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Some effects of host tree nutrition on establishment and survival of the balsam woolly aphid, Adelges… Carrow, Justin Roderick 1967

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i SOME EFFECTS OF HOST TREE NUTRITION ON ESTABLISHMENT AND SURVIVAL OF THE BALSAM WOOLLY APHID, ADELGES PICEAE (RATZ.) by J . RODERICK CARROW B.S.F., The University of Toronto, 1961 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science i n the Department of Zoology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1967 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag ree t h a t th;.o L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l no t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n , Depar tment o f The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8 , Canada i i ABSTRACT A greenhouse study was undertaken to investigate some relationships between n u t r i t i o n of the host tree, Abies amabilis, as influenced by s o i l f e r t i l i t y and n i t r o -gen f e r t i l i z e r s , and biology of the balsam woolly aphid, Adelges piceae (Ratz.). Seedlings were reared i n two s o i l regimes - nu t r i e n t - d e f i c i e n t mineral s o i l and enriched humic s o i l . A l l trees were inf e s t e d with aphid larvae, and obser-vations made to determine the influence of s o i l f e r t i l i t y on the establishment rate of larvae on host trees. Subsequently, groups of 10 trees were treated with f o l i a r nutrients, using ammonium n i t r a t e and urea i n various concentrations. The establishment rate of larvae on humic s o i l host trees was 2.5> times greater than on mineral s o i l trees. In addition, growth rate of the aphid population on humic s o i l trees was 31% greater than on mineral s o i l trees over a four week period. S o i l f e r t i l i t y also influenced the l i f e h i s t o r y of the i n s e c t . One f o l i a r nutrient adversely affected the aphid population. Over a 10 week period, the aphid popula-t i o n on trees treated with Vfo ammonium n i t r a t e decreased by Z3%» whereas the control population Increased 30.9$« It i s postulated that t h i s f o l i a r treatment manifests i t s adverse eff e c t p r i m a r i l y by i n h i b i t i n g i n i t i a l s e t t l i n g of larvae on the host trees. This i n h i b i t i o n may be rela t e d to f e r t i l i z e r -Induced alterations i n the amino acid composition of feed-ing t i s s u e . Supervisor i i i TABLE OP CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OP CONTENTS i i i TABLES v FIGURES v i ACKNOWLEDGEMENTS v i i INTRODUCTION 1 MATERIALS AND METHODS k 1. The Insect ij. 2. The Host Tree . . 6 3. Guiding P r i n c i p l e s i n Host Tree N u t r i t i o n . . 7 li. Establishment and Growth of the Host Tree Population . . . . . . . . . . . 8 5>. Infestation of Host Trees with Balsam Woolly Aphid 10 6. Study of the Aphid Population 12 7. F o l i a r F e r t i l i z a t i o n of Host Trees . . . . . 13 8. Analysis of Bark Tissue 16 9. S t a t i s t i c a l Analysis 17 RESULTS 18 1. Response of Host Trees to Growing Conditions. 18 2. Infestation of Host Trees 19 3. Study of the Aphid Population 21 If.. E f f e c t s of F o l i a r F e r t i l i z a t i o n 2$ i v 5>.. S t a t i s t i c a l A n a l y s i s 31 6. A n a l y s i s o f B a r k T i s s u e 33 DISCUSS ION . 3h 1 . R e a r i n g o f H o s t T r e e s and A p h i d s . . . . . . 31+ 2 . T r e e N u t r i t i o n and B i o l o g y o f t h e A p h i d . . . 38 3 . F o l i a r F e r t i l i z a t i o n and i t s E f f e c t o n t h e I n s e c t kl i i . Am ino A c i d C o m p o s i t i o n o f H o s t T i s s u e . . . . 62 F u t u r e I n v e s t i g a t i o n 63 SUMMARY AND CONCLUSIONS 66 L ITERATURE C I T E D 68 • V TABLES Number T i t l e Page I Fecundity and duration of l i f e stages of aphids reared on host trees growing on mineral s o i l and humic s o i l (mean values). . . 2l\. II Fecundity and duration of l i f e stages of aphids on two f i e l d p l o t s In the Vancouver area. 25 I I I V a r i a t i o n i n aphid population l e v e l s (mean no. aphids/tree) over the 10rweek period following i n i t i a l treatment xtfith f o l i a r nutrients 27 IV V a r i a t i o n i n aphid population l e v e l s on host trees growing on both s o i l types over the 10 week period following i n i t i a l treatment with f o l i a r nutrients 32 V Concentrations of ammonia and major free amino acids i n bark tissue from humic s o i l trees which received control and 1% ammonium n i t r a t e treatments 33 v i FIGURES Number T i t l e Page 1 Experimental plan 11 2 Rate of i n i t i a l establishment and population growth of aphids on mineral s o i l trees and humic s o i l t r e e s . . 22 3 Changes i n population l e v e l s of f i r s t i n s t a r aphids on host trees (both s o i l s ) treated with f o l i a r nutrients. • • 28 1L Changes i n t o t a l population l e v e l s of aphids on host trees (both s o i l s ) treated with f o l i a r nutrients 29 5> Comparison of the e f f e c t s of 1% ammonium n i t r a t e treatment on f i r s t i n s t a r population and t o t a l population of balsam woolly aphid. . 30 v i i ACKNOWLEDGEMENTS The \*rlter wishes to express his appreciation f o r the advice and in t e r e s t shown by the members of his committee, Doctors A. Kozak, V.J. Krajina, P.A. Larkin, and D.P. Ormrod. Special gratitude i s expressed to my supervisor, Dr. K. Graham, f o r h i s cooperation and i n t e r e s t , and e s p e c i a l l y f o r suggesting what proved to be a very i n t e r e s t i n g area of research. The assistance of Dr. Kozak In s t a t i s t i c a l analysis of the data i s greatly appreciated. Credit i s also due my wife, who offered constant i n t e r e s t , enthusiasm, and assistance throughout the study. Acknowledgement i s made to the University of B r i t i s h Columbia f o r use of educational, laboratory, and greenhouse f a c i l i t i e s . INTRODUCTION This study was i n i t i a t e d to investigate some ef f e c t s of tree n u t r i t i o n on the i n t e r a c t i o n betoken balsam woolly aphid, Adelges piceae (Ratz.), and i t s host tree, the true f i r , (Abies spp»). More s p e c i f i c a l l y , i t i s desiied to know the effe c t of host n u t r i t i o n , e s p e c i a l l y as influenced by chemical f e r t i l i z a t i o n , on establishment and su r v i v a l of the insect, as well as sur v i v a l capacity of the trees. The immediate study i s concerned p r i m a r i l y with the former, namely, the ef f e c t s on the i n s e c t . Variations i n the n u t r i t i o n a l status of a host organism may have an influence upon the parasite which i t nourishes, as well as upon i t s own reaction to attack. I t should be possible therefore, to manipulate strength of the host-parasite i n t e r -action by imposing changes on the n u t r i t i o n a l status of the host. The p o s s i b i l i t y of thus modifying interactions between insects and t h e i r hosts i s of po t e n t i a l i n t e r e s t to entomologists who wish to understand t h i s facet of nature, as well as to those who wish to manipulate i t . The importance of n u t r i t i o n a l balance i n insect diets i s emphasized by House (1966a) In his " p r i n c i p l e of nutrient pro-p o r t i o n a l i t y " . This p r i n c i p l e states that metabolically suitable proportions of nutrients are needed f o r normal n u t r i t i o n . House (1965, 1966b) showed by experiment that n u t r i t i o n and e f f i c i e n t food u t i l i z a t i o n were not affected by concentration of t o t a l nutrients i n a food, provided the r a t i o of nutrients was 2 s a t i s f a c t o r y . He c i t e s Rodriguez ( i 9 6 0 ) , who showed that f e r t -i l i z e r s can change the composition of plants quantitatively, and consequently, t h e i r n u t r i t i o n a l value for insects, some-times s e l e c t i v e l y . In addition, House (19&5) suggested that n u t r i t i o n a l imbalances i n the host may reduce po t e n t i a l destruct-iveness of an insect population. He has even ventured the pro-posal that protection from insect attack could be afforded some materials by a l t e r i n g t h e i r composition i n such a way that the supply of nutrients would have injurious effects on the insect (House 1 9 6 6 a ) . However, no one has e x p l i c i t l y suggested that a l t e r a t i o n of the nutrient composition of host t i s s u e , through addition of f e r t i l i z e r s , might be used to control phytophagous insects, either by inducing a phagoinhibitory mechanism, or by rendering the host tiss u e t o x i c to feeding i n s e c t s . Available information on the effects of plant n u t r i t i o n on insects applies p r i n c i p a l l y to responses manifested by insect populations, without providing a clear analysis of functions affected i n the i n s e c t . Stark (1965) reviewed recent observa-tions on the influence of fo r e s t f e r t i l i z a t i o n on populations of i n s e c t s . Most observations were only i n c i d e n t a l to s i l v i -c u l t u r a l studies f o r which f e r t i l i z e r applications were made, and were not an outcome of s p e c i f i c attempts to manipulate insect populations. However, numerous instances are c i t e d of s i g n i f i c a n t reduction of insect populations following applica-t i o n of f e r t i l i z e r s , most frequently nitrogen compounds. 