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Studies of some aspects of behaviour in the ambrosia beetle, Trypodendron lineatum (Olivier) Francia, Faustino C. 1965

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The U n i v e r s i t y  of B r i t i s h  Columbia  FACULTY OF GRADUATE STUDIES  PROGRAMME OF THE FINAL ORAL FOR THE  EXAMINATION DEGREE OF  DOCTOR OF PHILOSOPHY  of  FAUSTINO CAJUCOM FRANCIA  B.SoF., U n i v e r s i t y M,S.j  of t h e P h i l i p p i n e s , 1952  S t a t e U n i v e r s i t y of New York, C o l l e g e of F o r e s t r y a t Syracuse U n i v e r s i t y , 1957  FRIDAY, JULY 16, 1965, AT 10:30 A.M. IN ROOM 3332, BIOLOGICAL SCIENCE BUILDING  COMMITTEE IN CHARGE Chairman:  J . A, F. Gardner  J„ J„ R. Campbell K. Graham W. S. Hoar External  Examiner:  0. S z i k l a i J . W. W i l s o n D. J . Wort A. J . T h o r s t e i n s o n  Department of Entomology U n i v e r s i t y of Winnipeg Winnipeg, Manitoba  STUDIES OF SOME.ASPECTS OF BEHAVIOUR IN THE AMBROSIA BEETLE TRYPODENDRON LINEATUM (OLIVIER) ABSTRACT Behaviour p a t t e r n s of the ambrosia b e e t l e T r ^ E S ^ S S " dron lineatum. (Olivier) were s t u d i e d -in r e l a t i o n to v a r i o u s i n f l u e n c e s of i l l u m i n a t i o n , temperature, g r a v i t y , atmosp h e r i c p r e s s u r e and h o s t . f a c t o r s . The b e e t l e s were i n the overwintered, r e p r o d u c t i v e l y mature s t a t e i n which they a r e prepared f o r t h e i r normal f u n c t i o n s of emergence, f l i g h t d i s p e r s a l , h o s t - d i s c o v e r y and a t t a c k . Experiments were c o n f i n e d t o the study of the b e e t l e s i n p e d e s t r i a n situations, T h e i r responses were s t u d i e d b o t h b e f o r e and a f t e r being g i v e n f l i g h t e x p e r i e n c e . Before f l i g h t the m a j o r i t y of i n d i v i d u a l s are s t r o n g l y p h o t o p o s i t i v e at temperatures i n the range of 5 t o 36°C, the optimum b e i n g between 20° and 26°C. They become p r o g r e s s i v e l y p h o t o n e g a t i v e as temperatures r i s e above 26°C, u n t i l a l l i n d i v i d u a l s shun the l i g h t at 40 C. The e f f e c t i s r e v e r s i b l e as temperatures r e t u r n to optimum. A f t e r a p e r i o d of f l i g h t the p h o t o p o s i t i v e r e a c t i o n i s weakened, n u l l i f i e d , or r e p l a c e d by a negat i v e r e a c t i o n i n some, but not a l l i n d i v i d u a l s , A change i n t h r e s h o l d of response to l i g h t becomes most c l e a r l y manifest i n the presence of a t t r a c t i v e host odour. When a p h o t o p o s i t i v e r e a c t i o n occurs, i t i s r e t a i n e d r e g a r d l e s s of the d i r e c t i o n of the e a r t h ' s g r a v i t a t i o n a l f i e l d i n r e l a t i o n to the l i g h t source. The photop o s i t i v e response i s not a l t e r e d by two atmospheres pressure. A response t o host odour becomes m a n i f e s t under t h r e e d i f f e r e n t s i t u a t i o n s - (1) Female b e e t l e s bore i n t o wood which i s i t s e l f a t t r a c t i v e or i s made so by a p p l i c a t i o n of a t t r a c t i v e wood d i s t i l l a t e . This reaction i s d i s p l a y e d by f l i g h t - e x p e r i e n c e d b e e t l e s i n i l l u m i n a t e d or n o n - i l l u m i n a t e d s i t u a t i o n s , or by non-flown b e e t l e s i n darkness. (2) Males or females d i s p l a y a c e n t r i p e t a l response i n a f i e l d of odour a r i s i n g through a substratum. They t r a c e a meandering path f o r a prolonged p e r i o d , and r e p e a t e d l y r e t r i e v e t h e i r g e n e r a l p o s i t i o n when they t r a n s g r e s s beyond the boundary of the odour f i e l d . T h i s r e a c t i o n i s d i s p l a y e d under i l l u m i a t e d c o n d i t i o n s by f l i g h t - e x p e r i e n c e d b e e t l e s . (3) Males or females respond a n e m o t a c t i c a l l y to a i r streams c a r r y i n g a t t r a c t i v e host  odour. T h i s r e a c t i o n i s d i s p l a y e d under i l l u m i n a t e d c o n d i t i o n s by f l i g h t - e x p e r i e n c e d b e e t l e s . The e f f e c t of f l i g h t e x p e r i e n c e on p h o t i c r e sponses i s not a l l - o r - n o n e but a p p a r e n t l y i n v o l v e s a r i s e of t h r e s h o l d t o l i g h t i n t h e presence of a t t r a c t i v e host odour, or a lowering of t h r e s h o l d t o host: odour i n the presence of l i g h t . s  The non-response of the b e e t l e s t o green wood from a l i v i n g t r e e , and t h e continued response t o mixtures of green and a t t r a c t i v e wood i n d i c a t e that n e i t h e r a t t r a c t a n t s nor r e p e l l e n t s a r e present i n the l i v i n g tree. I t i s i n f e r r e d that s u s c e p t i b i l i t y of dying t r e e s to t h i s ambrosia b e e t l e owes i t s e l f t o chemical changes d u r i n g the death p r o c e s s . Since both sexes r e a c t t o the odours, i t i s i n f e r r e d t h a t i n i t i a l a t t a c k on a t r e e i n v o l v e s a primary a t t r a c t a n t from t h e h o s t . •Implications a r e seen f o r t h e r o l e of b e h a v i o u r i n the ecology of t h i s i n s e c t , Other i m p l i c a t i o n s a r e seen f o r the use of the newly a c q u i r e d i n f o r m a t i o n i n b i o a s s a y techniques i n which the i n s e c t w i l l serve as a t e s t instrument f o r chemical s t u d i e s of host a t t r a c t a n t s .  GRADUATE STUDIES Field  of Study:  Forest  Entomology  S t a t i s t i c a l Methods i n F o r e s t Research F o r e s t r y Seminar T o p i c s i n Wood Anatomy Biochemistry Experimental Zoology Directed Studies Zoology  J . H. G. Smith Forestry Staff J . W. W i l s o n J„ R. Campbell W. S. Hoar K. Graham  PUBLICATIONS F r a n c i a , F. C. & Snyder, T. E. I960,, A summary of P h i l i p p i n e t e r m i t e s w i t h supplementary b i o l o g i c a l notes. P h i l i p p i n e J . S c i . 89(1): 63-77. F r a n c i a , F. C. 1960. P r o t e c t i n g b u i l d i n g s from t e r m i t e and fungus damage. FPRI T e c h n i c a l Note No. 10, 1-4. F r a n c i a , F. C. 1960. S t u d i e s on the c o n t r o l of ambrosia b e e t l e s which damage newly-cut t i m b e r . P h i l . Lumberman, 6(2): 5-7. F r a n c i a , F. C„ 1958. Powderpost b e e t l e s (bukbok) i n j u r i o u s t o wood and other f o r e s t p r o d u c t s . P h i l . Lumberman, 4_(2) : 6-et seq. F r a n c i a , F. C. 1957. P i n h o l e s i n logs and lumber. P h i l . Lumberman, _3(5): 16-18.  STUDIES QP SOME ASPECTS OP BEHAVIOUR IK THE AMBROSIA. BEETLE TRYP033EMDR01I LINEATUM (OLJ.\^im)  by FADSTINO C FBAHCIA. B»S«F«, University of the Biilipjgines, 1952 M.S. j, State University of Hew York, College of Fbnastfcry at Syracuse University, 1957  A THESIS SUBMITTED US EAHHAL FULSILME1C2 OF THS 1  REQUIREMENTS FOR THE I3BGRKB. OF Doctor of Riilosophy i n the Faculty of  We accept this thesis as conforming to the required standard  THE UNHERSITY OF BRITISH GOIUMBIA. JtQy, 1965  In p r e s e n t i n g the  r e q u i r e m e n t s f o r an  British  Columbia,  available for mission  representatives,,  cation  of  w i t h o u t my  this  by  v  the  7  Columbia  of  University  of  s h a l l make i t  thesis  Head o f my  permission.  fulfilment  I f u r t h e r agree that  this  for financial  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada^ Date  study.  the  Library  It i s understood  thesis  written  the  copying of  granted  in p a r t i a l  advanced degree at  r e f e r e n c e and  be  thesis  I agree that  for extensive  p u r p o s e s may his  this  copying or  shall  not  per-  scholarly  Department o r  that  gain  for  freely  be  by publi-  allowed  ABSTRACT  Tim factors and mechanisms which consistently deliver newyly overwintered adults of the ambrosia "beetle •Prypodendron lineatura (Olivier) to specific host trees under specific conditions have been considered!. Studies and analyses of the behavioural patterns of the beetle im respect to light, host tree factors, and factors of the environment -were made i n recognition of the fact that preiimdasary research results demonstrated the predominant role that reactions to light played!, i n the behaviour of the beetle. The results of the studies showed that the beetles, before f l i g h t , were; strongly phototacstic at temperatures i n the range of 5° to 56°C. Bssitive photic response was inhibited i n am increasing percentage of i n d i viduals at temperatures above 56°.  At 58°0, positive response to light by  the beetles ceasedl to exists The non-flown beetles reacted; quickly to angular deviations of alignment im respect to a light source and turned, with almost equal readiness toward the light regardless of i t s atmgle. The beetles' responses to light may be classified as follows: ( l ) not inhibited, the beetles immediately, move toward the source of light; (2) i n i t i a l l y inhibited positive responsej (5) inhibited positive response, the beetles may or may not imic  t i a l l y inhibited but the general movement toward She light source i s not direct| (4) completely inhibited response, 'She beetles move with no apparent response to light* The photopositive response was found to mask: the other potential capabilities of the non-f lerwn beetles.  Exclusion of the photic stimulus  from £light-inexperiencedl beetles resulted i n response to host odour i n an odour f i e l d .  P l i g M eaqaerience was found to modify partially the simple  photic reaction of some individuals i n the absence of host odour, but the  majority of the "beetles' responses remained unchanged. The behaviour of Telodendron i s not s t r i c t l y stereotyped i a the sense that i t follows a definite pattern. While f l i g h t may be normal as & conditioning mechaaasmi preparatory to alighting and host finding, response to an "attractive * odour source and subsequent boring behaviour may be 1  exhibited, i n the absence of previous f l i g h t experience, under certain conditions.  iii  TABLE OF CONTENTS Bags ACMOWI^MBNTS  .. .. ..  1  LIST OF TABLES;  2  LIST OF ILLUSTRATIONS  5  INTRODUCTION  ..  5  MATERIALS AND METHODS .  :.  12  ....  12  The Experimental Insect  . . . . . . . . . . . . . . . .  1. General considerations  . . . . . . . . . . . . .  12  2. Source of the experimental supply of beetles and methods of handling and storage  . . . . . . . . . . . . . . . . .  5. Treatment of the beetles f o r testing . . . . . . . . . . Host Tree Factors H  14 .  15  . . . . . . . . . . . . . • • « . ....-••» .  16  General considerations . . . . . .  .....  ...•.••  2. Source of host wood and preparation for testing  .... .  17 19  5. Preparation of wood factors as stimuli to the responses ofi^the beetles • . • . • • . . . . . . . .  •.......  The Light Factors  20 21  1. General considerations . . . . . . • . . . . . . . . . . .  .  21  2. Description of the equipment used and methods of testing .  22  Accessory Factors . . . . . . o . . . . . . • • ••• • • • • « •• 1. Increasing temperature: i t s provision and use i n the  26  tests  . . . . . . . . . . . . »-••*• ... . . . . . • ••  2. Airstream: i t s provision' and use i n the tests  27  ......  50  3. Increasing atmospheric pressure: i t s provision and use i n the tests . • ... ••• •• ... . . » •• . . . . . . « • » « • • Methods of Observation . . . . . . . . . . . . . . . . . . . EXPERIMENTAL RESULTS  ;  51  ...  53  ...  56  TABLE QP CONTENTS (continued) Page 1. Responses to white light under normal laboratory conditions . . . . . . . . . . . . . . . . . . . . . . . . . .  . 36  2. Photic responses i n the presence of a i r current with or without wood odour • . .. . • • . • . . . . . • • • .. • • • • • .. 41 5. Photic responses i n the presence of "green" wood factors . . . » 44 4. Photic responses i n the presence of "attractive wood factors  ........  44  5. Responses to background black-and-white patterns . . . . . . .  49  6. Responses to white light under increasing temperature  ....  49  7. Responses of Trypodendron to various stimuli i n the dark . . .  57  DISCUSSION OP RESULTS  . . . . . . . . . . . . . . . . .  60  1. Photic behaviour i n Trypodendron: i t s ecological significance and i t s underlying mechanisms . . . . . . . . . . . . . . . . 2. The modifiers of phptic behaviour: their relation to hostfinding .... . o . . . . . .. . . . . . . . . . . . . . . » .  63  3. The behaviour of Trypodendron: i t s use i n bioassay techniques  72  CONCLUSIONS  .  LTTERATURE CITED .  60  74 78  ACMCWIMXJMENIS  To Dr. Kenneth Graham, professor of forest entomology, University of British Coumbia, f o r his invaluable advice, encouragement and kindness throughout the conduct of the experiments and preparation of this thesis, I am deeply indebted* To Dr. John A* Chapman of the Canada Department of Forestry, Forest Entomolpgy and Pathology Laboratory, Victoria, B. C , f o r his cooperation, courtesies and kindness i n furnishing biological specimens and i n offering helpful suggestions, I am deeply grateful. To the members of the Graduate Committee: Drs. J . <3F. H. Campbell, P. G. Haddock, W. S. Hoar, R. W. Wellwood, and D. J . Wort for their interest i n the conduct of the work on this thesis, grateful acknowledgments are extended. I also give my thanks to many individuals including Dr. A. Kozak, Hessrs. John Walters, J. M. Kinghorn, J . T. Welf, and P. Demko f o r giving help i n various ways, and to several institutions including the National Research Council of Canada, British Columbia Loggers Association, and the i  '•  Department of Zoology, University of British Columbia, for their assistance and permission to use laboratory equipment and space. Especially to the External Aid Office, Government of Canada, Ottawa, and the Forest Products Research Institute, Republic of the Philippines, for jointly granting a Colombo Plan Fellowship which permitted the pursuance of the work on this thesis, I extend my wholehearted thanks.  1  LIST OP TABLES Table l o . 1.  Page  Summary of responses of flight-inexperienced male and female Trypodendron to a horizontal beam of light under normal laboratory conditions  2.  ,.  57  Summary of responses of flight-experienced male and female Trypodendron to a horizontal beam of light under normal laboratory conditions  5.  40  Photic responses of adult Trypodendron under increasing temperature  4.  .  ....  . . . . . . . . . . . . .  56  Photic responses of adult Trypodendron as influenced by gravity and increasing temperature  2  . . . . . . . . . .  57  LIST OP ILIiU^TRATIONS  Figure Ho. 1. 2. 5.  Page  Trypodendron lineatum (Olivier) adult female beetle. Actual length 3 to 3.5 mm. (After Graham, 1963) . . . . . . .  13  A Reichert microscope illuminator "Lux FNI" operating through a variable resistor with an amperage indicator  25  . .  Diagram illustrating plan of view of the i n i t i a l starting points or angular displacements of the beetle Trypodendron i n tests f o r i t s responses to a horizontal beam of white light . . . . . •  25  Apparatus used for testing responses of Trypodendron to light i n a temperature gradient  28  5.  Apparatus and set-up for testing photic responses of Trypodendron i n relation to gravity and increasing temperature .  29 A  6.  Apparatus for testing photic responses of Trypodendron under increased atmospheric pressure ......  55 A  Scheme of programme of experiments on the photic responses of Trypodendron lineatum (Olivier) i n relation to various host wood factors and conditions of the environment .......  55  A to H. Representative paths of response to a horizontal beam of light by newly overwintered adult females of Trypodendron lineatum (Oliv.) . . . . . . . . . . . . . . .  