y f a i n t e r beginning than the end, but i n S_. nevadensis c a l l the pulse i n t e r v a l s are d i s t i n c t . Duration of the s i g n a l was about 1.5 seconds and pulse rate about 22 pulses per second at the given tem-perature. Main frequency area of the sound i s 4-5 kc/sec. Female c a l l ( F i g . 78 C): Recorded at 21.0°C. A simple m u l t i p u l s a t e s i g n a l which i s much f a i n t e r than the male s i g n a l . Pulse i n t e r v a l s are d i s t i n c t , but some i r r e g u l a r i t i e s occur. Duration of the s i g n a l was about 2.5 seconds and pulse r a t e about 16 pulses per second at the given temperature. Main frequency area of the sound i s 4-5 kc/sec. The f u n c t i o n of the male and female s i g n a l s i n _S. neva-densis was observed to be to f a c i l i t a t e p a i r formation, i . e . the f u n c t i o n of the s i g n a l s seems to be the same as i n the genus Cenocorixa. 235 a F i g . 76. Sound spectrograms of the male c a l l s of C o r i s e l l a t a r s a l i s (A) and C a l l i c o r i x a v u l n e r a t a (B). _C. t a r s a l i s s i g n a l recorded at 24.0°C, specimen from: Utah, Box E l d e r Co., Bear R i v e r . C_. v u l n e r a t a s i g n a l recorded at 23.2°C, specimen from: B r i t i s h Columbia, Vancouver. F i g . 77. Sound spectrograms of the male c a l l s of C a l l i c o r i x a audeni (A) and C_. t e t o n i (B). CJ. audeni s i g n a l recorded.;at 22.5°C, specimen from: A l b e r t a , Brooks. C_. t e t o n i s i g n a l recorded at 22.0°C, specimen from: Utah, Wasatch Co., Strawberry Rese r v o i r . 235 b O O M « 3H 1 i i i i i i i i l i ! i 1 S E C O N D S 76 1 S E C O N D S 77 1 3 5 i Q fe O 3 o w w 1 w Hi u o M B " T " 2 S E C O N D S 236 F i g . 7 8 . Sound spectrograms of the s i g n a l s of Sigara  omani (A) and S_. nevadensis (B = male c a l l , C = female c a l l ) . S_. omani s i g n a l recorded at 21.2°C, specimen from: Washington, Whatcom Co., Custer. S_. nevadensis s i g n a l s recorded at 22.2°C (male) and 21.0°C (female), specimens from: Utah, Box E l d e r Co., Bear R i v e r . 

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