3 In r e l a t i o n to Adelges, Herker (I960, 19^1, 1962) reported that addition of some nitrogen compounds to fo r e s t stands resulted i n increased l a r v a l m o r tality of Adelges (Dreyfusia) n u s s l i n i . In a more s p e c i f i c study, Johansson (1961t) demonstrated that a l t e r a t i o n of the nitrogen l e v e l i n the host plant depressed reproduction of aphids. Mineral d e f i c -iencies disturbed yolk synthesis i n many insects and resulted i n decreased fecundity. However, some reports (Merker 1961, Mustanoja and Leaf 1965) suggest that i n certa i n cases, addi-t i o n of mineral f e r t i l i z e r s to conifers, while causing reduc-t i o n i n the population of d e f o l i a t o r s , simultaneously resulted i n an increased reproductive rate i n Aphis spp. Some uncertainty about the re l a t i o n s h i p betoeen sever-i t y of insect attack, s i t e q u a l i t y , and host vigour s t i l l e x i s t s . Varty land Johnson et_ a l (1963) suggest that more severe i n f e s t -ations of balsam woolly aphid are associated with a high s i t e index and trees of dominant and co-dominant crown classes, while i n a g r i c u l t u r a l entomology, a commonly held opinion i s that crops growing on l e s s f e r t i l e s i t e s are l e s s vigorous and there-fore, more susceptible to insect i n f e s t a t i o n . 1. I.W.Varty, personal communication k MATERIALS AND METHODS 1. The Insect In h i s 1952 p u b l i c a t i o n on the biology of balsam woolly aphid i n the Maritime region, Balch gives a complete description of l i f e h i s t o r y . However, some var i a t i o n s i n l i f e h i s t o r y have been noted i n the P a c i f i c Northwest (Johnson and Wright 1957, Harris 1965)* The adult i s a purple black, oval insect l e s s than one mm. long, e n t i r e l y secluded under a secretion of white waxy threads or "wool". No males or winged forms have been i d e n t i f i e d i n t h i s region; a l l mature adults are parthenogenetic females, and thus are capable of producing s e l f - f e r t i l e eggs. Within a few days a f t e r reaching adulthood, o v i p o s i t i o n begins at rates which vary considerably between and within regions. A c l u s t e r of oval amber-coloured eggs can be observed amongst the threads of waxy wool. The amber-coloured l a r v a which emerges from the egg i s 0.5 ram. or l e s s i n length, and because i t i s the only motile stage, i s commonly referred to as the "crawler". (Crawlers are r e a d i l y carried by a i r currents, and consequently, d i s p e r s a l of an aphid population i s effected p r i m a r i l y by winds.) The crawler usually wanders about on the bark u n t i l a feeding s i t e has been selected. I t then i n s e r t s i t s stylets,..and enters diapause f o r several weeks, the duration of which depends on c l i m a t i c conditions and elevation. This i s the f i r s t i n s t a r stage, or "neosistens". C h a r a c t e r i s t i c a l l y , the aphid remains s e s s i l e at t h i s feeding s i t e u n t i l death. Upon emerging from diapause, the aphid progresses through second and t h i r d i n s t a r stages, and becomes an adult. Between each of the four stages, moulting occurs. Depending on l a t i t u d e and elevation, the number of generations i n one year varies from two to four (Mitchell et a l I96I). Populations at higher elevations i n the P a c i f i c North-west ^S^OO'-lf-GOO') u s u a l l y produce two generations per year, those at intermediate elevations ( 1 0 0 0 ' ) have three generations, and those at low elevations ( 2 3 0 1 ) go through three to four generations annually. In each summer generation, the neosistens exhibits a summer diapause; thus, these are termed S a e s t i v o s i s t e n s " generations. In general, the winter population, the "hiemosistens" generation, Includes only neosistentes, since a l l . other stages die o f f . However, recently i t has been suggested that a consid-erable portion of populations i n the coastal region may over-winter as second or t h i r d i n s t a r stages, owing to the more moderate winter climate (Greeribank 1 9 6 3 ) * A c t i v i t y i s resumed early i n the spring by the neosistens, and i t i s f i r s t indicated by a swelling of the body, and appearance of a drop of "honeydew" a t the p o s t e r i o r end. On a heavily infested grand f i r on the Univ e r s i t y of B.C. campus, which was used as a source of aphids f o r experimental work, the hiemosistens generation was short. Crawlers from the aestivosistens generation were s t i l l apparent on the bark on Dec. li|.th, and by March 3 r d , many overwintering neosistentes had formed drops of honeydew, and resumed feeding. 6 2. The Host Tree Trees infested with balsam x-roolly aphid usually suffer serious damage. I t i s thought that the feeding aphid i n j e c t s some substance, as yet u n i d e n t i f i e d , into host t i s s u e v i a the s t y l e t s (Balch jet a l I96J4.). This substance may promote abnormal a c t i v i t y of a substance already i n the tree, by enzymatic or sy n e r g i s t i c action. In trees of pole s i z e , or l a r g e r , feeding apparently takes place i n e x t r a c e l l u l a r spaces of the c o r t i c a l parenchyma (Balch 193>2). In younger trees, the feeding s i t e may be the phloem, since s t y l e t s are long enough to extend about 1.5 v:«. into the bark. Injection of t h i s substance into the tree e l i c i t s a s p e c i f i c growth response from the host, by disturbing the normal balance of growth-regulating substances i n the tree. I f i n f e s t a t i o n occurs i n the peripheral portion of the crown, t h i s abnormal growth pattern i s manifested as "gouting" - the formation of swellings by twigs, due to c e l l -u l a r hypertrophy. A stem attack also results i n an a t y p i c a l growth pattern. Abnormally wide annual rings .of very dense, reddish wood - termed "rotholz" - are formed. In both types of attack, the growth response i s such that the tree's vascular system i s severely impaired (Oechssler 19&2). Crown attack alone may r e s u l t i n repeated suppression of the current year's f o l i a g e . I f the attack i s prolonged, the tree usually i s s e r i -ously weakened or k i l l e d . Stem attacks, because they i n t e r f e r e with the main conduction system, greatly decrease translocation, and death of the tree follows quickly. 7 Although any Abies spp. could be used f o r experimental study, A. amabilis - known as balsam f i r , P a c i f i c s i l v e r f i r , or amabilis f i r - has several advantages as a host species. Hot the l e a s t of these i s i t s economic value. According to Johnson e_t a l (1963), destruction of balsam f i r stands repre-sents a greater economic loss than destruction of any of the other true f i r s . Prom an experimental standpoint, A. lasiocarpa i s most e a s i l y i n f e s t e d with balsam woolly aphid, and maintains populations better than other Abiesl However, i t i s more d i f f -i c u l t to c u l t i v a t e i n the greenhouse. A. grandis grows well i n the greenhouse, but r e s i s t s i n f e s t a t i o n with woolly aphid more than other f i r s 1 . A. amabilis represents a compromise, since i t grows s u f f i c i e n t l y w e ll under greenhouse conditions, i s not r e s i s t a n t to i n f e s t a t i o n , and maintains aphid populations successfully. In the P a c i f i c Northwest, A. amabilis i s found i n the coastal western hemlock and mountain hemlock forest zones, which are characterized by annual p r e c i p i t a t i o n of over 100 inches, and by thick deposits of mor humus (Krajina 196£). 3. Guiding P r i n c i p l e s i n Host Tree N u t r i t i o n In choosing a culture method f o r host trees, two tech-niques were considered - natural s o i l s bf d i f f e r e n t f e r t i l i t i e s , and sand culture, i n which nutrient solutions of s p e c i f i c comp-osi t i o n s are supplied to the trees. 1. H.E. Johnson, personal communication 2. V.J. Krajina, personal communication 8 This study was designed to investigate several general relationships between host n u t r i t i o n and the insect, with the immediate goal of determining which aspects, i f any, warranted more intensive study i n the future. One aim was to test whether gross differences i n nutrient supply to the tree would exert any e f f e c t on the insect population and the tree's resistance to attack. Another aim was to determine whether the effects of f e r t i l i z e r s on insects would be influenced by such d i f f e r -ences i n s o i l f e r t i l i t y . Any i n v e s t i g a t i o n of effects of f e r t -i l i z a t i o n i s e s s e n t i a l l y a study of e f f e c t s of nutrient supple-ments. However, sand culture i s u s u a l l y employed i n studies of e f f e c t s of nutrient d e f i c i e n c i e s on plants. It was decided that a highly regulated method, such, as sand culture, was not necessary to gain s i g n i f i c a n t Information about general r e l a -tionships between s o i l f e r t i l i t y , f e r t i l i z a t i o n , and the Insect. For these reasons, natural s o i l was chosen as the medium f o r host tree culture. 