58  A to H. Representative paths of response to a horizontal beam of light by newly overwintered adult females of Trypodendron lineatum (Olivier),. . . . . . . . . . . . . .  39  A to D. Representative paths of response to an overhead source of light by newly overwintered adults of Trypodendron lineatum (Oliv.) . . . . . . . . . . .  42  A to D. Representative paths of flight-inexperienced and flight-experienced adult Trypodendron i n response to a gentle stream of a i r without odour or with attractive host wood odour . . . . . . . . . . . . . . . . . . . . . . . .  45  A to D. Representative paths of responses to light and to an airstream with or without attractive host wood odour by flight-experienced as well as flight-inexperienced adults of Trypodendron placed on a perforated area on a sheet of paper above a piece of "green" wood . . . . . . . . . . . . . . . . . . .  45  4.  7.  8.  9.  10.  11.  12.  5  LIST OF ILLUSTRATIONS (continued) Figure Fo. 13.  Page  A to D. Representative paths of responses to light and to an airstream with or without attractive host wood odour "by flight-inexperienced as well as by f l i g h t experienced adults of Trypodendron i n direct contact with a piece of green" wood M  14.  15.  16.  17«  18.  46  A and B. Representative paths of responses to light and to an attractive piece of wood under perforated area on sheet of paper by flight-inexperienced and f l i g h t experienced Trypodendron beetles . . . . . . . . . . . . . .  50  A and B. Types of response to light and to an airstream without attractive wood odour by flight-inexperienced and flight-experienced Trypodendron beetles on a perforated sheet of paper above attractive host wood. . . . .  51  Representative paths of response to light by f l i g h t inexperienced and f l i g h t -experienced adult Trvjspdendron beetle placed on a perforated sheet of paper above attractive host wood and subjected to a gentle stream of a i r with attractive wood odour . . . . . . . . . . . . .  52  A and B. Representative paths of response to light by the flight-inexperienced o r flight-experienced Trypodendron beetle i n contact with a piece of attractive host wood .  55  A and B. Representative paths of response of f l i g h t inexperienced and of flight-experienced adult Trypodendron beetle to light and to a stream of a i r with attractive wood odour. . . . . . . . . . . . a . . . . . . . . . . . .  54  19.  Representative paths of response of the flight-experienced Trypodendron beetle placed i n contact with a piece of attractive wood i n relation to light i n the presence of an a i r stream with or without attractive host wood odour. . . . 55  20.  Effect of increasing temperature on the photic, responses of Trypodendron lineatum (Olivier)-.. . . . . . . . . . .  58  Comparison of effects of gravity and increasing temperature on the photic responses of Trypodendron lineatum (Olivier)  58  21.  4  IMrRQDUCREIQN  Among the general problems concerning ambrosia, beetles are those which pertain to their host tree relations.  More specifically i s the ques-  tion as to the factors and meahaiaifflms which consistently deliver these insects to host trees of specific kinds and conditions. The question i s prompted by the fact that ambrosia beetles show remarkable a b i l i t y i n discovering f e l l e d , wir^tbrown, or dying trees im a forest, or logs i n water storage, "selecting" them as to botanical identity and state of morbidity i n the sequence of changes between l i f e and death.  They are even able to  detect these special requirements despite heavy coverage of the log surface with substances objectionable or confusing to human olfactory sensation, such as creosote and kerosene, or despite a residue of the insecticide lindane which ultimately Trills those beetles as. they crawl over the log surface. Two associated problems are posed by the foregoing observations. One concerns the identity of the intrinsic and extrinsic factors and the behavioural patterns and mechanisms involved!, i n the process of host discovery and discrimination.  The other concerns the nature of the facttes i n a  log and the mechanisms of their origin which account for the differential attack by these beetles on logs of different kinds and conditions. These problems are of both academic and practical importance. Considerations of the general problems, i n turn, pose subsidiary questions.  Does attack involve random trial-and-error sampling by the  beetles, or does the insect detect i t s host from a remote point?  Of the  various conceivable differences between l i v i n g and dying trees., which of them should be capable of providing essential cues for the beetles? If 5  6 detection i s from remote points, •which of the possible phenomena, i n a dying tree may act at a distance, and which of the psa-mi.ac  conceivable senses;  i n insects may take part i n remote detection? If odours play an important role, as may be inferred from certain f i e l d studies, (Chapman, 1962, 1965), are they absent from the healthy l i v i n g tree, or merely occluded within the cells u n t i l mechanical alterations, such as permeability or hydrostatic pressure changes, release them s&en the tree begins to die, or does the change also involve the disappearance of chemical repellents?  I f attractants  are normally absent, why do they not develop i n the l i v i n g tree, and why do they form as i t begins to die? I f a chemoal process, i s iwolveii, does i t involve simple oxidation, simple cleavage, condensation, polymerization, molecular rearrangement, or abnormal metabolism?  If abnormal metabolism i s  involved, how? may normal and/or abnormal metabolism be a r t i f i c i a l l y modified!, to accelerate or retard the formation of chemical attractants?  i f chemical  attractants are formed, what are their group or specific chemical natures? Can their attractancy be obscured by other substances presented simultaneously with them to the insects?. The foregoing questions are of a factual and observational nature, some having practical implications . There i s to be considered also the conceptual aspect which pertains to the relationships of ambrosia beetle behaviour to the general theory of animal behaviour.  Kennedy (1956, 1958)  refers to three types of hypothesis concerning the nature of instinctive behaviour.  One i s the simple physiological one such as Loeb favoured,  according to which reflex and instinctive action do not differ i n prineijftLe and changes, of behaviour pattern are due primarily to changes, i n the reflex thresholds brought about by changes i n the state of receptors and effectors.  7  A second hypothesis, "based on the work of reflex physiologists, notably Sherrington, also recognizes no difference of principle between reflex and instinctive action but attributes changes of threshold primarily to the integrative activity of the central nervous system. A third hypothesis, advanced by the modem ethologists, draws a distinction of principle between reflex and instinctive action, the latter depending on an internal drive-generating mechanism which, even -vftien triggered by an external stimulus, has nothing i n common with reflex: mechanisms. The general study comprises several largely distinct but not entirely mutually exclusive tasks.  These consist of analysis of behaviour  i n the insect, experimental modification of living and dying trees, and chemical and histochemical analysis of changes i n chemical precursors and products of trees as they gradually die.  The objective of the present  phase of the undertaking i s to investigate the behaviour of the insect, particularly i n relation to the circumstances affecting i t s response to host tree factors. The present investigations pertain to the ambrosia beetle species Trypodendron lineatum (Olivier) which has been an object of much concern and research i n recent years.  Earlier studies on this insect (Graham! and  Werner, 1956) revealed that the reproductively mature beetles, freshly removed from their overwintering quarters i n spring, are entirely dominated by a strong photopositive response.  In the presence of light, they do not  bore into the kind of wood that i s normally being attacked by non-captive individuals i n the f i e l d ,  i n darkness, they bore readily into attractive  wood, or into non-attractive wood to which gas-distilled attractive wood are applied.  extracts of  This contrasts with events i n the f i e l d  8  where attack takes place i n broad daylight. Subsequent observations (Graham, 1959) showed that the a b i l i t y of the beetles to bore into wood i n daylight depends on their f i r s t having a period of f l i g h t .  This appears  to simulate one stage i n the natural sequence of events i n the f i e l d . Balfour and Iteramonov (1962) contend- that f l i g h t i s not absolutely necessary.  They found that under severe confinement, a small percentage of  beetles w i l l attack wood while exposed to light without hawing been preconditioned by f l i g h t .  Further experience by Grahamt (1965), however,  sustains the original basic conclusion that the i n i t i a l l y strong photopositive response i n overwintered adults of Trypodendron i s a major obstacle to their boring-in activity u n t i l they have experienced f l i g h t . It i s conceivable, however, that Balfour and J&ramonov's observations signify that i n certain populations or i n certain samples of beetles from themi different thresholds of responsiveness to host factors already exist among the various individuals and that the threshold i s lowered f o r a l l individuals by the f l i g h t experience.  I t should be noted that i n their  caution of precluding the possibility of their beetles having had f l i g h t experience, Balfour and Paramonov used specimens which had been extracted a r t i f i c i a l l y from brood logs and stored u n t i l spring. Thereby they denied the beetles the normal prehibernation f l i g h t . Further investigations (Graham, 1961) indicated the importance of air-swallowing as a mechanism by which photic reactions are subdued to a point where responsiveness'to host factors i s released.  Mnirmmn periods of  f l i g h t f o r this purpose were, however, not ascertained. The discoveries to this point l e f t various details of behaviour i n Trypodendron untouched.  9 No evidence exists to indicate that T. linea-tum host tree or log "by a random, trial-and-error process.  discovers i t s  During the attac-  king phase of i t s l i f e , i t appears never to settle on hosts other than those of a particular species i n a particularrstate between the l i v i n g and the dead. These are the logs into which they w i l l bore to establish their broods. I t i s thus evident that the mechanism of detection operates over an appreciable distance. Entomologists are familiar with three forms of perception which enable insects to receive ^information at a distance, namely vision, audition, and olfaction.  Certain evidence exists also for a sense of perception of  bioelectric f i e l d s (tew, 1961, 1962) even though no structure f o r their perception i s known. Of the various properties of plants which emit information that i s detectable at a distance, two classes of factors are well-known. One i s odour j the other i s of a visual nature, v i z . contrast, form, and colour.  Perhaps bioelectric f i e l d s should be considered as being a possible  source of information to insects (Haw, 1961, 1962). As to the significance of voltage gradients (Parr, 1945) or bioelectric oscillations (Scott, 1962) as a source of signals f o r insects, nothing i s known. It i s not entirely inconceivable that movement of fluids and gases i n a tree may be accompanied by subsonic or supersonic propagations of low intensity, but experimental evidence i s lacking. The fact that Trypodendron, during the attacking phase i n i t s l i f e cycle, appears not to settle on the "wrong" kind of logs or trees indicates that visual cues are not primarily or predominantly involved i n host discovery.  This i s not to deny that sight i s probably involved i n their guidance  mechanism. Oh the other hand, the important role of odour i n the guidance of  I D  insects i s well-known. Furthermore, hidden log experiments i n the f i e l d (Chapman, 1962, 1965) have demonstrated convincingly that odour must be a prime factor i n host discovery by Trypodendron. With this evidence, i t appears prudent to examine as f a r as possible the role of odours before testing for the operation of factors whose importance or existence f o r insects i s uncertain. The foregoing observations on T. lineatum accordingly indicated, the i n i t i a l dominance of the photic response and the release of a chemotactic response by exclusion of light, or by f l i g h t experience, the latter operating by inducing the swallowing of a i r . It was also evident that an olfactory guidance mechanism i s involved, and volatile chemicals extracted from attractive wood are capable of inducing attack (boring-in) on otherwise non-attractive wood. An olfactory response to host factors was suggested, by their tendency for an unstable aggregation about odour sources from attractive wood provided that light i s excluded and that the a i r i n the immediate surrounding of the beetles was not excessively dry (Graham and Werner, 1955) • The knowledge about Trypodendron now raised as many questions as i t had answered. I t was not known how long a period of f l i g h t i s required for the appearance of a change i n the response to host factors i n the presence or absence of host factors. Heither was i t known whether the effect of f l i g h t on the photic and host factor responses i s all-or-none, or whether i t involves a progressive change of thresholds.  It was not known  either whether the beetles could orientate to a stationary odour gradient, or to an airstream carrying odour. The laboratory experiments implicating odour i n behavioural effects were at this point quite meagre. By the same token, there were no satisfactory c r i t e r i a by which olfactory responses  11 could "be detected, assessed, or clearly segregated from the other responses which are incorporated into the more complex: reaction of boring into wood. The objectives of the present investigations were to explore factors and mechanisms of the orientation behaviour of Trypodendron lineatum (Olivier) during that stage i n i t s l i f e when i t searches out, selects, and attacks logs. This period i s i n the overwintered reproductively mature adults.  The immediate study i s confined to pedestrian beetles because i t  appeared that much of their behaviour could best be gained under this circumstance.  The study of photic reactions i s here limited to the photopic (light  adapted) state. Special attention i s directed at photic reactions and factors which modify these.  MATflRTATfi AND METHODS  Trypodendron lineatum (Olivier) (Fig* l ) of the family Scolytida© was the species of ambrosia beetle used i n these studies. 1. General considerations.The species T. lineatum i s , of a l l the thousand or more world  ;  species of ambrosia beetles, one of the most suitable f o r study. I t occurs over an extremely wide geographic range, being found i n the temperate coniferous forestcof Europe, Asia, and North America (Hadorn, 1955; Chamberlin, \  1939; Novak, 1963; Bletchly and White, 1962).  A considerable body of l i t e -  rature i s available as background information on i t s general habits, biology, physiology, and ecology (Hadom, 1955; Chamber l i n , 1959; Chapman, 1955, 1958, 1962, 1965; Chapman and Dyer, 1960; Chapman and Kinghorn, 1961; Dyer and Chapman, 1965; Graham, 1959, 1961; Graham and Werner, 1959; Nijholt and Chapman, 1964; Novak, 1965a, 1963b; Prebble and Graham, 1957; Radinsky and Daterman, 1964a, 1964b).  