4. Establishment and Growth of the Host Tree Population Host trees were selected from a stock of four year o l d seedlings of balsam f i r , Abies amabilis, supplied by the B r i t i s h Columbia Forest Service. The provenance of the seedlings i s : 1 Location: Block 75» Cowichan Lake Elevation: 2800 f t . C o l l e c t i o n Date: 1959 1. N.E.Sjoberg, B.C. Forest Service 9 Prom t h i s stock, lf?0 trees exh i b i t i n g well-developed roots, normal tops, and good leader growth, were selected. These trees were potted, using glazed clay pots and two s o i l regimes* Half the trees were planted i n mineral s o i l obtained on the University of B,C. campus, and the other h a l f i n humic green-house potting s o i l . Analysis of the two s o i l s , using Morgan's method (described i n Morgan 19l}.l), revealed that the mineral s o i l was medium low i n n i t r a t e , and low i n potassium and c a l -cium, while the humic s o i l was very high i n n i t r a t e and potas-1 sium, and high i n calcium. To break dormancy, the trees x^ere kept outside f o r a 2i| 1 day period, beginning Nov. 23rd. They were then moved into the greenhouse, and exposed to a temperature range of 60 to 70°P. and a 15 hour photoperiod. Temperatures were recorded with a thermograph. The date on *ihich each tree exhibited fl u s h i n g of new growth was recorded. These temperature-photoperiod condi-tions were maintained u n t i l early May, when the l i g h t s were shut o f f , and the trees exposed to the natural photoperiod. To prevent high temperatures, the greenhouse was whitexirashed, and a s l a t screen erected over the trees, with the r e s u l t that summer temperatures ranged between 65 and 85°P. About mid-Sept-ember, an a r t i f i c i a l 16 hour photoperiod was established to i n h i b i t onset of dormancy i n the trees. The s l a t screen was removed, and temperatures were maintained betx^een 65 and 75°F» throughout the f a l l . Second flushes of new growth were recorded. 1. V.J.Krajina, personal communication. 2. Analysis by B.Spindler, Dept. of S o i l Science, Univ. of B.C.. 3. E.B.Tregunna, personal communication. 10 Throughout the whole growing season, trees were watered two or three times weekly with d i s t i l l e d water. !?• Infestation of Host Trees with Balsam Woolly Aphid Prom the lf?0 potted trees, 60. trees exhibiting the best growth were selected f o r i n f e s t a t i o n . Of these, 30 were grow-ing i n mineral s o i l and 30 i n humic s o i l (Pig.l) . A l l needles xrere removed from the main stem of each tree up to the top l a t e r a l s , and plasticene c o l l a r s were applied to the base of each branch and to the top of the main stem to define the area of observation on each tree. A l i g h t covering of absorbent cotton was placed around the upper part of the main stem, to 1 encourage s e t t l i n g of aphids. The source of aphids was pieces of bark from the underside of branches of an infe s t e d grand f i r , Abies grandis, on the campus. These bark pieces were examined microscopically to ensure that large numbers of eggs and crawlers were present. They were then subdivided into pieces about $ mm. x 20ram., placed near the base of the main stem with the outer surface against the tree, and t i e d t i g h t l y with black thread. In mid-December, the trees were infe s t e d as described and establishment resulted, but the aphid population was l o s t about two months l a t e r . Another attempt was made A p r i l 23rd, using bark pieces with very few crawlers, but large numbers of eggs. V i r t u a l l y no establishment resulted i n t h i s case. In mid-June, a t h i r d attempt was made, using two bark pieces 1. N.E.Johnson, personal communication. 30 trees on mineral s o i l , a l l Infested 60 trees, experimental stock 5> trees 1.0% HH 4I0 3 5> trees 0.3$ BH4N03 5> trees 1*5$ urea 5> trees 1.0$ urea 5> trees 0.5$ urea 5 trees control 30 trees on numic s o i l , a l l Infested 5> trees 1.0$ NH4N03 5> trees 0.3$ NH4N03 5 trees 1.5$ urea f? trees 1.0$ urea % trees 0»-5$ urea 5 trees control P i g . l . Experimental plan 12 with a minimum of li). crawlers and iiO eggs f o r each tr e e . These pieces were randomly selected from a large supply of infested bark, to avoid exposing one segment of the tree population to more aphids than another segment. Trees were checked weekly, and those with small aphid populations (less than 10) were re-inf e s t e d with f r e s h bark pieces. When i n f e s t a t i o n of the trees had been attained, the bark pieces were removed. In addition, four trees were infested using bark pieces containing no crawlers, but 30-35 eggs per tree. These trees were examined d a i l y to determine success of establishment. 6. Study of the Aphid Population (a) I n i t i a l establishment rate and population growth At Intervals of 7-10 days a f t e r i n i t i a l i n f e s t a -t i o n , aphid populations on each tree were counted, using a 15X magnifier and microscope l i g h t . Within the observation area on each tree, the numbers of each l i f e stage were recorded. These stages were: crawler - amber-coloured motile l a r v a with no wool; i n s t a r I (neosistens) - s e t t l e d , i n diapause; immature adult (instars II and I I I ) ; and adult - egg-producing stage (Greenbank 1963). (b) L i f e h i s t o r y study Prom each s o i l regime, s i x trees were randomly selected* f o r more det a i l e d study of the aphid l i f e h i s t o r y . On each of the 12 trees, small groups of aphids were marked 1; Trees were assigned code numbers, and 12 numbers were selected. 13 o f f , using coloured p e n c i l . With the aid of quadrant mapping, observations were, made at le a s t once a week, beginning July 22|th. These observations included: l o c a t i o n of each aphid; l i f e stage - i . e . crawler, newly s e t t l e d crawler, neosistens (instar I ) , i n s t a r I I , i n s t a r I I I , adult; and the number of eggs v i s i b l e on each adult. Movement of aphids away from feed-ing;; s i t e s was noted. The t o t a l population within the observa-t i o n areas on these 12 trees ranged from 60 to 100 during the study. In addition, a l i m i t e d study was i n i t i a t e d August 15"th to compare fecundity of adults reared on mineral s o i l trees and humic s o i l t rees. Prom the aphid population compris-ing the l i f e h i s t o r y study, s i x adults on trees from each s o i l type were chosen, and at each observation, a l l eggs were removed from each adult, using a dissecting needle and camel h a i r brush. The l i f e h i s t o r y study was continued u n t i l October 2 1 s t . 7» F o l i a r F e r t i l i z a t i o n of Host Trees (a) Composition of treatments S o i l s of the P a c i f i c Northwest forests are generally d e f i c i e n t i n nitrogen (Mustanoja and Leaf 1 9 6 5 ) , and i n nature, balsam f i r exhibits a s t r i k i n g response to nitrogen f e r t i l i z e r s ) For t h i s reason, as well as those previously mentioned (pp. 2 , 3 ) , t h i s portion of the study was confined to e f f e c t s of nitrogen 1. S.P.G-essel, personal communication. 14 f e r t i l i z e r s only. F o l i a r a p p l i c a t i o n was used f o r two reasons. F i r s t , uptake of f o l i a r nitrogen i s very f a s t , with maximum absorption occurring within 48 hours of spraying (Wittwer and Tukey 1957, Shibamoto et a l 1 9 6 0 a ) . This feature f a c i l i t a t e s study of the effects of nutrients on the trees and aphids. Second, t h i s method provides a d i r e c t means of assessing effects of f e r t i l i z e r s , since influences of s o i l chemistry and micro -organisms on nutrient uptake by the tree are eliminated (Boynton 1 9 5 4 ) • The nitrogen f e r t i l i z e r s chosen were urea and ammon-ium n i t r a t e . Although urea has not been reported to af f e c t f o r e s t i n s e c t s , i t i s one of the most commonly used nitrogen f e r t i l i z e r s (Boynton;- 1954* Shibamoto et a l 1960a, Mustanoja and Leaf 1965, Hagner et a l 1966) . Within the P a c i f i c Northwest, several workers have used urea i n forest f e r t i l i z a t i o n t r i a l s (Gallagher 1964, Beaton et a l 1965, M i l l e r and Szarmes). With such universal popularity, i t was desirable to assess the effects of urea applications on balsam woolly aphid. Another commonly used nitrogen f e r t i l i z e r i s ammon-ium n i t r a t e (Kramer and Kozlowski I960, Gallagher 1964, M i l l e r and Szarmes). Besides being one of the cheapest nitrogen car-r i e r s (Mustanoja and Leaf 1 9 6 5 ) , Merker (1961) reports that a p p l i c a t i o n of ammonium n i t r a t e to host trees was accompanied by increased l a r v a l mortality i n Adelges (Dreyfusia) n u s s l i n i . Six f o l i a r treatments were applied to infested trees. Urea was used i n three concentrations - 0 . 5 $ (Boynton 1954, Shibamoto et a l 1 9 6 0 b ) , 1 . 0 $ and 1 .5$ ( M i l l e r and Szarmes). Ammonium n i t r a t e was applied i n concentrations of 0.3$ (M i l l e r and Szarmes), and 1 . 0 $ • The control treatment was d i s t i l l e d water. Urea and ammonium n i t r a t e solutions were made up with d i s t i l l e d water, and a wetting agent - poly-ethylene g l y c o l liOO mono-oleate - was added to a l l s i x t r e a t -ments at a concentration of 1 : 2 0 0 0 (Boynton 19%k)• (b) Application of spray Prom the populations of 30 trees growing on each 1 s o i l , s i x groups of f i v e trees each were randomly chosen. Each group received a d i f f e r e n t f o l i a r treatment ( F i g . l ) . To f a c i l i t a t e spraying, each tree was placed on a rot a t i n g platform. Acetate shields were used to cover the exposed sur-face of s o i l i n the pot ; and the tree stem supporting the aphid population. A l l trees were sprayed to dri p point with 1 the appropriate solution, using a hand atomizer. The concen-trations of various nutrients on the needles at drip point were calculated to be: 0.5$ urea - 2 . 1 ^ x 1 0 4 gm.urea/sq.cm. needle surface 1 . 0 $ urea - i i.30 x 1 0 " 4 gm.urea/sq.cm. needle surface 1.5$ urea - 6.l{.5 x 1 0 " 4 gm.urea/sq.cm. needle surface 0.3$ NH^NOj - 1 . 2 9 x 1 0 " 4 gm.NH4Er03/sq.cm. needle surface 1 . 0 $ NH^KOj - !j..30 x 1 0 " 4 gm.NH4H03/sq.cm. needle surface Special care was taken to ensure that no spray contacted aphids d i r e c t l y . Excess spray was allowed to drip o f f before 1 . Trees were assigned code numbers, and l o t s selected f o r each treatment. 2 . D.Ormrod, personal communication. 