Its habit of overwintering during a period of i t s  adult l i f e i n the forest l i t t e r , duff, or under flakes of bark on trees  adja-  cent to logging or logged-over areas (Hadorn, 1933; Novak, 1965; Chapman, 1960; Ghapmajn and Kinghorn, 1961; Dyer, 1962, 1965) permits collection of biologically uniform material i n sufficient quantity for convenient experimentation i n the laboratory.  This contrasts with most other ambrosia beetles  which are f a r less synchronous and do not accumulate i n an intermediate storage medium,but search new logs almost directly following emergence from the brood log which nurtured them. Trypodendron adults are amenable to prolonged storage under refrigeration without showing marked loss of vigour or a b i l i t y to f l y or walk provided they are not exposed to desiccation of 12  13  Fig, 1 . Trypodendron lineatum (Olivier) adult female "beetle. Actual length 5 to 3.5 mm., (After Graham, 1965)  14 more than 25 per cent of their body weight (Nijholt and Chapman, 1964). The visible differences between the sexes render them easy to define f o r the purpose of the experiments. The versatility of Trypodendron i n accepting a wide range of genera of coniferous trees offers considerable freedom of choice i n the kinds of wood which may satisfy certain needs of experimental convenience.  The same diversity i n respect to acceptable host species may provide  increased opportunities for discovering the essential chemical attractants by correlative evidence. 2. Source of experimental supply of beetles and methods, of handling and storajjey'The source of the beetles was i n the Gowichan Lake d i s t r i c t of Vancouver Island, British Columbia.  The time of collection was i n late  March and early April, 1964, just prior to the beetles* normal emergence as. reproductively active adults from their overwintering quarters. Collections were obtained  within a. zone of about 100 meters inside the margins of  standing forest adjacent to areas i n which logging had been i n progress about 18 months previously. Here the brood of new beetles, generated during the season preceding the collection, occurs i n the duff layer near the base of standing trees, and under loose flakes of bark on the lower stem of very old Douglas f i r trees. Old adults may occasionally be found among the population of overwintering new adults at a proportion of about 1 to 50 per cent (Chapman and Mijholt, 1965). Bark flakes and forest duff containing the beetles were freed of coarse material and stored i n plastic bags i n a refrigerator at a temperature of about 0 to 5°C.  Whenever beetles were required f o r the experiments, they  were obtained by spreading the beetle-containing medium, a couple of handfuls  15 at a time, i n a shallow pan floating on 'cater at a temperature of about 50°G. As the beetles became activated, they were transferred to amai^ jars containing moist crumpled paper towelling or bits of moist moss to prevent loss of body moisture and to minimize mutual contact among the beetles, as otherwise the beetles bite o f f each other's front t a r s i .  Specimens thus mutilated  are hardly able to walk normally and become useless f o r the purposes of the experiment.  Care also had to be exercised i n intercepting the beetles before  they could take off i n flight as i t i s known that this factor modifies their responses to light i n the presence of odour from attractive wood (Graham, 1961) and to attractive odour i n the presence of light. 3. Treatment of the beetles f o r testing.The supply of beetles used i n the experiments was segregated* as to sexes. They were placed i n jars with moist paper or moss. To prevent the beetles from becoming very active i n the presence of light at room temperature, the jars containing them were kept i n a thermos jug containing ice. Beetles were removed from the jars as needed i n the experiments. The beetles were tested for their photic behaviour immediately after removal from cold storage and without allowing them to experience f l i g h t . Later, the same beetles were given a period of captive f l i g h t by means of a procedure described by Chapman (1956). This was done for the purpose of studying details of the effect of f l i g h t experience on photic orientation as well as observing the time patterns of flight activity per se.  Each  beetle was glued by i t s pronotum to the underside of the t i p of .^iicardboardinsect-mounting point.  The beetle was affixed i n such a way that i t was  horizontal and that i t s wings were not obstructed i n motion by the paper point or any glue. I t was also noted that interference of glue with  anten-  16 mal movement suppressed a l l effort of f l i g h t .  Four or five beetles i n d i v i -  dually affixed to separate points, each set on an entomological pin, were observed concurrently.  At every one minute interval, the flight activity  of each beetle was observed and recorded horizontally across graph paper ruled at ten lines per inch. Positive activity on each beetle was indicated by an x" sign, while inactivity was represented by a blank square. Total tt  f l i g h t as well as periodicity of intermittent f l i g h t were thus known. The beetles were kept under these flight-testing conditions for various periods of time, from 5 minutes to 6 hours. To prevent possible loss of body moisture during the f l i g h t period and exposure to light, the piece of balsa wood to which the pins supporting the beetles were stuck was kept i n a shallow pan of water. After the prescribed period of f l i g h t , the beetles were removed from the card points to their respective vials, care being exercised so as not to cause injury to the beetles, and again tested for photic response, one at a time, or for responses to some other stimuli concurrently with the light factor. Host Tree Factors Like the beetles i n being important as both objects and instruaents i n the study of behaviour i s the host tree. The wood ofcthe:hbstitree i s eventually to be investigated for products of biochemical changes, factors and mechanisms which are involved i n rendering the wood attractive to ambrosia beetles.  I t i s noteworthy that the attractive condition for the ambrosia  beetles develops develops i n a tree from the effects of injuries and exposure after a certain period of time. Before the attractant factors can be clearly interpreted preparatory to isolation and evaluation, i t i s necessary to .  elucidate the accessory conditions required to induce aa effective response of the insect to the host.  For this purpose, portions of known attractive  and non-attractive host materials were provided as reference standards of host factors. 1. General considerations. The recorded host trees of Trypodendron are Douglas f i r (Pseudotsuga menziesii /SfLrbJ? Franco), amabilis f i r (Abies amabilis Jjtovygjfeorb.), grand f i r (A. grandis ^Douglj7 Forb.), western hemlock (Tsuga. heterophylla Sarg.), spruce (Picea spp.), pine (Pinus spp.) i n British Columbia (Erebble and Graham, 1957) ; noble f i r (Abies procera), larch (igrix leptolepis)  t  spruces (Picea abies and P. sitchensis), pines (Pinus sylvestris  and P. radiata) i n Scotland (Bletchly and White, 1962), and several species of spruce i n Europe (Novak, 1965b). Host tree material of Trypodendron provides several different kinds of stimuli which may affect this insect i n various ways. These include the tactile stimulus arising from contact with solid object.  The  solid surfaces may offer various topographic features varying from smooth plaques and deep narrow fissures as exist i n bark texture to relatively f l a t and coarse surface as exists on the cut or sawn ends of logs.  The  colour may also vary considerably but i t s stimulating character i s unknown. Odour i s perhaps the most important stimulus to consider because mostainsects react to i t i n a very remarkable manner (Dadd, 1963; Dethier, 1965; Buddenbrock, 1958; Kennedy and Booth, 1959a, 1959b, 1960; Roedear, 1965; (Sara and Vite, 1962).  En Trypodendron^ the odour of a suitable host tree appears  to be a guiding factor (Chapman, 1965). Taste i s a factor to which most insects have a low threshold of sensitivity (Dethier, 1965) and which may  18 affect the reactions of the beetles as they begin to chew into wood. Another conceivable stimulating factor i s the visual form or mass of the host (Dethier, 1957) but i t s influence on Trypodendron i s not known. As i t i s the purpose of the study to deal with factors involved i n the attraction of the beetles to their host, material was chosen especially to provide a source of the odour stimulus.  Accordingly, features of bark  topography and colour and the property of taste played no part i n the selection of the speoific host for the preparation of the samples. There were other considerations i n the choice of wood. One i s the choice of tree species among the potential or known host species of Trypodendron. Fbr experimental convenience, certain preferences had to be made, since i n the particular area where the experimental beetles were obtained, western hemlock and Douglas f i r are not only the most commonly available trees but are also usually the most heavily attacked by Trypodendron (Graham and Werner, 1956).  Of these two trees, Douglas f i r i s noteworthy  for i t s white sapwood region which becomes attacked by the beetles and i s easily differentiated from the reddish region which i s immune to attack. Also, Douglas f i r wood had been a subject of chemical investigation f o r i t s attractant properties (Graham and Werner, 1956). Douglas f i r , however, possesses a limited sapwood layer which prohibits obtaining convenient siae of tranverse slices for testing attack response; of the beetles and, more important, appears to change from the non-attrative "green" condition to the attractive "ripe" condition i n a shorter time than does hemlock. This instability i s disadvantageous where alteration of host material condition during the course of the experiment i s undesirable.  For this reason,  western hemlock appeared preferable as a source of wood i n studies of  19 attack responses and as a source of odour i n studies of orientation to light and a i r flow. Another consideration i n the choice of wood concerns i t s state of attractiveness.  The state of attractiveness can be measured only by the  response of the beetles.  The chemical identity of the attractants i s not yet  known. In so f a r as attractiveness to the beetles i s concerned, however, a host tree exists i n several conditions ranging from a '"green'* state as exists i n the wood of a newHy f e l l e d tree to a "ripe" state which i s highly favoured by the beetles and to a "spent" state i n which the attraotant factors are no longer present as i n logs, wood, or finished dry lumber. The attractive or "ripe" state develops during winter i n the sapwood of the unconverted host trees f e l l e d during autumn and winter.  Spring-felled  trees with tops retained, or cut only into long log lengths remain unattrad* tive to the beetles through the spring f l i g h t period of Trypodendron but become highly attractive i f cut into short log sections at the time of f e l l i n g (Johnson, 1964). 2. Source of host wood and preparation f o r testing. The "ripe" and the "green" wood materials came from the same local i t y as the experimental beetles.  The attractive state of the wood samples  was assured by taking them fromi polyethylene-sheet-covered  portions of logs  of host trees f e l l e d i n early winter and allowed to remain i n the woods until attacks occurred on the uncovered portions.  These "ripe" samples as well as  "green" samples from spring-felled host trees were stored as thick slabs i n plastic bags i n a freezer at about -17.8°C (0°F). Samples of both "ripe" and green" wood for testing attack rt  responses of the beetles were prepared by debarking the frozen slabs,  20 squaring the edges, and planing the surfaces with a woodworking "jointer" machine. The shavings obtained from the planing operation were saved i n plastic bags and stored i n the freezer. 5. Presentation of wood factors as stimuli to the beetles' responses The method used for evaluating the olfactory response consisted of testing for the retention of the beetles at an odour source while they were subjected to the potential attraction of a beam of horizontal light or a broad f i e l d of light whose source  i s overhead. A sheet of paper, finely  perforated with pinholes at the center, was placed over a small section of either "ripe" or "green" wood, about 5.0 cm. by 7.0 cm. by 1.5 cm., as desired.  The beetles were placed individually on the perforated area to  examine the ability and behaviour of the beetles i n orienting to a gradient of odour emanating from the wood beneath the paper without involving a stream of a i r . Another condition under this series of tests ;consisted of associating wood with a stream of a i r alone or with "ripe" wood odour borne by a stream of a i r . The purpose of the test was to determine the possible occurrence of an anemotactic response prompted by the host odour. This would concern an alternative mechanism to the odour-gradient theory of host finding. In another series of tests, the. beetles were allowed physical contact with the piece of either "ripe" or "green" wood. This series would provide not only thigmotactic behaviour responses on physical contact with the piece of wood but also chemotactic behaviour responses as a result of tarsal contact and/or oral tasting of the host wood. In addition, the effect of contact with the source of the attractive wood odour may provide  a different response. The jtfigot Factors In i t s most comprehensive aspects, the photic behaviour of an insect would be concerned with the directional changes and time patterns of i t s orientation reactions under diverse conditions of a photic environment. Light may be varied as to intensity level, specific wavelength, wavelength balance i n mixed colours, degree and plane of polarization, discreteness or diffuseness, and angle and plane of incidence relative to the axis of the insect. "Various contrast and colour patterns, both stationary and moving, i n the visual f i e l d may influence the responses (Reiohardt, 196l).  A l l of  these are possible elements and variables to which Trypodendron i s subjected i n i t s natural environment.  In addition, the insect may be expected to  respond differently i n the dark-adapted and light-adapt edl states as demonstrated by Raymont (1959) with the beetle Dineutes.  The present studies  employed mainly a heat-filtered, unidirectional white light of constant intensity and colour temperature, projected i n a beam toward the beetles and a broad f i e l d of overhead light provided by ceiling fluorescent lamps. 1. General considerations.Light i s an important factor of the environment to which insects react either positively or negatively under certain conditions.  Light i s  defined as that portion of the electro-magnetic spectrum ranging i n wavelength from about 200 to 10,000 m/u or about 2000 to 100,000 %l  The light  visible to human eyes ranges from 4000 to 7500 %. while that to a bee's eyes ranges from 3000 to 6500 A (Carthy, 1965).  In terms of colour which the  different wavelengths represent to human eyes, the bee's eyes can d i s t i n guish colour i n the ultraviolet range and not i n the f a r red range of the  spectrum. As a token stimulus, light i s "wsry effective I n that i t s reflective and absorptive characteristics provide insects some kind of information about their environment. Changes i n light intensity associated with shadows of moving objects notify the insects of the presence of prey or enemy. Because infrared wavelengths usually accompany visible light under aerial conditions, brighter illumination means a warmer, drier environment, and a lower illumination may mean a cooler, damper one (Brown and Erosser, 1962) • 2. Description of the equipment used and methods of testing.The source of white light was a Reichert microscope illuminator "Lux FNI" (Pig. 2) operating through a variable resistor with an amperage indicator.  