16 removing the acetate s h i e l d s . A l l s i x treatments were applied i n i t i a l l y i n the period from Sept. 19th to 28th, and again i n the period from Oct. 7 t h to lij.th. Thereafter, the control and 1% ammonium n i t r a t e treatments were applied on Nov. 7 t h (Shibamoto et a l 1960b). (c) Observation of the aphid population and trees Immediately before the f i r s t treatment was applied, a population count was made on each tree, noting the numbers of each stage within the observation area. Subsequent counts were made just before trees were given repeat applications of nutrient treatments. In addition, conditions of the trees were noted at each observation, with p a r t i c u l a r attention fe© condition of the needles and date of bud f l u s h i n g . 8. Analysis of Bark Tissue Kramer and Kozlowski (i960) state that most of the n i t -rogen i n xylem sap of conifers occurs as free amino acids and amides, p a r t i c u l a r l y glutamine, asparagine, glutamic a d d , and aspartic a c i d . This amino acid-amide complement i n tree sap i s also reported by B o l l a r d (1958), and by M i t t l e r (1953, 1958), i n h i s studies of the composition of phloem sap i n -gested by the willow aphid, Tuberolachnus salignus. Several workers (McBeath et a l i 9 6 0 , Harris and vonLoesecke i960) have reported that although nitrogen f e r t i l i z a t i o n of v a r i -ous g r a i n crops r e s u l t s i n elevated protein content, q u a l i t y 17 of the protein may be decreased due to an induced amino. acid imbalance* In l i g h t of the foregoing considerations, bark t i s s u e was c o l l e c t e d from a l l humic s o i l trees which had received the control treatment and 1$ ammonium n i t r a t e treatment. A one gram bark sample from each of the two treatments was selected and free amino acids were extracted with 95$ ethanol. This extract tjas centrifuged and dried, and then analysed f o r free amino acids using a Technicon autoanalyser. 9» S t a t i s t i c a l Analysis Analysis was complicated by the fact that i n i t i a l pop-u l a t i o n l e v e l s of aphids p r i o r to treatment d i f f e r e d consid-erably among the various treatment groups. Accordingly, the data were analysed using covariance techniques, with "x" the number of aphids p r i o r to treatment, and "y" the number at any p a r t i c u l a r time a f t e r i n i t i a l treatment. Thus a l l com-panions were on means adjusted f o r i n i t i a l differences i n population s i z e . The significance of difference between these mean values at each time i n t e r v a l was assessed, using the 1 i l . s . d . and Dunnett's procedure (Steel and Torrie i 9 6 0 ) . 1. A. Kozak, Faculty of Forestry, Univ. of B.C. 2. F.A. Larkin, I n s t i t u t e of F i s h e r i e s , Univ. of B.C 18 RESULTS 1. Response of Host Trees to Growing Conditions (a) Greenhouse conditions Approximately one month af t e r the trees were moved into the greenhouse and exposed to a long photoperiod and high temperatures, terminal buds of some trees turned l i g h t green and became swollen. Bud f l u s h i n g started January li}.th, and during the following f i v e weeks, new growth was observed on a l l trees. No difference i n f l u s h i n g date could be observed between trees on humic s o i l and those on mineral s o i l . Of trees growing on humic s o i l , two exhibited no f l u s h i n g of main stem terminal buds, and branch buds of one tree did not f l u s h . Main stem terminal buds of f i v e mineral s o i l trees d i d not f l u s h , but branch buds of a l l trees formed new growth. The autumn f l u s h of growth began October 20th -about one month a f t e r trees had been exposed to a longer photoperiod and higher temperatures - and flushing continued over a seven week period i n various trees.However, t h i s f l u s h was not uniform; eight of the 30 mineral s o i l trees, and 11 of the 30 humic s o i l trees formed no new growth. This incon-sistency i n developing secondary growth could not be related to severity of aphid i n f e s t a t i o n on the trees. 19 (b) S o i l conditions New growth formed by trees on mineral s o i l was quite short, whereas new growth on humic s o i l trees was much longer, and lusher In appearance. The growth pattern of trees growing oh humic s o i l was s a t i s f a c t o r y f o r the purposes of t h i s study. However, the growth pattern of mineral s o i l trees could not be termed anything but poor. (c) Response to aphid i n f e s t a t i o n Six weeks a f t e r the trees were I n i t i a l l y exposed to crawlers, gouting was noted on terminal buds of branches on two tr e e s . After 22 weeks of i n f e s t a t i o n , severe gouting had developed on 11 trees, nine of which were growing on humic s o i l . Gouting took the form of noticeable swelling of the main stem or terminal bud region, and was always assoc-iated with a group of s e t t l e d aphids. Of the trees which exhibited gouting, only two supported populations of l e s s than 100 aphids. The other nine had very heavy i n f e s t a t i o n s , ranging from 101 to 328 aphids per t r e e . 2. Infestation of Host Trees (a) Exploratory behaviour of crawlers The rate of movement of crawlers from bark pieces, used f o r i n f e s t a t i o n , onto the host trees was varied. Some moved onto the stem within a few minutes; others remained on the bark piece f o r as long as seven hours. Once on the 20 main stem, they exhibited a strong photopositive reaction, moving tip the stem to the c o l l a r . They then began explora-tory probes into the bark with t h e i r s t y l e t s . Throughout t h i s period of exploration, crawlers were frequently observed moving back down the stem. On a few test trees, with no plasticene c o l l a r s to confine the aphids, crawlers moved to the t i p s of the branches and main stem, so that the population tended to concentrate around the periphery of the crown. (b) S e t t l i n g of crawlers Crawlers xtfhich inserted t h e i r s t y l e t s and remained on the trees were concentrated on the upper main stem, under the absorbent cotton, or under bark pieces used to i n f e s t the tr e e s . There was also obvious c l u s t e r i n g , r e s u l t i n g i n uneven dispersal of aphids over the stem surface. In most cases, the crawlers s e t t l e d i n groups of f i v e or more, with less than a bodylength between i n d i v i d u a l aphids. Many groups were located on or adjacent to needle scars. During the four day period a f t e r s e t t l i n g , the colour of the neo-sistens changed from l i g h t amber to dark amber to dark purple, and a wax f r i n g e formed along the mid-dorsal l i n e , interseg-mental membranes, and around the margin of the dorsum. In nature, the majority of s e t t l e d neosistentes apparently remain stationary throughout the remainder of the l i f e cycle. However, the neosistentes which s e t t l e d a f t e r i n i t i a l i n f e s -t a t i o n i n mid-December abandoned the host trees within two 21 months. Very few corpses were found j apparently, the aphids withdrew t h e i r s t y l e t s and departed from the host trees. (c) Infestation with eggs On the four trees which were exposed to bark pieces with eggs, but no crawlers, observation over a one week period revealed that there had been no s e t t l i n g of crawlers on the host trees. In the meantime, a l l the eggs had hatched. 3. Study of the Aphid Population (a) A r t i f i c i a l population establishment Counts made over the 18 day period a f t e r trees were exposed to aphids i n mid-June showed that the l e v e l of neosistens establishment was considerably greater on humic s o i l trees than on mineral s o i l trees (Pig.2). At the end of that period, the mean number of aphids per mineral s o i l tree was lli«8 + 11.4 (mean + 2s), while the mean number of aphids per humic s o i l tree was 36.8 + 20.2. (b) Growth of aphid population Prom July 7th to August 20th, a period of approx-imately s i x weeks, the mean population of aphids per tree remained r e l a t i v e l y constant (Pig.2). A f t e r August 20th, the aphid population on a l l tree>s exhibited an increase, with the. rate of Increase on humic s o i l trees being greater-20 30 IO 20 30 9 19 29 8 18 28 June July August 5eptember F i g . l . RATE OF INITIAL ESTABLISHMENT AND POPULATION 6R0WTM OF APHIDS ON MINERAL 501L Tfc&ES AND HUMIC SOIL TREES . 23 During the l a s t month of observation, the aphid population on humic s o i l trees increased by 137$, whereas the popula-t i o n on mineral s o i l trees increased by 1 0 0 $ . Concurrently, the r a t i o of the mean number of aphids per humic s o i l tree to the mean number of aphids per mineral s o i l tree increased from 2 .55 to 2 .90 ( P i g . 2 ) . The aphid population established on the trees i n June, was maintained u n t i l experimentation was terminated about December 1 s t . At that time, f i r s t i n s t a r aphids present represented the beginning of the fourth successive genera-t i o n on the host trees. During l a t e November, a noticeable decline i n ov i p o s i t i o n occurred. (c) L i f e h i s t o r y Detailed study of the l i f e h i s t o r y resulted i n several i n t e r e s t i n g observations. Although the aphid char-a c t e r i s t i c a l l y remains s e t t l e d at one feeding s i t e through-out the l i f e cycle (Balch 1952, Varty 195&), many instances of movement were noted. Within the scope of t h i s l i m i t e d l i f e h i s t o r y study, moves by 22 aphids were recorded. As weH, many additional aphids exhibited movement on other t r e e s . These moves took the form of withdrawing the s t y l e t s completely, walking across the bark surface, and either attempting to r e i n s e r t the s t y l e t s at some new feeding s i t e * or abandoning the host t r e e . Moves were exhibited by a l l immature stages. The neosistens moved either shortly a f t e r 2h i n i t i a l s e t t l i n g or at the end of i t s diapause, while moult-ing into the second i n s t a r stage. Occasionally, second and t h i r d i n s t a r aphids moved while moulting into the next l i f e stage. Evidence f o r these moves was cast skins l e f t be-hind at the o r i g i n a l feeding s i t e s . M o rtality among immature stages was l i g h t . How-ever, several dead aphids were noted i n the l i f e h i s t o r y study. In nearly a l l cases of juvenile mortality, the aphid was observed withdrawing i t s s t y l e t s from the bark shortly before death. T y p i c a l l y , dead aphids were black, with t h e i r s t y l e t s p a r t i a l l y withdrawn. Results of observations made to compare fecund-i t y and duration of various l i f e stages In aphids reared on host trees on both s o i l regimes are presented i n Table I. Table I . Fecundity and duration of l i f e stages of aphids reared on host trees growing on mineral s o i l and humic s o i l (mean values). No. of aphids observed Mineral s o i l trees Humic s o i l trees i n s t a r I 1 s t generation 110 6 . 