Its normal rating was 50 watts at 6 volts and 5 amperes. This  equipment gave control over light i n respect to focus, aperture, intensity, and to a certain extent, colour temperature.  Because the wavelength balance  (colour temperature) of light from a tungsten filament changes with voltage of input current, a fixed setting of the rheostat was adopted for an input of 4.0 amperes. The incident light to which the beetles were exposed was measured by a "Ehotovolt" photometer model 200 M as ranging from 25 to 50 footcandles.  Colour temperature was judged to be similar to that of a 40-  watt incandescent bulb operating at normal voltage, the value of which i s rated at 2760° Kelvin.  To insure that the responses to the horizontal  beam of light were purely photic and not thermal, a heat f i l t e r from a Bausch and Lomb projector was interposed. The overhead source  of light was provided by four "General Elec-  t r i c " cool-white F40 GW fluorescent ceiling lamps at a distance of about two metres above the experimental table. The incident light furnished by these lamps ranged from 50 to 60 footcandles as measured by the  ;. ;  Fig. 2. A Reichert microscope illximinator "Lux SKI" operating through a variable resistor with an amperage indicator. It was used as the source of a horizontal beam of white light.  A Bausch and Lomb heat f i l t e r i s shown  in front of the illuminator.  24 "Ehotovolt" photometer. The simple photio reactions were tested by placing the beetles, one at a time, at a central point oh a sheet of white writing paper.  A  narrow beam of heat-filtered light, as defined earlier, was projected horizontally across the surface of the paper. The beetle, i t s sex rioted, was aligned with the axis of the beam. As the beetle was allowed to walk, a pencil line was traced behind i t u n t i l i t reached the edge of the paper, whereupon i t was returned to the starting point,  lax some tests, the o  beetles were aligned i n eight different directions, 45 apart, i n respect to the Light source. were tried.  In other tests, only four directions at 90° intervals  These starting points are illustrated i n F i g . 5.  The syste-  matic testing of angular displacement was provided i n recognition of the fact that certain insects react at different rates to different axial displacements relative to the light sour<5o,(Euddenbrock,:,1958; Fraenkel and Gunn, 1961).  Besides the systematic tests which began with a fixed  starting direction, other tests with different i n i t i a l directions of alignment were tried i n order to examine f o r possible adaptation of the insect during successive t r i a l s .  After the beetles were each exposed to a h o r i -  zontal beam of light, they were tested for their responses to a broad f i e l d of light.  Essentially the same positions on the white sheet of  paper were used i n aligning the beetles. The photic reactions were tested i n the presence of other factors such as wood odours, a i r currents, increasing temperature, gravity, and atmospheric pressure.  The beetles included both flight-experienced and  flight-inexperienced individuals. Previous observations indicated that the individual beetles  25  T  Direction of light  1  V 5 Fig. 3. Diagram illustrating plan of view of the i n i t i a l starting points or angular displacements of the beetle Trypodendron i n tests f o r i t s responses to white light.  26 walked toward a point source of a horizontal team of light and began attempts to f l y when light was present i n a l l directions as provided by the ceiling lamps. These observations led to undertaking a test to determine the responses of the beetles to light coming from below the horizontal plane of sight of the beetles. For this purpose, the beetles were i n d i vidually placed on a sheet of transparent glass below which a light was placed.  Following this test, a combination of light coming from above  and below the beetle was tested to determine the responses of the beetles. The orientation behaviour and responses to host wood factors ware also studied i n the absence of light.  The beetles were individually placed  i n a. cardboard box, about 50 cm. by 45 cm. by 15 cm., painted black inside. The beetles were placed on a predetermined position on a piece of paper inside the box which at times contained either an attractive or a ""green* 1  piece of wood as a particular test demanded; the box was afterwards covered for a period of about five minutes; then i t was opened to determine the position of the beetles. Another condition of testing consisted of passing wood odour through a hole i n one side of the box. Accessory Factors The behaviour of insects under natural conditions i s often stereotyped, described i n terms of inborn pattern of behaviour commonly known as. instincts (Dethier and Stellar, 1964; Scott., 1963; Fraenkel and Gunn, 1961). Inborn reflexes, and reflexes "conditioned" by previous experience  may  occur but are often masked by inhibitors and integrated i n such a way that they serve the needs and purposes of the insect as a whole. According to Wigglesworth (1953), "stimuli which the insect can learn to associate wiihi the presence of food, or with the location of i t s nest, are judged to be  perceptible.  Such experiments, of course, need the greatest care i n their  interpretation; for the insect may be guided by some other stimulus that has been overlooked by the experimenter; indeed, i n the course of a single experiment, i t may cease to be oriented by one stimulus and come to depend upon another; and there are many who hold that the whole perceptual experience of the organism i s integrated, as i t were, into a pattern, and not to the isolated stimuli of which i t i s composed.'* While certain aspects of specific responses, or the aggregate behaviour of a species may be recognized as being peculiar to i t i n various ways, the component responses to internal (physiological) cues and external stimuli may show considerable f l e x i b i l i t y as a result of modifying accessory factors.  These factors have to be considered.  1. Increasing temperature; i t s provision and use i n the test3.^Earlier observations (Graham, 1959) indicated that photic reversal of Trypodendron occurred when the temperature was i n the region of 55° to 58°C but i t was desired to evaluate the effect i n a more quantitative way. Several methods of test were employed.  The f i r s t method made use of a glass  tube, 2.0 cm. i n diameter and 85 cm. i n length, stoppered at the ends, placed i n a temperature gradient apparatus (Pig. 4).  The gradient appa-  rat us consisted of a long shallow copper trough, to the under surface of which were soldered two lengths of copper tubing, one at either end of the trough and not intercommunicating.  The tubing was folded i n a zig-zag  manner to give maximum contact with the trough. through one tube and cold through the other.  Hot water could be passed  Flow of the hot and cold water  respectively was regulated to produce a temperature gradient from 15°C at one end and 40°0 at the other.  The glass tube into which the beetles  28  Fig. 4. Apparatus used for testing responses to light i n a temperature gradient.  29 were placed was coated with a transparent red varnish, except for annular clear zones of about 2.0 cm. i n width spaced about 15.0 cm. apart. The red zones were provided to create conditions which would constitute darkness to the insects, yet would enable the observer to see through. A strip of moist tissue paper was placed inside the glass tube to provide a crawling surface for the beetles.  The beetles were put i n groups of five, sexes  noted, at the colder end of the tube; then, stoppered. A beam of white light was projected successively into each clear zone f o r five minutes at a time beginning at the colder end.  The number of beetles aggregating at the  lighted zone was recorded i n relation to the temperature at the particular point i n the gradient. Another arrangement of apparatus was designed to relate the effect of temperature and of gravity to the photic responses of the beetle. This consisted of a water bath apparatus and a wide-mouth glass jar whose outer surface was painted f l a t black, except for two clear areas, each about three centimeters square.  One of these clear areas was about two  centimeters below the rim of the mouth of the jar. The other area was at the opposite side, near the base.  A thermometer was f i t t e d through the  black rubber stopper and strips of moistened tissue paper, about 2.0 cm. i n width and 11.0 cm. i n length, were attached to the bottom surface of the rubber stopper so that when the jar. was stoppered, the t i p of the thermometer was halfway down the jar and the strips of paper touched the interior bottom surface.  The apparatus i s shown i n F i g . 5.  Groups of five beetles, sexes noted, were put inside the j a r . After being stoppered, the jar was immersed i n a water bath. The water bath apparatus consisted of a cylindrical glass vessel containing warm  29 A  Fig. 5. Apparatus and set-up for testing responses of Trypodendron in relation to gravity and increasing temperature.  50 water whose temperature was varied from 15° to 40°G. A beam of white light was projected into the upper clear window so that the beetles had to climb or crawl up the paper strips (against gravity) to react to light.  Once the  number of the beetles responding positively to light had been recorded, the beam of white light was moved to the lower window. The beetles' movement would then be toward the force of gravity as they responded positively to light.  The test was performed for every five-degree rise i n temperature  u n t i l 40°©. 2. Airstream with or without wood odour; i t s provision and use i n the teats.Anemotaxis i s the term applied to reactions or orientation i n an a i r current (Praenkel and Gunn, 1961). Many species of insects, on taking to f l i g h t , head into the wind. Drosophila f l i e s are known to walk and orientate very accurately into a wind containing the smell of mashed f r u i t . In Trypodendron beetles, the typical and characteristic f l i g h t orientation i s against the wind (Chapman, 1962). Praenkel and Gunn (1961) state that i t i s probable that many olfactory reactions are possible only with the a i r of a i r currents and that the means of reaching the source of odour i s to go against the wind or a i r current.  To test for the anemotactic  and anemo-  olfactory effects on the photic reaction of the beetles, a gentle stream of a i r flowing at 0.5 meter per second (as measured by a "Wallac-Thermex GGA2C" thermo-anemometer), f i r s t without bearing wood odour, and then with odour i n i t , was directed to the beetles, i t s sex noted, as i t was being tested for i t s reaction to light.  The odour was provided by passing the  airstream through a bottle containing either a mass of shavings from attractive wood or sawdust from unattractive "green" wood or various combinations of attractive shavings and "green" sawdust respectively.  51 Another teat concerned the effect of a i r streaming i n an odourfilled  environment. The purpose was to test for the operation of aneap-  tactic response that i s prompted by the host odour. Accordingly, the beetles were brought into an odour f i e l d by placing them on perforated paper over attractive wood and exposing them to a stream of either non-odorous or wood-odour-carrying a i r flowing i n the direction of the light source. TJests of response to non-odorous and odour-bearing airstreams ware also made with beetles placed inside a dark box.  Non-flown as well as flown  (flight-experienced) beetles were tested. 5. Increasing atmospheric pressure: i t s provision and use i n the tests.Experiments were devised to test for one of the possible mechanisms by which the a i r bubble i n the ventriculus of the flight-experienced beetles (Graham, 1961) may function i n the modification of the photic response.  One  possibility i s that the gas bubble functions by crowding the internal space, thereby creating haemostatic pressure which i n turn relays the effect as a ;  signal to a pressure receptor centre.  Another possibility i s that a signal  i s received more directly by stretch receptors i n the wall of the ventriculus i n which the bubble occurs.  A third possibility i s that the crowding  of internal space may stimulate stretch receptors i n the body wall.  In the  absence of morphological evidence for stretch or pressure receptors i n Trypodendron, the question must be approached experimentally. In experiments with spruce budworm larvae, Wellington (1948) demonstrated that photic reversal i n f l a c c i d individuals could be brought about by such turgor-causing factors as feeding, injection of f l u i d into the gut or into the haemolymph, or the imposition of external pressure by means of ligaturing.  It would be of both academic and practical experimental  interest to know whether the olfactory and other responses of Trypodendron can be studied while keeping the insect under pressure, i n l i e u of the otherwise necessary conditioning flight (Graham, 1961). It was assumed that i f pressure, and not: stretohv i s the mechanism involved i n the change of photic response of Trypodendron, i t s effect could be made manifest i n beetles placed under elevated! atmospheric pressure.  A  compression chamber was constructed consisting of "Lucite" plastic tubing, 40.0 cm. long and 5.0 cm. i n outside diameter and with a wall thiokness of about 6.0 mm. connector.  It was f i t t e d with a hose connection leading to a 4-way  The other passages i n the connector were Joined respectively to  a pressure gauge, an a i r bleeder valve, and a nitrogen tank. Nitrogen was used  as the compressed gas, on assumption that the normal quantity of  atmospheric oxygen -in the chamber was s t i l l available to the insects, whereas compressed a i r would have increased concentration of oxygen. This assumption follows that of Dalton's Law of partial pressure of gas mixtures. In order to judge the effect of pressure on the photic response, i t was necessary, i n accordance with other findings of the investigation, to provide attractive host tree material as a source of an opposing stimulus to the photic one.  Accordingly, a small sample of attractive wood was placed i n  one end of the compression chamber, non-flown beetles were introduced, the chamber sealed at the ends and placed i n the retaining steel "cradle . 11  Pres-  sure was b u i l t up to a maximum of 50 p s i (about two atmospheres). A beam of heat-filtered light was projected into the apparatus to cause the beetles to accumulate at the odour source, then the light was moved to the opposite end to compete with the odour for response of the beetles.  55 The apparatus for testing the response of the beetles to light under increasing atmospheric pressure i s shown i n F i g . 6. Methods of Observation The broadest problem of photic behaviour of Trypodendron may be considered.to relate to the nature and strength of orientation and other responses under various conditions of light, alone, or i n combination with other factors. The consideration should include the difference i n sex and kind of conditioning of the insect. For the study of behaviour, i t was necessary to choose appropriate c r i t e r i a by which responses could be interpreted. The responses of insects to effective external stimuli are variously manifest i n changes of the state of activity or inactivity and i n their spatial and temporal patterns. festations of responses to stimuli are observable  Mani-  in movements of appendages  or of regions of the body and displacement of the animals as a whole. Trypodendron i s capable of slight movement of i t s head i n a vertical plane, of extending, waving, and folding back i t s antennae, of manipulating i t s mouthparts for chewing or ingesting food, of waving i t s legs randomly i f the beetie i s held aloft, of coordinating them i n walking on a surface, or of folding them against the body i n feigned death, of elevating the elytra and unfolding i t s membranous wings, of restoring them to their resting position, of vibrating elytra and wings i n flight movements, and of manipulating the external genitalia as occasion befits.  Variables i n these, conceivably include the  dimensions of time, space and force, giving rise to such derived values of displacement of parts, or of the whole insect, such as rate of walking or of wing beat of f l i g h t , and various degrees of consistency i n direction or activity i n these.  The variables would give rise also to such forms of  33 A  Pig. 6. Apparatus for testing photic responses of Trypodendron under increased atmospheric pressure.  54 measurement as rates of change, and periodicities i n functions, change of orientation angle i n respect to a direction stimulus, and observations on the assumption of postures such as feigned death or preparatory stance f o r f l i g h t , boring into wood, feeding and mating. Preliminary experience i n handling the beetles suggested that certain of the foregoing manifestations of response to stimuli would be most meaningful of the single or integrated reactions of the insect to light, darkness, contact, pressure, gravity, a i r flow, temperature, and chemical and physical factors i n the host tree.  The kinds of response that were  sought included the beetles' alignment and directed movement i n respeot to directional stimuli, turning activity, retention at an odour centre or other centres of stimuli, attempts to f l y or actual f l i g h t and the compound responses of the whole insect  which are manifest i n i t s attempt to bore  into wood. Group responses were observed quantitatively i n the aggregation of beetles when a number of them were exposed simultaneously to an experiment a l situation as i n a temperature gradient apparatus. The experiments were conducted i n a darkened room. The primary purpose of the darkness i n these studies was not with the intention of adapting the insect to the condition of scotopic vision, which would involve the use of beam intensities far below the present photopic requirements, but to avoid extraneous sources of light that might interfere,with the normal response of the beetle to a given stimulus. The experiments were conducted i n a series which started i n May, 1964.  The scheme of the programme of experiments conducted i n these  studies of the behaviour Trypodendron i s presented i n F i g . 7.  55  Pig» 7. Schema of the programme of experiments on the photic responses of Trypodendron lineatum i n relation to various host wood factors and conditions of the environment o  ot  n  OVERWINTERED  A D U L T S  TIDAE)  Flown.  IAfter  U.  W H I T E  0  HORSJSONTAi. |/ B £ A W O P JUI G U P  ' Fl£LD o r LIOMTJ  Pr&seyCF  ^Sraeft," W o o d  -j  8 i n s e c i in C o n t a c t j  *fte'ct N^t»»» Contact -j"" W t ' - l r k o u t Air  }  PUEB^HT  L S 6 B T  Air  Sfrcocvr^  Source Aniipoctat t o Light j . loot/  4  \Noo<L  *Aitraci.\y/&"  Clwsfcci  ActinConW£|  Without  j  Ptre.se.wt'  j I n s e c t in C o n t a c t  A i r Stream.  h  Air Source Antipodal to LigK-t |fJe Odour in —|  g-  Sirc&m\  INCREASING-  TEMPERATURE"  D I R E C T I Oh/A L B f A M o p LlOfHT  E  G R A V  —|  iry A  IGRAVITV  PoOAM  N T I  )NCREASlMGr  I wtrw  A T M OS.  SVMPOPAUl  uidrHT  J  P R E S S U R E  g  H OC3.1 Z O N T A U SEAM  jj  Attractive  OF  Wood  MQrHT  Factors"  ]  FhgKt  NORMAL Wood •j  LABORATORY F a c t o r s  without  COIMPITIONS  A b s e n t  Air Stream.  -j A i r S o u r c e A c r o s s  I n s e c t : ,\ j -  N o Odour . n S t T ^ n ] l ^ t V ^ ' ^ m ^Sreeri* W o o d  I  P r es g t a t  [insect not m Cowfagt | | I n s e c t i n Contact ]  wriKout  A i /•  Stream.  -| A i r S o u r c e A c r o s s  - "Attractive" -1 Wt'iHou-L -j  )nse,cb  in  Cor>ttv.<yfc |  A i r Stream.  A i r Source  Across  l«. odour;» a^^l  -9  V  Present  Wood  X 1 Insect Not i i Corsk&dl  Insect  I n s e c t f-  ^'^sri'  EXEERIMEMTAL RESULTS. 1. Responses to white light under normal laboratory conditions.Both male and female Trypodendron adult beetles which had no previous f l i g h t experience showed strong positive phototaxis to a horizontal beam of white light.  There was no observable difference i n response between  the sexes as indicated by the several tracings of their paths of response to light.  Response varied from immediate orientation followed by movement  directly toward the light to feigned death and sluggish orientation followed by a circuitous or compassing movement which may or may not lead to the source of light.  Examples of paths taken by the beetles i n response to  a horizontal beam of white light are shown i f Pig. 8 (A to H) and Pig. 9 (A to H).  The responses of the beetles to the horizontal beam of white light  may be divided into four categories:  (l) not inhibited, the beetles imma*. .  diately orient themselves and move toward the source of light.  This cate-  gory of response i s exemplified i n Pig. 8 D and Pig. 9 A, 9 B, 9 C, 9 D, 9 P, and 9 H (especially by the paths of the non-flown beetles, represented by thin lines); (2) i n i t i a l l y inhibited positive response, the beetles move away for some distance from the source of light at the start of orientation, then gradually recovering and moving toward the source of light.  An example  of this particular category of response i s indicated by lines P2 i n Pig. 8 A and U2 i n Pig. 8 D; (5) inhibited positive response, the beetles may or may not be inhibited at the start of orientation but the general movement, . though toward the general direction of the source of light, i s oblique and not direct.  Examples of this category of response are indicated by lines  U5 and P5 i n Pigs. 8 B and 8 C; (4) completely inhibited response, the beetles ignoring the presence of light and the general direction of movement i s away from the source of light. 56  This particular type or category  57 of response i s indicated by lines U4 and F4 i n Fig. 8 B. In successive t r i a l s of the same individual beetle, different degrees of consistency of response occurred.  The majority of the beetles  oriented positively toward light i n every t r i a l (Pigs. 8D, 9 A, 9 B , 9G, 9 D, 9 P, and 9 H. Note especially the paths taken by the non-flown beetles).  Some beetles reacted positively i n nearly every t r i a l (Pigs.  8 A, 8 C, 8 E, 8 F, 8 G, and 8 H),  Others showed no consistent orientation  to light, and thereby demonstrated a consistency of randomness (Pigs. 8 B and 9 E), A summary of the responses of the non-flown beetles to a horizontal beam of white light i s presented i n table 1.  Table 1. Summary of responses of non-flown Trypodendron adult beetles to a horizontal beam of white light under normal laboratory conditions.  Type of response  Proportion of responses (% of t o t a l ) ^ Male  i  Female  1. Not inhibited, movement direct to light  47  52  2. I n i t i a l l y inhibited positive response  26  23  5. Inhibited positive response  21  15  4. Completely inhibited, negative response  16  10  1/ Total number of observations = 98  Fig. 8 (A to H). Representative paths of response to a horizontal beam of light by newly overwintered adult males of Trypodendron lineatum (Olivier). Thin lines, marked *TJ , represent paths of flight-inexperienced beetle; thick lines, marked •T??, represent paths of the same beetle after flight exercise. Numbers represent type of response (see table l ) . tt  Direction of l i g h t  Direction of light  Direction of light  |  Direction of light  Figure 8 D Specimen: male "beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : ' 50 min.  Direction of light  Figure 8 E. Specimen: male beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 1 hour  1  Direction of light  Speoimen: male beetle Ammeter at 4.0 amperea Light, heat f i l t e r e d Duration of f l i g h t : 1 hour i i  Direction of light  PS  Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 2 hours  Direction of light  U2 U3  Figure 8 H. Specimen: male beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : SO min.  59  P i g . 9 ( A t o H ) . R e p r e s e n t a t i v e p a t h s o f r e s p o n s e t o a h o r i z o n t a l "beam o f w h i t e l i g h t by newly o v e r w i n t e r e d a d u l t females o f Trypodendron lineatum ( O l i v i e r ) .  T h i n l i n e s , marked b y " U " , r e p r e s e n t p a t h s o f  flight-inexperienced beetle; p a t h s o f the same b e e t l e  t h i c k l i n e s , marked " P " , r e p r e s e n t  after f l i g h t  t y p e s o f response (see t a b l e  l).  exercise.  Numbers r e p r e s e n t  Direction of light  U2j  F4  Figure 9 A. Specimen: female beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 15 min.  D i r e c t i o n of light  Figure 9 C. Specimen: female beetle j&arter at 4.0 amperes Light, heat f i l t e r e d N a t i o n of f l i g h t 1.0 hour.  Direction of light  4  Ul  U2 P2 U:. Ul  P5, Ul  fi  P4  Direction of light  Specimen: female beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 50 min.  Direction of light  Direction of light  Figure 9 G. Specimen: female "beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 2.0 hours  Direction of light  Figure 9 H. Specimen: female beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 50 min.  The beetles that were given flight experience varying from five  40  minutes to six hours showed various degrees of inhibition of their response to a horizontal beam of white light.  Inhibition was more apparent i n the  female beetles than i n the males which behaved as i f they had not flown. Examples of the path taken by the flight-experienced beetles i n response to a horizontal beam of white light are shown i n thick lines i n Figs. 8 (A to H) and 9 (A to H)-. Responsiveness, to light i n the female beetles i s not, howiever, completely lost or totally inhibited as a result of f l i g h t experience even when the, duration of f l i g h t experience i s increased.  Several beetles  which had been given f l i g h t experience of more than six hours s t i l l exhibited positive response to light. A summary of the responses of the flight-experienced beetles i s shown i n table 2.  Table 2. Summary of responses of flight-experienced Trypodendron adult beetles to a horizontal beam of light under normal laboratory conditions.  Type of response  1. Not inhibited, movement direct to light  Proportion of responses (& of t o t a l ) ^ Male j Female 45  22  2. I n i t i a l l y inhibited positive response  25  16  5. Inhibited positive response  21  50  4. Completely inhibited, negative response  15  52  1/ Total number of observations = 95  41 After the tests f o r the simple photic responses of flight-inexperienced and flight-experienced beetles to a horizontal beam Of white light, another set of beetles was exposed, tinder normal laboratory conditions, to overhead light. The beetles took to f l i g h t i n the presence of a broad f i e l d of light from above. The time differences between setting (putting the beetles on a fixed position at the center of the piece of paper) and taking to f l i g h t was not determined, although i t was noted that previous f l i g h t experience did not inhibit the beetles from taking to f l i g h t again. Representative samples of response of the beetles to an overhead source of light are shown i n Fig. 10 (A to D).  The paths of the f l i g h t -  experienced beetles were i n several instances punctuated by pauses or rests. Orientation was consistently random. 2. Photic response i n the presence of a i r current with or without wood odour.The introduction of a gentle stream of a i r flowing at the rate of about 0.5 meter per second did not alter the response of the beetles to light. Neither did an airstream passed through sawdust of "green" host wood. However, when the airstream was passed through a mass of shavings from "attractive" host wood, both non-flown and flown beetles immediately abandoned their course toward light i n favour of the odorous airstream.  Samples of  these responses are illustrated i n Fig. 11 (A to D). In the presence of an overhead source of light, the beetles also responded positively to the airstream carrying odour from the mass of shavings of attractive host wood. The response, however, of the flight-inexperienced beetles was of short duration and was readily overcome by the positive response to light.  The flight-experienced beetles took much longer time i n  Fig. 1 0 (A to D). Representative paths of response to an overhead source of light by newly overwintered adults of Trypodendron lineatum (Olivier) Thin lines represent paths before f l i g h t and thick lines after f l i g h t  Figure 10 A. Specimen: female "beetle . Lighting: ceiling f lioorescent lamps Duration of f l i g h t : 10 min.  flew 1 A stopped  Specimen: male beetle Lighting: ceiling fluorescent lamps Duration of f l i g h t : 50 min.  Pig. 11 (A to D). Representative paths of flight-inexperienced (represented by thin lines) and flight-experienced (represented by thick lines) adult Trypodendron In response to a gentle stream of a i r (x) without odour, and (o) with attractive wood odour.  Direction of light  o  e  o  6  6 6 0  o o o  3.  Figure 11 A. Before f l i g h t B. A f t e r f l i g h t Specimen: male beetle L i g h t , heat f i l t e r e d Duration of f l i g h t : 1.0 h r .  I o  I I  D i r e c t i o n of stream of a i r  y= course taken i n s t i l l a i r r. - course taken while odourf r e e a i r flowed from behind, o = course taken while attractant was blown toward l i g h t .  Direction of light  A-  x  r  Figure  U.  C. Before f l i g h t D. After f l i g h t Specimen: female beetle Light, heat f i l t e r e d Duration of f l i g h t : 30 min. y = course taken i n s t i l l a i r x = course taken while odourfree a i r flowed from behind, o = course taken while attractant was. blown toward light.  Direction of a i r stream  44 investigating the source of the a i r carrying the attractive host odour. They, too, however, eventually abandoned the source of the airstream and became positively attracted to light. 5. Photic response i n the presence of "green" wood f actors.The presence of the various stimuli provided by "green" wood such as odour or contact did not alter the response of the beetles to either a horizontal beam of white light or an overhead light source. The responses of the flight-inexperienced and flight-experienced beetles were similar to previously observed responses of the beetles where "green" wood host factors were absent. A slight change i n the behaviour of a few flight-experienced beetles was noted when the beetles were individually placed i n contact with a "green" piece of wood. The change was characterized by some indication of investigative behaviours  the beetles occasionally hesitated i n their move-  ments, paused, manipulated their antennae while s t i l l on the surface of the wood. The exhibition of investigative behaviour was not, however, of long duration, whereas attraction to light or to an airstream wood odour was pronounced,,  carrying attractive  Representative paths of response exhibited by the  beetles i n contact with "green" wood or i n the presence of "green" wood and other factors involved with i t are illustrated i n Pigs. 12 (A to D) and 15 (A to D). 