0 weeks 5 . 0 weeks 2nd and 3 r d generations 18 7.7 " 7.5 " i n s t a r II 27 3 days 3 days i n s t a r I I I 21 3 " 3 » adult 2k 6.1 weeks i|..2 weeks fecundity eggs/adult/week 12 2.58 2.62 2$ Some r e s u l t s of a f i e l d study on the biology of balsam woolly aphid conducted by the Canada Dept. of Forestry In the summer of 1966 are presented i n Table t l . These data give some i n d i c a t i o n of the s i m i l a r i t y of l i f e h i s t o r y between aphids reared i n greenhouse conditions and those l i v -ing i n natural habitats. Table I I . Fecundity and duration of l i f e stages of aphids on two f i e l d p lots i n the Vancouver a r e a 1 . G.V.W.D. p l o t 1 (elev. 8001) Mt. Seymour plot (elev. 2000') No.aphids observed Value No.aphids observed Value i n s t a r I 22 7 x^eeks (mean) 3-15 weeks (range) 35 12 weeks (mean) 10-lk weeks (range) adult 5 6 weeks (minimum) k 6 weeks (minimum) fecundity -eggs/adult/week 22 3.00 h 2.89 1. Author's data, c o l l e c t e d while employed by Canada Dept. of Forestry, V i c t o r i a , B.C., and presented here by permission of Dr. L.H. McMullen. 2. Greater Vancouver Water D i s t r i c t k. E f f e c t s of F o l i a r F e r t i l i z a t i o n (a) Effects on host trees Within two days afte r i n i t i a l spraying, trees which received the 1.5$ urea treatment displayed marked needle necrosis. This e f f e c t was more severe on mineral 26 s o i l trees than on humic s o i l trees* A l i g h t degree of necrosis was observed on mineral s o i l trees which had received the 1.0$ urea treatment. Ho adverse effects were noted on trees receiving other treatments. Flushing of new growth was observed over a period of several weeks af t e r exposure of the trees to a longer photoperiod and higher temperatures. Nearly a l l trees which had received the 1.5$ urea or the 1.0$ ammonium n i t r a t e treatment exhibited new growth sooner than trees which r e -ceived other treatments. (b) E f f e c t s on aphid population The mean values of population counts, made at various times over a 10 week period following i n i t i a l t r e a t -ment, are presented i n Table I I I . Fluctuations i n the f i r s t i n s t a r population, and i n the t o t a l population (Pig.3 and 4)> were plotted along a common base l i n e (0$). Subsequent changes i n the population l e v e l s which accompanied f o l i a r treatment, have been presented as percentage changes i n the population from i n i t i a l pre-treatment l e v e l s . A comparison of trends exhibited by f i r s t i n s t a r and t o t a l aphid popula-tions f o r the control and 1$ ammonium n i t r a t e treatments has been presented i n Figure 5« 27 Table I I I . Variation i n aphid population l e v e l s (mean no. aphids/tree) over the 10 week period following i n i t i a l treatment xdth f o l i a r n u trients. Time 1 Treatment Mineral s o i l Humic s o i l Both s o i l s I 1 A 3 T 4 I A T I A T st a r t (*) 0 . 5 $ urea 1.0$ urea 1 . 5 $ urea 0 . 3 $ NH 4N0 3 1 . 0 $ NH 4N0 3 control 2 3 . 8 1 9 .8 1 8 . 6 3 9 . 0 1 5 . 0 5 . 8 5 . 8 6 .0 5 . 6 1 0 . 0 6.8 6.6 3 2 . 2 2 9 . 0 26 .0 5 1 . 6 2 k . 0 1 5 . 2 6 0 . 0 1 0 1 . 0 32 .0 5 2 . 8 5 3 . 8 1+3.8 19 . 0 35.6 1 6 4 2 0 . k l k . k 20 .k 89.O I k 5 . k 55 .6 8 5 . 2 7 3 4 7 k . 2 i l l . 8 60. k 2 5 . 3 k 5 . 9 3k 4 21).. 8 12 .k 2 0 . 8 1 1 . 0 1 5 . 2 1 0 . 6 1 3 . 5 6 0 . 6 8 7 . 2 k 0 . 8 68.1+ k 8 . 7 kk.7 3 weeks (*) 0 . 5 $ urea 1 . 0 $ urea 1.5$ urea 0 . 3 $ NHAN0 3 1 . 0 $ NH4M)5 control 2 9 4 2 5 . 8 2 0 . 0 56 .0 1 3 . 2 7.6 7.8 6.k 5 . 6 9 4 7 . 2 6 . 0 3 8 . 8 3 3 . 6 2 7 . 6 6 8 . 2 2 1 4 1 7 4 73.8 l5k.O k3 . 0 70 4 5 0 . 8 6 k . 2 1 8 . 0 3 k . 6 1 7 . 0 2 3 . 6 1 6 . 2 21.k 9 5 . 0 1 9 3 . 6 63.8 9 9 . 8 72.8 89 4 5 1 . 6 8 9 . 9 31-5 63 .2 32 .0 3 5 . 9 12.9 2 0 . 5 11 .3 1 6 . 5 11 .7 13.7 6 6 . 9 113 .6 k 5 . 7 8 k . 0 k 7 . i 5 3 4 k weeks 1 . 0 $ NH 4N0 3 control 1 2 . 0 8 . 2 5 . 8 7 . 2 19 .k 1 6 . 8 1>5.6 6 2 . 8 13 . 2 2 2 . 2 67 .k 9 0 . 6 2 8 . 8 3 5 . 5 9 . 5 l k . 7 1+34 5 3 . 7 7 weeks 00 1 . 0 $ NH4M)3 control 1 1 . 2 9 . 0 7 . 8 7.8 2 0 . 2 17.8 3 2 . 0 6 7 . 6 1 2 . k 2k.k 5 k . 0 1 0 5 . 0 2 1 . 6 3 8 . 3 1 0 . 1 1 6 . 1 3 7 . 1 6 l . k 10 weeks 0 . 5 $ urea 1 . 0 $ urea 1 . 5 $ urea 0 . 3 $ HH 4 H0 3 1 . 0 $ KH 4 N0 3 control 31.6 2 0 . 0 2 k . 0 6 0 . 6 1 3 . 0 1 2 . 0 1 7 . 0 8 . 0 l k . k 2 0 . 8 6 . 6 7 . 2 5 0 . 8 30 .6 kO.O 9 1 4 2 2 . 0 20 4 6 9 4 119.1+ 5 7 4 6 2 . 6 2 9 . 8 6 1 . 0 3 k . 6 51.8 2 1 . 2 28 .k 1 3 4 2 7 4 1 1 9 . k 1 9 0 . 6 8 k . 6 lOii .k 5 3 . 0 9 6 . 6 5 0 . 5 6 9 . 7 k 0 . 7 61.6 21.1+ 3 6 . 5 2 5 . 8 29.9 17.8 2 k . 6 1 0 . 0 17.3 8 5 . 1 1 1 0 . 6 6 2 . 3 97 .9 37.5 5 8 . 5 1. Time elapsed since i n i t i a l treatment (Sept. 1 9 t h ) . 2 . Instar I (neosistens) 3. Adult if.. Total ( a l l stages). (*-) Times at which nutrient treatments were applied. -40 I — — * - times afc which -foliar treatments applied. t - these lines not intended to represe-nt population Vends, but only as visual aid melatir\q points. Rg-3. C H A N G E S I N P O P U L A T I O N L E V E L S O F F I R S T I N S T A R A P H I D S O N H O S T T R E E S ( B O T H S O I L S ) T R E A T E D W I T H F O L I A R . N U T M E . N T 5 . C% C H A N G E F R O N V I N I T I A L P R E - T R E A T M E N T L E V E L ) . +60 _ - tiroes at which foliar nutrients applied t - these lines not intended to represent population trends, bat only as visual aid relating points, Fig.4. CHANGED IN TOTAL POPULATION LEVELS OF APHIDS ON HOST TREES (BOTH SOILS) TREATED WITH FOLIAR NUTRIENTS (% CHANGE FROM INITIAL PR.E-TREATr*ENT LEVEL). 31 5>« S t a t i s t i c a l Analysis S o i l type d i d not s i g n i f i c a n t l y a l t e r the effects of the various treatments. Thus, further analysis was ca r r i e d out to t e s t significance of the effects of treatments, excluding s o i l type as a v a r i a b l e . As can be seen i n Table IV, the mean number of aphids per tree has been adjusted (as previously described, p.17), so that population l e v e l s f o r a l l treatments are I d e n t i c a l i n i t i a l l y , both f o r f i r s t i n s t a r counts and f o r t o t a l counts. For a l l four observation dates, using a 5% l e v e l of s i g n i f i c a n c e , population l e v e l s of f i r s t i n s t a r aphids which resulted from treatment of host trees with 1% ammon-ium n i t r a t e , were d i f f e r e n t from the control populations (Table IV). Considering t o t a l aphid counts, population l e v e l s at four weeks, seven weeks, and 10 weeks, were d i f f -erent from control populations, while the difference evident after three weeks was associated with a "p" of 0.1. Changes i n population l e v e l s accompanying the other four nutrient treatments T f e r e not d i f f e r e n t from the control treatment ( p r o b a b i l i t y l e v e l of s i g n i f i c a n c e of 0.0f>). 1. Analysis using the l . s . d . and Dunnett's procedure yielded s i m i l a r r e s u l t s . 32 Table IV. Variation i n aphid population l e v e l s on host trees growing on both s o i l types over the 10 week period following i n i t i a l treatment with f o l i a r n u trients. Time 1 Treatment L i f e stage of aphids i n s t a r I 1 (neosistens) t o t a l 1 ( a l l stages) s t a r t (*) 0 , 5 $ urea 1 . 0 $ urea 1 .5$ urea 0 . 3 $ UR4HO3 1 . 0 $ NH4N03 control 38.77 3 8 . 7 7 38.77 3 8 . 7 7 38.77 3 8 . 7 7 5 8 . 4 0 5 8 . 4 0 5 8 . 4 0 5 8 . 4 0 5 8 . 4 0 5 8 . 4 0 3 weeks (*) 0 . 5 $ urea 1 . 0 $ urea 1 .5$ urea 0 . 3 $ H H 4 N O 3 1 . 0 $ NH4N03 control 4 7 . 7 5 62.kk 4®.59 5 k . 1 5 37 . 5 4 * * 53.63 64.28 7 9 . 3 3 6 6 . 6 4 72.10 5 8 . 6 4 69.70 4 weeks 1 . 0 $ NH^ NO, control 3 4 . 3 5 * * 5 3 . 2 3 5 4 . 9 4 * * 70.00 7 weeks (») 1 . 0 $ NH41TO5 control 27 .15** 5 6 . 0 3 4 8 , k 4 * * 77.70 10 weeks 0 . 5 $ urea 1 . 0 $ urea 1.5$ urea 0 . 3 $ NH4N03 1 . 0 $ HH4N03 control 4 7 . 1 5 4 5 . 8 0 55.58 5 3 . 7 2 26.22** 5 1 . 9 3 82.17 72.24 85.74 84.5S 5 0 . 4 2 * * 76.75 1. Time elapsed since i n i t i a l treatment (Sept. 1 9 t h ) . 2 . Mean no. aphids/tree (adjusted f o r covariance a n a l y s i s ) . (*) Times at which treatments were applied. ** Population decreases s i g n i f i c a n t l y d i f f e r e n t at 5$ l e v e l -33 6. Analysis of Bark Tissue Analysis of bark tiss u e from humic s o i l trees which received the control and 1% ammonium n i t r a t e treatments revealed several differences i n the nitrogen f r a c t i o n (Table V). Table V. Concentrations of ammonia and major free amino acids i n bark tissue from trees which received control and 1% ammonium n i t r a t e treatments. 1 Compound Concentration - no. j*moles/200 ^ 1. eluent control 1% NH4N03 arginine glutamic acid ornithine ammonia 2.6 x 10"3 4.0 x 10"J 54.6 x 10~5 109.8 x 10"3 69.I x 10~3 10.9 x 10"3 n i l 154.0 x 10"3 1. Analysis by J . Black, Dept. of Biochemistry, Univ. of B.C.; calculations by author. 