4. Photic response i n the presence of attractive wood factors6Response of the flight-inexperienced male or female Trypodendron to either a horizontal beam of white light or an overhead light source was invariably inhibited by the presence of an attractive piece of wood under the perforated area at the center of the sheet of paper where the beetles were individually set for observations.  In some instances the beetles were only  F i g . 12 (A to D), Representative paths of response to light and to an airstream with (marked "o") or without (marked "x") attractive wood odour by flight-inexperienced (U) as well as flight-experienced (F) adults of Trypodendron placed on a perforated area on a sheet of paper above a piece of "green" wood.  Miecfcioti of light  Direction of a i r stream  Direction of light  Direction of a i r stream  Direction of light  Figure 12 C. Specimen: female beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 10 min.  Direction of a i r stream  Direction of light  Direction of air stream  46  Fig. 15 (A to D) O Representative paths of response to light and to an airstream with (marked o") or without (marked "x") attracM  tive wood odour by flight-inexperienced (U) as well as f l i g h t experienced (F) adults of Trypodendron i n direct contact with a piece of "green" wood* wood was not recorded.  The course taken by the beetle on the  D i r e c t i o n of l i g h t  Figure 13 A.  8  \  Specimen: female "beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 30 min.  Direction of a i r stream  Direction of light  Figure 13 B. Specimen: female beetle Anmeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 1 hr.  t  Direction of a i r stre m a  D i r e c t i o n of l i g h t  Figure 13 G. Specimen: male beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 30 min.  D i r e c t i o n of a i r stream  Direction of light  Figure 15 D. Specimen: male beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 1.0 hour  / i  /  I  I  I I  Direction of a i r stream  47 i n i t i a l l y inhibited, f o r a very brief period of time before they moved toward the  source of light or attempted to f l y away., In other instances^ they  lingered on the perforated area, moved slowly, and took a convoluted course (see Fig. 14 A and B).  Investigative behaviour was exhibited but not  pronounced. Response of the flight-experienced male or female Trypodendron to such conditions as mentioned i n the preceding paragraph was characterized! by an apparent i n i t i a l indifference to light and by a certain high level of excitability i n the display of investigative behaviour. Investigative behaviour took the form of very convoluted paths of movement on the perforated area of the paper above the attractive piece of wood. The time spent by the beetles walking on the perforated area varied from a few minutes to more than half an hour (a period of time set arbitrarily as the limit f o r the purpose of the test).  After a period of time on the perforated area,  the beetles wandered away or became attracted to light. Examples of the path of response of the flight-experienced and flight-inexperienced beetles to light i n the presence of attractive wood underneath a perforated paper are shown i n Figs. 14 (A and B), 15 (A and B) and 16.  It was noted that the flight-experienced beetles were f a r more  reactive than the flight-inexperienced individuals to a source of attractive wood odour.  In s t i l l air, there was a consistent display of investi-  gative behaviour expecially on the perforated area of the sheet of paper just about the region where the sapwood portion of the piece of attractive wood l i e d underneath (see Fig. 14 A). One observable effect of directing a stream of non-odour-bearing air to the perforated area was a dissipation of wood odour as manifested  48 by a decrease i n the density of responses to a particular area (see Pig. 15 A) or by baok-and-forth paths of responses (see Pig. 15 B). The introduction of an airstream conveying an attractive wood odour had about the same effect as a non-odorous airstream.  One notable difference,  however, was the presence of minor concentrated responses and inclinations to approach the source of the stream of odour (see Pig. 16). The responses of the flight-inexperienced beetles to light when they were individually placed i n contact with the piece of atifcractive wood varied from a very brief period of retention by the wood to a few positivenegative responses to i t but f i n a l l y attraction to light predominated. Response to a non-odorous a i r current was n i l ; to an airstream conveying the attractive odour, i t was positive. The flight-experienced beetles exhibited a very strong investiga?tive behaviour when they were individually placed i n contact with attractive wood. They were excited, active, and mobile. They explored a l l sides of the wood, at times moving away from i t but returning again.  This type of beha-  viour was exhibited f o r a variable period of time before the beetles f i n a l l y moved away or became attracted to light.  An introduction of an airstream to  the area on the piece of wood where the beetle was located did not alter i t s response as i t did when the beetle was not i n contact with the wood. The response to an airstream conveying attractive wood odour was variable; many of the beetles tested did not move away from the attractive piece of wood, while others were drawn to the source of the airstream for a short period of time. Representative paths of response of the beetles i n contact with an attractive piece of wood i n the presence of white light are illustrated i n  Pigs. 17 (A and B), 18 (A and B) and 19. 5. Response to background black-and-white patterns.The series of tests vising ( l ) horizontal black-and-white broad lines> (2) vertical black-and-white broad lines, (5) diagonal black-andwhite broad lines, (4) a l l black, or ( 5 ) a l l white background pattern while the beetles were individually exposed to a horizontal beam of white light did not produce results which showed any marked preference or tendency by the beetles to.respond to any of the patterns. 6. Responses to white light under increasing temperature.Tests of the photic responses of flight-inexperienced adult Trypodendron at temperatures ranging from 14° to 40°Q, with the beetles inside a painted glass tubing placed on a temperature gradient apparatus, indicated that the peak of activity characteriaed by excitability, positive phototaxis, and attempts to f l y occurred between 26° and 28°G. the beetles ceased to become attracted to light entirely.  At 58°<3  The results of  10 tests, using 10 beetles i n each test, are shown i n table 5. I n the tests f o r responses of the beetles to light, antipodal to gravity, under increasing temperature, the range of temperature under which the responses of the beetles were studied was from 25° to 40°C  In these  tests, the peak of activity of the beetles was noted at about 29°C.  The  maximum temperature which registered a positive photic response by the beetles was 36°G.  In only one instance out of 10 tests did a beetle appear  at the lighted window at 56°G. and 35°G.  Mating occurred occasionally between 25°  These pairs were indifferent to light. In the tests f o r responses of the beetles to light positioned  sympodally with gravity, the range of temperature registering the highest  50  Pig. 14 (A and B). Representative paths of responses to light and to an attractive piece of wood under perforated area on sheet of paper by flight-inexperienced (indicated by thin line) as well as flight-experienced (indicated by thick line) Trypodendron lineatum.  Direction of light  Figure 14 A. Specimen; female beeile Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 30 min.  c  Direction of light  51  Pig. 15 (A and B). Types of response to light and to an airstream without attractive wood odour by flight-inexperienced (indicated, by thin line)  and flight-experienced Trypodendron  beetle on  a perforated sheet of paper above an attractive host wood.  Direction of light  Direction of light  Figure 15 B. Specimen: Female beetle Ammeter" at 4.U amperes Light, heat f i l t e r e d Duration of f l i g h t : 15 min.  Direction of a i r stream without wood odour  16. Representative paths of response to light by flight-inexperienced (thin line) and f light -experienced (thick line) adult Trypodendron beetle placed on a perforated sheet of paper above attractive host wood and subjected to a gentle stream of a i r with attractive wood odour.  Direction of a i r stream with "ripe" wood odour  53  F i g . 17 (A and B) „ Representative paths of response to light by the flight-inexperienced (thin line) or by the flight-experienced (thick line) Trypodendron beetle i n contact with a piece of attractive host wood. Tracings were made of paths as beetle wandered away from the wood  0  Figure 17 A. Specimen: female beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t ; 5 hours  Direction of light  Figure 17 B.  Specimen: male beetle Ammeter at 4.0 amperes. Light, heat f i l t e r e d Duration of f l i g h t : 1.0 hour  54  Pig„ 18 (A. and B)« Representative paths of response of flight-inexperienced (indicated by thin broken line) and of flight^sxperienced (indicated by thick broken line) adult Trypodendron beetle to light and to a stream of a i r with attractive wood odour 0  Beetle m s i n contact  with wood and i t s path was traced whenever i t l e f t the wood.  Direction of light  I I \  \  \  1  v \/  / .W/  y  J2—i. "Ripe?., wood  '" -^ ,r  (  V  \ Figure 18 A. Specimen: female beetle Ammeter at 4 . 0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 5 hours Direction of a i r stream with attractive wood odour  ion of light  Figure 18 B. Specimen: male beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d IXu-atioa of f l i g h t : 40 min. S e c t i o n of  ^  19« Representative paths of response of the flight-experienced Trypodendron beetle placed i n contact with a piece of attractive wood i n relation to light i n the presence of an airstream without (indicated by dotted line) or with attractive host wood odour (indicated by dashed l i n e ) .  Direction of light  Figure 19 Specimen: female beetle Ammeter at 4.0 amperes Light, heat f i l t e r e d Duration of f l i g h t : 45 min. s response to a i r without odour. - - - = response to a i r with attractive wood odour  4* .  i  :  i  \  I  : I Direction of  56 percentage of beetles responding to light was 25° to 28°C. The maximum temperature registering the least number of beetles responding positively to light was S6°C. In some tests, increasing temperature caused the beetles to become very active or "excited". Attempts to f l y were noted i n many instances. Thermal paralysis and death of several beetles occurred between 56° and 58°C. The summarized data on the responses of the beetles to light i n relation to gravity and increasing temperatures are shown i n table 4. They are also illustrated i n Pigs. 20 and 21.  Table 5. Photic responses of adult Trypodendron under increasing temperature i n a glass tubing on a gradient apparatus.  Temperature range G  Per cent of beetles responding positively to light  14 - 16  55  17 - 19  75  20 - 22  83  25 - 25  83  26 - 28  85  29 - 51  61  32 - 54  52  35 - 57  56  58-40  '  0  57 Table 4. Photic responses of adult Trypodendron as influenced by gravity and increasing temperature M Temperature range  G  Per cent of beetles responding positively to light a. Light antipodal : b. Light sympodal to gravity with gravity  25-25  81  85  26 - 28  85  85  29 - 51  ,86  70  52 - 54  58  44  55 - 57  18  17  58-40  0  0  1/ Average of 10 tests per temperature rangej 10 beetles per test.; 7. Responses of Trypodendron to various stimuli i n the dark.Under normal laboratory conditions, newly overwintered Trypodendron adults, having f l i g h t experience or not, moved about i n a random manner when placed inside a dark box.  The same results were obtained when a stream of  a i r was allowed i n and out of the box through tiny holes.  However, when the  airstream carried attractive wood odour, the beetles tended to approach the hole through which the a i r stream was introduced. Physical contact with a piece of "green" wood placed inside the box did not cause an aggregation or positive response of the beetles. The majority of the beetles had moved away from the piece of wood after the allotted time of five minutes allowed f o r each test.  Again the introduction of an  airstream without wood odour did not change the i n i t i a l behaviour of the beetles.  Positive response, however, was observed when the airstream carried  attractive wood odour.  Fig. 20. Effect of increasing temperature on the photic responses of Trypodendron lineatum (Olivier). Fig. 21. Comparison of effects of gravity and increasing temperature on the photic responses of Trypodendron lineatum (Olivier).  Temper at tare range i n degree centigrade  59  Attractive wood inside the box caused an aggregation of the beetles on or near the wood. During the period of observation, some  of the beetles;  crawled under the wood while others were either away from i t or at the base of contact of the wood with the sheet of paper. No boring behaviour was observed during the period allowed for each test.  However, i n a test i n  which the beetles were oonf ined to a piece of wood covering i t with a suitable stacking dish and l e f t overnight, preliminary borings were observed.  DISCUSSION QP RESULTS 1. Photic behaviour i n Trypodendron; i t s ecological significance and i t s underlying mechanisms.The response of Trypodendron adults to light at the end of their overwintering period has been shown by these studies and by previous other observations (Graham, 1959) to be strongly photopositive. Furthermore, the tests have shown that the beetles' a b i l i t y to orientate to the source of light i s i n no way affected by their i n i t i a l angular displacement. The expression of positive phototaxis appears essential at this particular stage of the l i f e cycle of the beetles.  After overwintering, residence i n the  forest l i t t e r or loose bark not only ceases to function advantageously f o r the insect, but would frustrate i t s survival i f special sequences i n behaviour did not cause i t to disperse and react to host factors* The presence of a narrow horizontal beam of light attracts Trypodendron. „ Positive response i s often characterized by an increase i n the locomotory speed toward the source of light.  At some point i n the expression  of positive phototaxis or at a certain distance from the source of light, the beetles may be stimulated to f l y . Another condition which stimulates f l i g h t i s the presence of a broad overhead f i e l d of light as provided by ceiling lamps or by skylight.  The importance of an overhead source of light  i s shown by the fact that when the beetles were, exposed to light coming from below their horizontal plane of sight, f l i g h t did not occur * Restoration of an overhead source of light caused i n i t i a t i o n of f l i g h t s . In the laboratory, escaped beetles were observed flying continuously about the ceiling lights, at times even when their heads i n touch with the fluorescent light tubes. The light intensity close to the light tube was 60  61 of the order of 500 footcandles.  In nature, ordinary sunlight produces an  iiTuminance of some 10,000 to 14,000 footcandles (Piatt and Griffiths, 1964). Under f i e l d conditions, the beetles do not f l y upward into the sky.  At most/  they have been observed flying up to about six to seven meters from the ground i n forest areas with an elevation of about 400 meters above sea level (Chapman, 1962). One conceivable explanation f o r the beetles* not f l y ing  toward the sun may be that they f l y ,  angle to the rays of light.  