3k DISCUSSION !• Rearing of Host Trees and Aphids (a) Host trees The techniques used i n t h i s study to c u l t i v a t e host trees on humic s o i l , and to e s t a b l i s h and sustain pop-ulations of balsam woolly aphid under greenhouse conditions were successful. However, use of a medium as d e f i c i e n t i n essential nutrients as the mineral s o i l presented complica-t i o n s . Breaking of dormancy i n mineral s o i l trees was more sporadic and resulted i n abnormal groTrth i n several trees. In those trees i n which bud fl u s h i n g was normal, growth was poor r e l a t i v e to humic s o i l trees. In addition, many mineral, s o i l trees displayed apparent resistance to aphid infestation,. I n i t i a l establishment on these trees was low ( P i g .2 ) , and on some trees, population growth was very slow. On the other hand, these problems did not mater-i a l i z e i n the humic s o i l . Breaking of dormancy was f a i r l y uniform, growth was good, and I n i t i a l establishment and growth of the aphid population was s u f f i c i e n t to f a c i l i t a t e further study. For reasons previously mentioned, A. amabilis appears to be the best choice of tree species f o r a study of t h i s nature. Balsam f i r grows well i n the greenhouse, i s r e a d i l y infested with balsam woolly aphid, and maintains populations f o r several generations. Moreover, destruction 35 of balsam f i r stands i n the P a c i f i c Northwest would repre-sent greater economic loss than f o r other true f i r s (Johnson et a l 1963). Exposure of trees to a c h i l l i n g regime of 600 hours at temperatures le s s than i|0°F. was s u f f i c i e n t to e l i c i t groi'jth response i n a l l trees. None of the 60 trees f a i l e d to break dormancy although the main stems of some trees remained dormant. A longer c h i l l i n g period of 1000 hours at the same temperatures might overcome t h i s problem of main stem dormancy}" (b) The aphid population There i s l i t t l e published information on tech-niques f o r a r t i f i c i a l l y rearing balsam woolly aphid. No one to date has been able to develop a method of rearing t h i s insect on a r t i f i c i a l nutrient media. Attempts to devise an a r t i f i c i a l substance to stimulate s t y l e t penetration have 1 met with l i t t l e success. The only available method seems to be the use of ho&t tree seedlings c u l t i v a t e d i n the green-house or growth chamber. Although the techniques employed to e s t a b l i s h and maintain populations of balsam woolly aphid under green-house conditions requires some refinement, i t was adequate to maintain populations f o r four successive generations over a period of s i x months. At termination of the study, there 1. V.J.Krajina, personal communication 2. J.Clark, personal communication 36 was no reason to believe that the existing population would not have continued to develop, given the proper environmental conditions. In comparison, DeLyzer (196£), in. h i s report of a r t i f i c i a l rearing of the woolly pine needle aphid, Schizo-lachnus piniradiatae (Viviparae) on red pine, Pinus resinosa, states that host trees would support aphid populations a maximum of only two months. Some difference of opinion exists about the l i f e 1 stage used to i n f e s t host trees. Balch maintains that bark pieces bearing large numbers of eggs should be used, whereas i Johnson suggests that large numbers of crawlers are required. Prom the r e s u l t s of t h i s study, i t i s obvious that i n f e s t i n g with eggs alone i s f u t i l e , whereas the use of bark bearing eggs and crawlers i s successful. In the four trees used to test the f e a s i b i l i t y of using eggs alone as an i n f e s t i n g stage, the f a t e of the eggs was <a mystery. Within one week, a l l eggs apparently hatched; yet there was no establishment of neosistentes on the tree s . In addition, the mid-April Infestation attempt, i n which large numbers of eggs, but few crawlers, were used, was a f a i l u r e . A possible explanation i s that emerging crawlers investigate the tree, and s e t t l e more r e a d i l y i f an aphid population already exists on the tr e e . I f not, the crawlers tend to depart from the host tree and/or di e . Supporting t h i s suggestion i s the observation that when i n f e s t a t i o n i s attempted using bark pieces bearing 1. R.E.Balch, personal communication 2 . N.E.Johnson, personal communication 37 both eggs and crawlers, the number of neosistentes which s e t t l e on the host tree i s much greater than the number of crawlers which was present on the bark. Thus the neosistens population must be composed of aphids which were crawlers at the time bark pieces were attached to the tree, and aphids which emerged from eggs subsequent to bark attachment. More-over, crawlers tend to s e t t l e i n clusters on the host. This c l u s t e r i n g may indicate that host tissue at that s i t e Is p a r t i c u l a r l y favourable as a nutrient source. Regardless of the reason, a behavioural mechanism appears to e x i s t , i n xtfhich newly hatched crawlers prefer to s e t t l e i n regions of pre-existing i n f e s t a t i o n . Certain minor modifications would improve t h i s technique of i n f e s t a t i o n and rearing. It Is desirable to concentrate the aphids on the mainstem to f a c i l i t a t e l a t e r observation. The plasticene c o l l a r s were f a i r l y successful i n l i m i t i n g migration of aphids to peripheral portions of the tree. However, they must be replaced frequently, as they dry out, and they also e l i c i t a s l i g h t swelling response i n the tree. I n i t i a l s e t t l i n g can be e f f e c t i v e l y concentrated i n one region by a l i g h t covering of absorbent cotton around the stem, under which crawlers s e t t l e . Several investigators do not use c o l l a r s , but r e l y s o l e l y on the cotton to l i m i t 1 d i s p e r s a l of the crawlers. However, once the i n i t i a l popula-t i o n of neosistentes has been established, the cotton should be permanently removed*to avoid repeated physical disturbance 1. R.E.Balch, N.E.Johnson, personal communication 38 of the wool-bearing adults during subsequent observations. Some type of g r i d mapping system seems essential f o r d e t a i l e d study of the biology of the aphid. Otherwise, observation of s p e c i f i c aphids i s d i f f i c u l t , because of t h e i r extremely small s i z e . Greenbank (1963) points out that a study of t h i s insect may be i n i t i a t e d at any time of year. Even xihen i n -fested bark pieces are c o l l e c t e d i n mid-winter, aphids resume a c t i v i t y immediately upon exposure to the warmer temperature of a laboratory or greenhouse. Another possi-b i l i t y f o r indoor study i s the use of infested pieces of 1 tree stem. McMullen reports that populations of aphids on f e l l e d trees remain a l i v e and carry on normal functions f o r three to four months a f t e r f e l l i n g . 2. Tree N u t r i t i o n and Biology of the Aphid Comprehensive reports by Balch (1952) and Varty (1956) include descriptions of the biology of A. piceae. More s p e c i f i c d e t a i l s about the l i f e h i s t o r y of t h i s insect i n the B a c i f i c Northwest are presented by Johnson and Wright (1957), M i t c h e l l et a l (1961), and Harris (1965). These „ publications are u s e f u l i n assessing the s i m i l a r i t y between the biology of n a t u r a l l y occurring populations and those reared under greenhouse conditions. 1. L.H.McMullen, personal communication 39 i(a) Exploratory behaviour of crawlers According to Balch (19^2), newly-hatched crawlers exhibit a strong upward movement towards the crown of the tree, perhaps because they a r e - p o s i t i v e l y phototactic and/or because they prefer younger feeding t i s s u e . Results of t h i s study support t h i s suggestion. However, the upward movement appears to be only an i n i t i a l response of the crawler to stimulatory f a c t o r s , such as l i g h t . Other i n f l u e n t i a l factors may be the apparent desire to s e t t l e i n a secluded, protected s i t e , preferably adjacent to previously s e t t l e d aphids, and to seek out a suitable feeding s i t e . Observations of f i e l d populations, 1 and of populations i n t h i s study, indicate considerable movement of crawlers down the stems of infe s t e d trees, away from the l i g h t source. This may explain, i n part, the c h a r a c t e r i s t i c downward spread of an i n f e s t a t i o n from the crown of the host tree (Harris 1965)* (b) S e t t l i n g rate of crawlers Even though trees growing on both s o i l regimes were i n i t i a l l y exposed to approximately the same numbers of eggs and crawlers, the rate of establishment of crawlers on humic s o i l trees was 2.5 times higher than on mineral s o i l trees (Pig.2). Such a sizeable difference i n s e t t l i n g rate i s p a r t i c u l a r l y noteworthy when one considers that a l l host 1. L.H.McMullen, personal communication ko trees were of the same provenance and were exposed to d i f f -erent s o i l regimes only s i x months p r i o r to i n i t i a l i n f e s t -ation with aphids. True aphids (Aphididae) determine s u i t a b i l i t y of the host plant only a f t e r penetrating the feeding tissue with t h e i r s t y l e t s (Auclair 1963). The difference i n s o i l f e r t i l i t y may have e l i c i t e d a change i n the chemical and/or physical c h a r a c t e r i s t i c s of celljwalls and middle lamellae i n the bark tissue (phloem and cortex), thereby