like many other insects, at a certain  This type of light reaction i s termed light  compass reaction (Fraenkel and Gunn, 1961). It i s also possible that there is an upper limit i n the threshold of light intensity which the photoreceptors of the beetles can tolerate. The occasional negative phototactic response among positively phototactic beetles has been observed (see table l ) .  Why i t should exist  among flight-inexperienced beetles which generally are positive i n their light responses remains among other questions to be answered. I t i s conceivable  that i n these individuals, diapause influences are s t i l l partly operative,  or reproductive maturity i s delayed. Positive phototaxis i n Trypodendron i s not a unique behaviour. Photic attraction i s involved i n various activities among different insects. F i r e f l i e s , for instance, though nocturnal i n activity also exhibit positive phototaxis i n attracting or locating a mate (KcElroy, 1964). In the moths, however, i t i s s t i l l unexplained as to why these nocturnal insects are attracted  to light at night but not to sunlight i n the day.  Winged termites, on  the other hand, utilize their brief positive phototactic behaviour as a means to disperse and possibly interbreed with members from different termite colonies of the same species.  L i t t l e i s known directly of the mechanisms which trigger light attraction i n Trypodendron although much has already been studied and written about photoreception i n many species of insects (Birukow, 1961; Booth, 1965j Burtt and Catton, 1956, 1962; Grescitelli and Jahn, 1959,  1942;  Dethier, 1955d; Fingerman, 1952; Goldsmith, 1964; Rogers, 1962; Ruck, 1965; de Vries, 1956; de Wilde, 1962). One of the factors known to influence the expression of phototaxis i n some insects i s hormone concentration. Beetsma et a l (1962) found that injections of an extract of the abdomen of male cecropia moth into fourth and f i f t h instar larvae of a hawk moth shifted the balance between photopositive and photonegative tendencies towards a definite photopositive response.  In the Colorado potato beetle, activity of  the corpora allata has been correlated with positive phototaxis (de Wilde, 1959) . Photonegative response was also demonstrated by implantation of active prothoracic glands into the body cavity of the caterpillars. conceivable that i n some of the newly overwintered Trypodendron  It i s  adults the  prothoracic gland s t i l l exerts an inhibiting influence on the photic behaviour of the beetle. In some other insects, light attraction i s tied with homeostatic processes which regulate the physiological and biochemical functions of the various internal organs. Thus the larvae of several species of tent caterp i l l a r s , Malacosoma distria, M. pluviale and of the f a l l webworm Hyphantria textor on becoming hungry are attracted to light and crawl up to the top branches where there i s young foliage to feed on (Sullivan and Wellington, 1955; Wellington et a l , 1954). A similar light attraction enables the adults of white pine weevil, Pissodes sbrobi, to climb to the terminal shoots or leaders which they infest (Sullivan, 1959). These observations  suggest possible approaches to the study of physiological mechanisms i n photic responses i n Trypodendron. One important observation on the behaviour of Trypodendron that needs derivation from known physiological characteristics of organ systems i n insects i s the mechanisms which stimulate the beetle to f l y .  I t appears  that the amount and intensity of light f a l l i n g on i t s photoreceptors may be involved i n the f l i g h t - i n i t i a t i n g mechanisms. I t i s also possible that the photoreceptors have a threshold number which triggers the flight response. Pielou (1940) believes that i n the beetle Tenebrio molitor, there i s a relation between threshold of response and the number of sensiHa stimulated. The failure by a broad f i e l d of light coming from below the horizontal plane of sight of the beetles to stimulate the beetles to f l y seems to support the foregoing statement. Another explanatiork relevant to the beetle's failure to f l y i n the presence of "sunken" light involves differences i n the thresholds of stimulation or i n the a b i l i t y to d i s c r i minate light between the dorsal and ventral part of the eyes of insects whose eyes are divided into two portions (Burkhardt, 1964).  Trypodendron  has divided eyes. 2. The modifiers of photic behaviour; their.-relation to host^fihding.^ The failure of a non-odour-bearing airstream to modify the activity of Trypodendron beetles moving toward the source of light indicates that the airstream alone has no inhibiting effect on the phototactic beha*r _ viour of the beetles, nor does i t e l i c i t a positive anemotactic response. This conforms with statements by Dethier (1957) i n his review on the orientation by some f l y i n g insects that a i r current alone does not initiate  64 orientation.  This statement was supported by observations made on the  behaviour of diverse kinds of insects such as Drosophila, a f l y ; Geotrupes ^ i. stercorarius, a beetle; and Bombyx mori, a moth. ,In these insects, i t i s odour which initiates orientation to a i r currents.  In our own studies,  pedestrian Trypodendron adults responded to an airstream carrying attractive wood odour. Their positive phototactic behaviour was immediately inhibited on their being exposed to an airstream carrying attractive wood odour. Their response, however, was variable i n the duration of time they stayed at the odour source.  The beetles approached the orifice of the a i r source  but eventually l e f t i t to proceed toward light.  On the basis of this  observation, one may postulate the need for other kinds of stimuli that must be present i n order to retain the beetles at the odour source. The failure of the beetles to react to an airstream when they are already surrounded by odour appears at f i r s t to be contrary to expectations.  I t does not appear to correlate with their ^response to an odorous  airstream brought into an odour-free " f i e l d " .  It also tends to contradict  the suggestion that an anemotactic response occurs.  It should be remembered,  however, that these studies pertain to a pedestrian situation i n which the tactile stimulus of the insect i n contact with a'surface may under certain conditions inhibit an anemotactic response. If the beetles reacted otherwise, they Would be biological failures, abandoning  attractive host mate-  r i a l every time a breeze blew across i t . At least two considerations might be discussed i n connection with the foregoing statements: ( l ) conditions within the beetles and (2) tions within the host materials.  condi-  :  65  Granting that a l l conditions within the host material meet the requirements of the beetles, i t seems that the beetles s t i l l must go through a series of stereotyped responses starting with positive phototaxis, f l i g h t , orientation to an airstream carrying attractive wood odour, approach to the source of the odour, settling and crawling before being able to bore into the host material. Graham (1959) indicated that f l i g h t exercise could effect an inhibition of the phototactic response of the beetles. Flight-exercised beetles were no longer strongly photopositive, and when put i n contact with an attractive pieoe of wood, the beetles behaved normally by exploring the bark contours and eventually boring into wood. While the present study did confirm that f l i g h t and the presence of attractive wood inhibit the positive phototactic behaviour of Trypodendron, i t did not, however, show such strong depression of the phototactic reaction, nor the strong tendency to bore into attractive wood. The reason for the disparity of results i s not clear.  It may have to be sought i n  differences i n the population stock, conditions of storage or unrecognized differences i n the environmental conditions during the experiments. There appears to be present i n the behaviour pattern of Trypodendron another mechanism of responses leading to the boring into wood. For instance, Graham (1959) observed that beetles which had no previous flight experience when kept i n the dark with a piece of attractive wood exhibited the boring behaviour „ Chapman (1959) and Dyer and Chapman (1965) reported that newly overwintered,,flight-inexperienced beetles could be forced to bore into attractive logs but not into "green"/logs when confined to the upper surface of logs i n small aluminum rings partly imbedded i n the  66 surface of the logs. While Graham's observations noted borings made i n the dark, Chapman and Dyer's did not note whether the  borings were made during  the day or during the night. Neither, however, excluded the possible effect of locomotion by prolonged walking or crawling on responsiveness to light or to i t s host as observed by Johnson (1958) i n connection with the settling responses i n aphids. The importance of f l i g h t experience preparatory to host attraction under normal conditions has been noted i n insects other than Trypodendron. In aphids, Kennedy (1955, 1958) and Kennedy and Booth (1965a, 1965b) observed that f l i g h t experience "primes" or promotes the settling response on a host leaf.  A suitable host leaf i t s e l f was considered to possess an inhibitory  stimulus that would cause the aphid to remain. the insect would take to f l i g h t again.  If the leaf were unsuitable,  The "excitability of* the.;settling  responses increased as an aftereffect,of f l i g h t i n whioh the excitability of f l i g h t i t s e l f (measured by the rate of climb) was not f a l l i n g and was even increasing." As regards the effect of flight on phototaacis, Kennedy (1965) believes that, i n aphids, "at first.the phototaacis i s positive to a l l light intensities, but that as f l i g h t proceeds i t becomes negative to bright light while s t i l l remaining positive to weaker light, u n t i l f i n a l l y i t becomes negative even to the dimmest light and the reversal can then be said to be complete." Several suggestions have been advanced to explain the underlying mechanisms which cause the settling and feeding behaviour as an aftereffect of f l i g h t . ,Evans and ^ethier (1957) and Hudson (1958) are of the opinion that f l i g h t , especially i n the blowfly and the honeybee, causes a diminution  67 of blood trehalose and glucose levels resulting i n the lowering of the threshold f o r feeding. Johnson (1958) also suggests that respiratory metabolism has an effect on the settling responses as he found that aphids increased readiness to settle after a brief anaesthesia with carbon dioxide but not' with ether. These suggestions appear to come under the "peripheral * hypo1  theses which, according to Kennedy and Booth (1963b), are "versions of the chain-reflex theory of behaviour assuming that the link l i e s not i n the central nervous system but i n some cumulative physiological consequence of the locomotor activity which provides 'feed-back' •" Kennedy (1Q65) believes, however, that the mechanism l i e s i n the cental nervous system and i s controlled by i t , "over and above any peripheral feed-back from f l i g h t such as a i r swallowing and gut distension seem to provide." As to the composition and make-up of the set of stimuli that must be present i n the host material before a "conditioned" or "primed" insect could show a favorable response, Beck (1965) suggests that they are biochemical and biophysical i n nature.  He gives the following classification of  stimuli which influence different feeding responses: Type of response  , 1  Evoking stimulus Positive  Orientation  Attractant  Orientation  Arrestant  Biting or piercing  Incitant  Maintenance of feeding  J  Stimulant  a  f  T I  J | 1  Negative Bepellent Repellent Suppresant Deterrent  Beck defines an "attractant" as any stimulus which attracts the insect by orienting movement toward the source. 1  An "arrestant" i s said to  cause an insect to cease locomotion i n close contact with the source, while  68  an "incitant" i s a stimulus which evokes a biting or piercing response. The negative responses are caused by a set of stimuli, termed differently, which prevent or inhibit the positive responses. A considerable amount of work has been done on host-finding and selection by many phytophagous and parasitic insects (Beck, 1957$ 1960, 1965, 1965; Brues, 1946; Dethier, 1941, 1947a, 1947b, 1951, 1952a, 1952b, 1955a, 1953b, 1954, 1955, 1957, 1962, 1963; Dethier and Rhoades, 1954; Fraenkel, 1955, 1959; Ham&mura, 1959; Harris, 1960; Howe, 1950; Ibbotson and Kennedy, 1959; Kennedy, 1955, 1958; Kennedy and Booth, 1951, 1965a, 1965b, 1964; Kennedy et a l , 1959a, 1959b, 1961; Idpke and Fraenkel, 1956; Loschiavo et a l , 1965; MacGregor, 1948; Merker, 1955; Ohnesorge, 1955; Painter, 1958, 1965; Thompson and Parker, 1927; Thorsteinson, 1955, 1958a, 1958b, 1960; de Wilde, 1958). In Trypodendron, neither the nature of the so-called "incitant" which would cause the beetle to begin boring, nor the other sets of stimuli i n the series, nor their corresponding inhibitory counterparts are known. The effect of increasing temperature i n the environment on the phototactic behaviour of various insects has always been that of reversal (Jack and Williams, 1937; Green, 1954; Pertunnen, 1959; Pertunnen and Paloheimo, 1965, 1964; Rudinsky and Vite, 1956; Wellington, 1948; Wellington et a l , 1951, 1954). The results of the tests on Trypodendron show that the beetles shun the light at temperatures above 58°C. The term "photic reversal" i n the sense of a permanent change from photopositive to photonegative or vice versa as a result of high temperature may not be an applicable term for Trypodendron. Photic inhibition may be a more appropriate term because the beetle ..does not really become negatively  69 phototactic as indicated by the fact that they s t i l l respond positively to light when returned to ordinary temperatures. The apparent effect of high temperature under f i e l d conditions on the photic response of insects may not actually be a reversal of phototaxis but a different response which prompts the insects to escape from heat which i s correlated with the most intensely illuminated condition.  Should, however, the temperature i n the shaded area  be higher than or equal to that i n the exposed area, the insect would likely, as does Trypodendron move about, even venturing to light, i n search of a favorable temperature. Photic reversal seems to persists, as i s manifest i n flown termites or i n Trypodendron as i t begins to bore a tunnel into wood, or i n the last instar larva of the hawk moth as i t digs into the ground i n orderto pupate (Gilbert, 1964). Positive geotaxis i s often correlated with negative phototaxis, especially i n many plant-climbing insects.  This i s particularly true of  the larvae of lepidopterous and of hymenopterous insects.  However, many  of the non-plant-climbing insects may become photonegative i n their response to light without becoming positively geotactic.  This i s indicated by the  photonegative responses of the beetles at high temperatures (up to 57°C) when light was sympodal with gravity (see table 4). The failure of the elevated atmospheric pressure to simulate the effect of the swallowed gas bubble i n reducing the photic response showed that pressure per se i s not involved.  One must therefore contemplate the  possibility that stretch effects on the gut wall or on the body wall are involved (Pinlayson and Lowenstein, 1955).  