making the bark of mineral s o i l trees more resist a n t to s t y l e t penetra-t i o n , or conversely, f a c i l i t a t i n g s t y l e t penetration of humic s o i l bark t i s s u e . However, In view of reports of the i n f l u -ence of s o i l f e r t i l i t y on composition of plant tiss u e (Kramer and Kozlowski i 9 6 0 , Wells 1965, Hopkins et a l I966) , i t also seems l i k e l y that some a l t e r a t i o n i n composition of the bark sap has been induced by the gross differences i n s o i l nutrient l e v e l s . Gagnon (1966) has shown that Abies  balsamea from two d i f f e r e n t s i t e s exhibits quantitative differences i n the amino acid composition of needles. Needles from trees growing on the better s i t e ( s i t e index 45) had higher concentrations of nine of the ten amino acids than needles from trees on the other s i t e ( s i t e index 32). Whether true aphids s e t t l e and feed on any given host i s determined l a r g e l y by a phagostimulatory mechanism i n the host (Beck 1965).. Phagostimulation i s now thought to be regulated p r i m a r i l y by nutrient q u a l i t y of the feeding kl t i s s u e , and more s p e c i f i c a l l y , by the balance between n i t r o -gen, sucrose, and cer t a i n amino acids i n the tissue sap ( M i t t l e r and Dadd 196£a,b). pea plants resi s t a n t to attack by the aphid, Aphis pisum, have lower l e v e l s of nitrogen and amino acids, and higher l e v e l s of sucrose, than susceptible plants (House 1961). Thus, the n u t r i e n t - d e f i c i e n t mineral s o i l may have alt e r e d the nitrogen-sucrose r a t i o and amino acid composition of the host tree sap, which i n turn, acted as a phagodeterrent by increasing the tree's resistance to ini:£ial s e t t l i n g by crawlers. (c) L i f e h i s t o r y and biology Reports on the biology of A. piceae indicate that once the neosistens has s e t t l e d at a p a r t i c u l a r feeding s i t e , i t spends the duration of i t s l i f e at that s i t e (Balch 1952, Varty 1956, M i t c h e l l et a l 1 9 6 l ) . However, within the frame-work of t h i s study, many Instances of movement of individual aphids away from o r i g i n a l feed^ing s i t e s were recorded. Most obvious was the general abandonment of host trees by the whole neosistens population which had s e t t l e d as a r e s u l t of the mid-December i n f e s t a t i o n . Movement of aphids was also observed on f i e l d p lots during the summer of 1966. Apparently, movement can occur at four times during the l i f e cycle -as a neosistens shortly a f t e r i n i t i a l s e t t l i n g , or during any of the three subsequent moults. The fate of aphids exhib-i t i n g movement Is d i f f i c u l t to determine, since i t seems 1. L.H.McMullen, personal communication 42 v i r t u a l l y impossible to follow movements of one s p e c i f i c aphid for any period of time, using conventional v i s u a l observation. Several aphids were observed attempting to r e i n s e r t t h e i r s t y l e t s at d i f f e r e n t s i t e s on the host trees, but i t i s not known whether they were successful. Balch (1952) and others state that a s e t t l e d aphid can p a r t i a l l y withdraw i t s s t y l e t s from a s p e c i f i c e x t r a c e l l u l a r space, and r e i n s e r t them into an adjacent e x t r a c e l l u l a r space, without moving from the feeding s i t e . In view of t h i s a b i l i t y , i t i s possible that aphids could Indeed abandon feeding s i t e s and r e i n s e r t t h e i r s t y l e t s at new feeding s i t e s . F a i l i n g t h i s , aphids which withdraw t h e i r s t y l e t s would undoubtedly die within a short time. M i t c h e l l et a l (196l) give an i n d i c a t i o n of the v a r i a b i l i t y i n l i f e h i s t o r y of t h i s insect i n the P a c i f i c Northwest, depending on such factors as elevation, stand density, and l a t i t u d e . Comparison of l i f e h i s t o r y data obtained from t h i s study (Table I) with f i e l d data (Table I I ) , and with that of M i t c h e l l et a l (1961), demonstrates that the aphid population reared under greenhouse conditions d i s -played a c h a r a c t e r i s t i c l i f e c y cle. L i f e h i s t o r y d i f f e r e d s l i g h t l y from that of l o c a l f i e l d populations, i n that fecund-i t y and duration of the adult stage i n the greenhouse were s l i g h t l y l e s s than i n the f i e l d . However, the greenhouse values l i e within the range of normal v a r i a t i o n i n l i f e h i s t o r y . 43 One c h a r a c t e r i s t i c which appears a t y p i c a l i s the duration of the second and t h i r d i n s t a r stages. M i t c h e l l et a l (1961) report that i n Oregon, duration of these stages i s two to three weeks each, whereas i n the greenhouse, both stages were us u a l l y completed within one week (Table I). This l a t t e r f i g u r e , however, i s i n close agreement with l o c a l f i e l d data, which shows that each of the two stages usually 1 l a s t s a maximum of one week. Other than t h i s v a r i a t i o n , the l i f e h i s t o r y of aphids reared i n greenhouse conditions was c h a r a c t e r i s t i c , when compared to documented l i f e h i s t o r i e s . Certain differences i n l i f e h i s t o r y can be r e l a t e d to the f e r t i l i t y of the s o i l supporting the host trees* (Table I ) . On humic s o i l trees, the neosistens stage was s l i g h t l y shorter, and the adult stage almost two weeks shorter, than on mineral s o i l trees. Although fecundity was s l i g h t l y higher on humic s o i l trees, reproductive p o t e n t i a l of the adult was l e s s due to i t s shorter l i f e s p a n . These variations i n duration of l i f e stages are a good i n d i c a t i o n that rate o f maturation of an insect i s determined, at l e a s t p a r t l y , by d i e t (House 1966c). An unusual feature of l i f e h i s t o r y of the green-house population was that the f i r s t generation neosistens stage was almost two weeks shorter than second and t h i r d generation neosistentes (Table I ) . This v a r i a t i o n Is not known to occur i n nature (Mitchell et a l 1961). One poss-i b l e explanation i s that the f i r s t generation neosistentes 1. L.H. McMullen, personal communication. kk arose from adults feeding on another host tree - i . e . the tree used as a source of infested bark pieces. Successive generations arose from adults feeding on the same host trees i n the greenhouse. Thus, t h i s could be acclimation of second and t h i r d generations to new host tissue and to environmental conditions of the greenhouse. Variations i n l i f e h i s t o r y i n the two f i e l d plots (Table II) may be p a r t i a l l y a ttributable to differences i n s o i l f e r t i l i t y , but the shorter neosistens stage and higher fecundity of adults on the lower plot may also be r e l a t e d to 1 higher temperatures and humidities i n that plo t -(Mitchell et a l 1961, Greenbank 1963). The effect of s o i l f e r t i l i t y om balsam woolly aphid reproduction i n t h i s region warrants further i n v e s t i g a t i o n . Johansson (I96I4.) has shown that a lowered soluble nitrogen l e v e l i n host plants i s accompanied by decreased reproduction i n true aphids. (d) Population growth Difference i n growth rate between aphid populations reared on mineral s o i l and humic s o i l trees i s considerable (Pig.2 ) . Prom August 2 0 t h to September 1 9 t h , the humic s o i l population increased by 137$, whereas the population on mineral s o i l trees increased by only 100$. This i s also evidenced by the concurrent increase of the r a t i o of mean number of aphids per humic s o i l tree to mean number of aphids per mineral s o i l tree from 2.55 to 2 . 9 0 . This difference i n 1. L.H. McMullen, personal communication 45 growth rate can be r e l a t e d to l i f e h i s t o r y data co l l e c t e d i n t h i s study (Table I ) . Although fecundity of adult aphids on both s o i l regimes i s about the same, duration of the adult stage on mineral s o i l trees i s about two weeks longer. Thus, the reproductive p o t e n t i a l of adults on mineral s o i l trees should be greater than on humic s o i l trees. In spite of t h i s , however, the population growth rate on humic s o i l trees was 37$ greater over a four week period. One possible explanation i s that crawlers s e t t l e d at a greater rate on humic s o i l trees; at the time of i n i t i a l i n f e s t a t i o n , the establishment rate of crawlers on humic s o i l trees was 2,5 times greater than on mineral s o i l trees. Presumably then, i n any one generation, a larger proportion of the population of newly-hatched crawlers on humic s o i l trees establishes i t s e l f than on mineral s o i l t rees. Factors which may i n f l u -ence s e t t l i n g of aphids on host trees, such as the physical and chemical nature of the bark surface, and the composition of host tissue sap, are discussed elsewhere (p.kO, p.55)« The l i t e r a t u r e contains several references to v a r i a t i o n i n l e v e l s of i n f e s t a t i o n among trees growing on si t e s of d i f f e r e n t q u a l i t i e s . The higher the s i t e index, the heavier the i n f e s t a t i o n of balsam woolly aphid (Balch 1952, Johnson et_ a l 1963). Varty 1 observed an unusually heavy stem attack by Adelges on pole stage balsam f i r growing next to a large manure heap. This heavy attack could be due p a r t l y 1. I.W.. Varty, personal communication U6 to a higher establishment rate of crawlers. However, clim a t i c factors may also influence rate of spread of an i n f e s t a t i o n * Smith (19^8) has shown that walking rate of the crawler increases with