70  Insects are generally classified as either diurnal, crepuscular,  or nocturnal i n habits depending on the time of the day they are most active. While Trypodendron i s definitely diurnal i n habits, expecially i n so f a r as emergence and f l i g h t are concerned, they are nevertheless active i n the absence of light.  The activities of these beetles i n the dark include  copulation, orientation by crawling toward and attractive odour source, boring into a suitable piece of wood, feeding and oviposition. While the behaviour of the beetles i n the dark i n relation to a suitable piece of wood or to:an attractive'bdour i s similar to the behaviour of the.flight-experienced beetle ;ih\the:.presence:rbfilight^tha i n t r i n sic motivating stimulus acting on the beetle i n the dark may be entirely different from the "priming" effect of f l i g h t .  As already reported, flight  results i n the expenditure of energy by the insect (Pringle, 1965j Sacktor, 1965), accumulation of a gas bubble i n the ventriculus (Graham, 1961), and consequent physiological and/or physical effects (Chapman, 1956) responsible for lowering some thresholds which permit the beetle to settle on and bore into a suitable piece of wood. What "primes" the beetle i n the dark i s not known. I t appears that the physiological, biochemical, and physical changes brought about by flight are too much for the flight-inexperienced" beetle to attain or obtain i n the dark.  These observations suggest that  there must be other mechanisms involved and that the importance of the central nervous system as stipulated by Kennedy (1965) i n governing the behaviour of the beetles i s not to be overlooked. The retention of beetles on perforated surfaces separated from attractive wood by a shallow space, as well as their ready response to a stream of a i r passing over attractive' wood but not over green wood can be  71 explained only on the assumption that odour i s the prime factor involved* The similarity of responses of males and females to the odour from attractive hut non-attacked -wood demonstrates the existence of an effective primary  attractant originating from the wood alone.  This i s not to say,  however, that secondary attractants may not play an important role i n increasing subsequent frequency of attack (Rudinsky and Daterman, 1964a, 1964b) • The retention of the flown beetles i n a f i e l d of odour above attractive wood i s characterized by their decisive return to the f i e l d of odour after transgressing the boundary of that f i e l d into an odourless; area (see Pig. 15).  This reaction suggests either a memory for position,  or a direction-reversal when the olfactory stimulus diminishes or f a i l s , or an ability to detect a gradient within a very short radius. Dethier (1957) mentions that i n Bombyx mori a strong drop i n odour concentration while the insect i s responding to an odour stream results i n elimination of stream orientation. The continued photopositive response of T. lineatum even when placed i n contact with, green wood, or i n a f i e l d of odour from i t ^ or i n a directed stream of odour from i t allows several possible inferences. Either attractants are not present i n stimulating concentrations or they are present but are obscured or rendered ineffective by repellents or olfactory inhibitors.  Bow the inhibition of the photic response of f l i g h t -  experienced beetles when brought into contact with attractive wood or odour from i t may signify the formation de novo of olfactory attractants from non-attractive or even from repellent precursors, or i t may signify the disappearance of repellents which prohibit the action of pre-formed attractants, or i t may mean that repellents are i n i t i a l l y present which convert  72 to attractants. The questions are largely resolved by consideration of the fact that olfactory attraction of attractive wood was retained even when i t was admixed with a large proportion of "green" wood. This indicates that i f repellents or olfactory inhibitors exist, they are not present i n significant quantities i n "green" wood. This being so, one may then conclude that attractants are not present i n "green" wood, for i f they were, their effect would have been manifest because there i s evidently nothing i n "green" wood to prohibit any attractants i n i t from e l i c i t i n g a response. 5. Aspects of behaviour of Trypodendron which are useful i n bioassay techniques.Previous investigations on attractancy of materials for T. lineatum depended on the beetle boring into wood. The technique consisted of placing female beetles i n darkness on either bark-covered slabs of wood or half-inch thick transverse sections of wood which were treated i n various.ways with test chemicals.  It may be assumed that a boring-in response depends not only upon  attractancy for the olfactory sense, but also upon factors of texture and taste. The boring-in test i s therefore not ideally suited for detecting purely olfactory stimuli.  It has other disadvantages.  It i s suitable only for female  beetles, since i t i s only the females of this species which initiate and carry out tunnelling.  It i s therefore costly of potential experimental specimens.  Furthermore, for s t a t i s t i c a l reasons, each t r i a l should be based on the proportional responses of at least 10 individuals introduced simultaneously.  Another  disadvantage i s that there i s a considerable time lag i n obtaining a decisive indication of response, and this interval of lag varies considerably between individuals.  A period of about 24 hours i s often required before the responses  of the beetles can be decided.  During this interval, pronounced chemical changes  73  may occur i n the m a t e r i a l being t e s t e d .  I f t e x t u r e , t a s t e , and other f a c t o r s  as yet not understood, are u n s a t i s f a c t o r y , o l f a c t o r y a t t r a c t a n t s may not y i e l d a response.  On the other hand, the t e s t has the . advantage of not r e q u i r i n g  c l o s e and constant observation of the b e e t l e s .  I t has a f u r t h e r advantage i n  that the holes bored by the b e e t l e s provide a permanent r e c o r d of t h e i r response. This type of t e s t can be set up w i t h non-flown females confined i n the dark w i t h the t e s t m a t e r i a l .  This bypassing of the need f o r f l i g h t that would be  r e q u i r e d f o r study of responses i n the l i g h t s i m p l i f i e s the procedure and ensures more u n i f o r m i t y of the t e s t population of b e e t l e s . The present researches have opened up two new p o s s i b i l i t i e s of e x p e r i mental s i t u a t i o n s f o r t e s t i n g o l f a c t o r y a t t r a c t a n t s f o r T. lineatum. upon the c e n t r i p e t a l response of b e e t l e s i n a f i e l d of odour. upon anemo-olfactory airstream.  One depends  The other depends  o r i e n t a t i o n and locomotion of b e e t l e s i n an odour-laden  Both have the advantage of a b r i e f e r p e r i o d of observation than  the  b o r i n g - i n response. The c e n t r i p e t a l response i s the one which i s c h a r a c t e r i z e d by the b e e t l e s repeatedly r e t r i e v i n g t h e i r p o s i t i o n w i t h i n a f i e l d of odour o r i g i n a t i n g i n the substratum,  This r e a c t i o n would serve the purposes of a bioassay t e c h -  nique i n which unknowns are introduced i n t o the substratum.  The l e n g t h of the  meandering path and/or the duration of contact w i t h the odour f i e l d would be compared w i t h values obtained w i t h the i n s e c t i n an odour-free f i e l d .  This  technique would have the economical feature of p e r m i t t i n g the u t i l i z a t i o n of both sexes f o r s t u d i e s of the primary  host a t t r a c t a n t . I t a l s o would y i e l d  information from specimens s t u d i e d i n d i v i d u a l l y .  Tracings of the path t r a v e l l e d  by a b e e t l e and/or the d u r a t i o n of contact w i t h the odour f i e l d provide  one  p o s s i b l e q u a n t i t a t i v e measure of a t t r a c t i v e n e s s . This study must be c a r r i e d  73  A  out either with flight-experienced beetles illuminated with a horizontal beam of light, or with non-flown beetles observed under a dark red light to which they are insensitive. The anemo-olfactory response would provide an immediate measure of attractiveness.  A test would depend upon directing an odour-laden airstream  toward flown or flight-experienced beetles i n the presence of an opposing illumination source, or toward non-flown beetles under a dark red light. The method would permit the utilization of both sexes when primary host attractants are to be studied. This method would be the least time-consuming of a l l . It i s conceivable that with this type of test, the manipulation of intensity of the opposing light source would provide a means f o r quantitative expression of olfactory attraction.  Strength of olfactory attraction would be measured  in terms of the strength of light necessary to inhibit the olfactory influence. In practice, however, the test might consist of the converse manipulation i n which the odour i s attenuated while the light i s kept constant.  CONCLUSIONS The present researches have cleared away some of the primary obstacles to a comprehensive understanding of the behaviour of T.  neatum (Oliv.).  In turn, the patterns of i t s behaviour assume importance i n terms of i t s biology and ecology. These studies have also removed the primary obstacles to the use of the insect as an instrument for bioassaying the attractant nature of chemical substances isolated from the host trees.  This laying  of foundations for bioassaying techniques also opens up opportunities for the study of factors affecting the formation of attractants i n wood i n as much as tests for attractancy w i l l no longer depend on the beetles boring into intact wood. Now i t should be possible to experiment with wood that i s i n a mechanically disintegrated  state, which i s more amenable to chemical  procedures. The following conclusions pertain to the pedestrian situation for the beetles i n their non-diapausing conditipn as they occur i n spring, prepared for normal emergence, f l i g h t and attack.  Males and females were  similar i n responses except i n those situations which involve boring into wood, as only the females perform this operation. 1. The beetles, before f l i g h t , are strongly photopositive at temperatures i n the range of 5° to 56°C. Positive phototactic response i s i n h i bited i n an increasing percentage of individuals at temperatures above 36°. At 58°C, positive response to light by the beetles ceases to exist. 2. The non-flown beetles react quickly to angular deviations of alignment i n respect to a light source  and turn with almost equal readiness  toward the light regardless of i t s angle. 3. The beetles' responses to light, before f l i g h t , may be c l a s s i f i e d as follows:  l ) not inhibited- the beetles immediately move or even 74  75 run toward the source of light; 2) i n i t i a l l y inhibited positive response^ the beetles may head away from light at the start of movement, but immediately turns about and move toward the source of light; 5.) inhibited positive response the beetles may or may not at the start of movement be inhibited by r  light but the general direction of movement toward the source of light i s oblique; and 4) completely inhibited  responser the beetles move with no  apparent response to light. 4 . The photopositive response largely masks the other potential capabilities of the non-flown beetles.  A photopositive response i s retained  regardless of the relative direction of light i n respect to the earth's gravitational f i e l d .  Its effect i s retained, albeit delayed, despite proxi-  mity of the insect to a host odour souroe. 5. Exclusion of the photic stimulus from flight-inexperienced beetles unmasks their capabilities of responding to host odour i n an odour f i e l d . 6 . Flight experience partially modifies the simple photic reaction of some individuals i n the absence of host odour, but the majority remain unchanged. 7. Flight experience prepares the beetles for a response to host factors i n the presence of light.  As brief a flight as five minutes has  produced this effect i n some individuals,  '/  8. A response to odour from attractive wood becomes manifest under various conditions: (a) Non-flown beetles display a response i n darkness i n the form of a "fluid" aggregation of part of a population free to move i n an area containing an odour f i e l d caused by either the presence of a piece of  _  ,.  ......  .  76  attractive wood or the introduction of a stream of a i r carrying attractive wood odour. (b) Plight-experienced beetles display a positive olfactory response under white light by lingering for an extended period of time over an odour f i e l d i n opposition to a beam of light. (c) Plight-experienced beetles display a positive olfactory response under white light by heading upstream i n a current of a i r carrying that odour i n opposition to a beam of l i g h t . (d) Hon-flown beetles display an inhibited olfactory response under white light but exhibit a positive olfactory response i n darkness. 9. Hon-flown and flight-experienced beetles take to flight i n the presence of a broad overhead f i e l d of light.  They do not take to  f l i g h t when light arrives from below the horizontal plane of vision of the beetles but they do so i n the presence of a combination of lights above and below. 10. As pedestrians, the beetles do not respond to patterns of black-and-white lines i n their immediate background as they do to a source of attractive wood odour.  This fact implies that vision i s not employed as  much as olfaction i n host-finding. 11. Non-flown beetles under pressure of 30 p s i do not respond to host odour while exposed to white light.  The implication i s that the presence  of gas bubble i n the ventriculus accumulated during f l i g h t does not produce the change of photic response i n the presence of odour by a pressure effect. This conclusion leaves the possibility of i t s acting by stimulating stretch receptors i n the gut wall. It also denies the experimenter this condition for studying olfactory responses i n non-flown beetles.  77 12. When odour already surrounds a beetle, the latter generally does not react to an airstream.  Some of the beetles which behave otherwise may  not have the threshold of response 15.  sufficiently lowered.  The responses of this insect to the conditions studied here  explain some of the important mechanisms of i t s ecology. The i n i t i a l strong positive response to light sponsors dispersal of the adult population in spring and empowers the insects with the capacity f o r t e r r i t o r i a l coverage. 14. The behaviour of Trypodendron i s not s t r i c t l y stereotyped i n the sense that i t follows a definite pattern.  While f l i g h t , f o r instance,  may be a normal conditioning or priming mechanism for the alighting or olfactory response, response to odour sources and the subsequent boring behaviour may be accomplished, i n the absence of previous f l i g h t experience, i n the dark. 15. The response of the flight-experienced beetle to an odourbearing airstream probably provides a simple mechanism f o r host discovery, i n which the host odour may act merely as a releaser of an anemotactic response.  This mechanism would lead the insect almost inevitably to the source  of the odour, without the necessity of one attributing to i t the memory i n a trial-and-error search, and without assuming the a b i l i t y of a three-mini meter insect to recognize direction i n an odour gradient which may extend over hundreds of meters.  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