higher temperatures and more Intense l i g h t . An additional f a c t o r may be that fecundity of adults on trees growing on riche r s i t e s i s higher. Although the fecundities observed i n t h i s study (Table I) do not support t h i s sugges-t i o n , general f i e l d observations, made by t h i s writer and 1 other workers, indicate that aphids on r i c h s i t e f i r stands have higher fecundity than on poorer s i t e s . However, t h i s difference may be r e l a t e d to climate as well as to s o i l f e r t -i l i t y . Although Balch (19!?2) found no c o r r e l a t i o n between fecundity and host vigour or part of the tree attacked, Johansson (1964) reports that true aphids feeding on host plants with a high concentration of soluble nitrogen have greater reproductive p o t e n t i a l than on plants with low n i t -rogen l e v e l s . Moreover, true aphids feeding on host plants growing on s i t e s d e f i c i e n t i n other minerals (potassium, i r o n , magnesium, or phosphorus) are less fecund. Many other examples of the influence of s i t e f e r t i l i t y on reproduction of various phytophagous insects are reviewed by House (I96I). One major problem i n assessment of fecundity of A. piceae i s the technique used to measure egg production. Although periodic removal of a l l eggs from the adult has been used recently, and was used i n t h i s study, i t i s possible that physical disturbance of the aphid during egg removal 1. I.W. Varty, personal communication 47 depresses fecundity. Values obtained with t h i s method (Table I) are lower than mean values suggested by Balch (1952) and Varty (19£6). Perhaps the most accurate technique i s that proposed by Balch - i.e.counting the egg shel l s i n the wax wool of the dead adult. Yet t h i s method also has shortcomings, i n that some egg s h e l l s may drop o f f or be removed by agents such as wind or in s e c t s . 3. F o l i a r F e r t i l i z a t i o n and i t s Effects on the Inseet (a) E f f e c t s on population l e v e l s Certain changes i n aphid population l e v e l s were evident following treatment of host trees with f o l i a r nutr-ients (Fig.3)« On trees growing on both s o i l regimes, popu-l a t i o n l e v e l s of f i r s t i n s t a r aphids increased during the f i r s t three weeks f o r a l l treatments except 1$ ammonium n i t r a t e . The control population increased kk .8$, the popu-l a t i o n treated with 1$ ammonium n i t r a t e declined 7.0$, and populations receiving other treatments exhibited increases ranging from 23«5$ to k8.8$. A f t e r seven weeks, the control and 1$ ammonium n i t r a t e treatments had continued to exhibit t h e i r i n i t i a l trends, with the control population increasing 5k.5$ and the 1$ ammonium n i t r a t e treatment decreasing 37*3$. By the end of 10 weeks, responses to the various treatments were more diverse. Populations on trees which received 0.5$ urea and 0.3$ ammonium n i t r a t e treatments showed l i t t l e change from the three week l e v e l s , with the f i n a l increases 48 being 20.5$ and 34»2$ r e s p e c t i v e l y . The 1.0$ urea treatment ultimately resulted i n a decline i n the population from a peak of +48.8$ to a f i n a l l e v e l of +15.6$. Although t r e a t -ment with 1 .5$ urea caused severe needle necrosis i n the host trees, the aphid population continued to increase s t e a d i l y to a f i n a l l e v e l of +60.8$. Meanwhile the decline which had followed treatment with 1$ ammonium n i t r a t e l e v e l l e d o f f , and the f i n a l decrease i n the population was 37-8$. The control population also l e v e l l e d o f f and decreased s l i g h t l y to a f i n a l l e v e l of +47.0$. Although s o i l f e r t i l i t y did not s i g n i f i c a n t l y a l t e r the effects of various treatments, the adverse e f f e c t of 1$ ammonium n i t r a t e on the f i r s t i n s t a r population was more severe on humic s o i l trees (Table I E ) . On mineral s o i l trees receiving t h i s treatment, the neosistens population had de-creased 25$ at the seven week mark, but had recovered somewhat aft e r 10 weeks to a f i n a l l e v e l of -13$. A f t e r seven weeks, the humic s o i l population had declined 40.5$> and by 10 weeks, the decrease was iu4»6$. As with the neosistens populations, the t o t a l population of aphids ( a l l stages) increased with a l l t r e a t -ments except one (Pig . 4 ) « Three weeks a f t e r i n i t i a l spraying, the control population had increased 19.2$, the population which received 1$ ammonium n i t r a t e had decreased 3»3$, and the other populations had exhibited increases ranging between 10 .5$ and 30.0$. Pour weeks l a t e r , the control had continued 49 I t s increase to +37.1$, while the aphids receiving 1$ ammon-ium n i t r a t e had continued to decline to a. l e v e l of -23.8$. F i n a l l e v e l s a f t e r 10 weeks indicate that only one treatment - the 1$ ammonium n i t r a t e - had resulted i n population changes s i g n i f i c a n t l y d i f f e r e n t from the control population. In the l a s t three weeks, the control group declined s l i g h t l y to a f i n a l l e v e l of +30.9$, while those populations which received 0.5$ urea, 1.5$ urea, and 0.3$ ammonium n i t r a t e treatments continued to increase to f i n a l l e v e l s between +1+0.3$ and +52.7$. The 1.0$ urea treatment resulted i n a l e v e l l i n g off', and a f i n a l increase of 26.8$. Likewise, the 1$ ammonium n i t r a t e treatment e l i c i t e d ncjfurther change, and the f i n a l l e v e l of the population was -23.0$. As with the f i r s t i n s t a r population, the adverse ef f e c t of 1$ ammonium n i t r a t e on the t o t a l population was more pronounced on humic s o i l (Table I I I ) . A f t e r four weeks, the t o t a l population on mineral s o i l trees receiving t h i s treatment had declined 19.0$, but recovered to a l e v e l of -8.3$ a f t e r 10 weeks. On humic s o i l trees, the population decrease a f t e r four weeks was 8.5$, but t h i s decline continued to a f i n a l l e v e l of -27.8$ a f t e r 10 weeks. Trends exhibited by the control and 1$ ammonium n i t r a t e populations during the f i r s t seven weeks a f t e r i n i -t i a l treatment are more uniform than during the l a s t three weeks (Fig.3 and 1+). For the f i r s t seven weeks, the aphid population on the control trees showed a steady increase while the population on trees treated with 1$ ammonium 50 n i t r a t e declined s t e a d i l y . Thereafter, the control population declined s l i g h t l y and the 1$ ammonium n i t r a t e population l e v e l l e d o f f . Several f a c t o r s may have contributed to decline i n the control population i n the l a s t three weeks. Although the adult population continued to increase s l i g h t l y during that period (Table I I I ) , both the f i r s t i n s t a r population and the t o t a l population decreased by about 7$ (Pig.3 and I4J . This decline may be attri b u t a b l e to reduction i n o v i p o s i t i o n by adults, which was observed during November, and which i s ch a r a c t e r i s t i c of f i e l d populations i n t h i s region. Thus, the adult population continued to increase, due to maturation of younger stages, but the t o t a l population l e v e l dropped due to reduced o v i p o s i t i o n and decreased replacement of the neo-sistens population. Another possible explanation f o r t h i s decline i s that the aphid population l e v e l may have approached the carrying capacity of the humic s o i l host trees. Throughout the l a s t three weeks, the control population on mineral s o i l trees increased from the +17$ to the +34$ l e v e l , while the humic s o i l control population declined from the+41*7$ to the +30.1$ l e v e l . Concomitant with these changes, the mean aphid population per mineral s o i l tree at the 10 week mark was only about 20, whereas the mean population per humic s o i l tree was almost 100 (Table I I I ) . I t would be d i f f i c u l t to explain population changes exhibited by f e r t i -l i z e d tre®s i n terras of carrying capacity, since t h i s char-a c t e r i s t i c may be alt e r e d by n u t r i t i o n a l status of the host. 51 During the l a s t seven weeks, the f i r s t i n s t a r population declined i n the 1,0$ urea treatment group (Pig.3) . This delayed effect of urea on the aphids could be due to the fa c t that i t may not be metabolized as quickly as ammon-ium n i t r a t e (Wittwer and Teubner 1959)- Urea, as such, i s seldom absorbed by trees d i r e c t l y , and i t i s thought that the action of urease i n metabolizing urea to ammonia i s r e l -a t i v e l y weak, and may l i m i t the rate of reaction. Thus l i b -eration of ammonia from urea breakdown would be gradual and more prolonged than from breakdown of ammonium n i t r a t e . Although t h i s delayed suppression of the population i s obser-vable with 0.5$ urea and 1.0$ urea treatments, the populati©n receiving the 1.5$ urea treatment continued to increase throughout the observation period ( F i g . 3 ) . Why t h i s higher concentration of urea exerted a reverse ef f e c t on the aphids i s not evident. It may be that the severe needle necrosis r e s u l t i n g from treatment disturbed the tree's physiology to such an extent that the urea had l i t t l e or no ef f e c t on composition of the phloem sap, either because i t was not e f f e c t i v e l y absorbed, or because urease a c t i v i t y was inhib-i t e d . In the 1$ ammonium n i t r a t e treatment group, popu-l a t i o n l e v e l s of f i r s t i n s t a r aphids, and of a l l stages, remained unchanged during the l a s t three weeks (Pig.3 and . As well, the adult population remained f a i r l y constant (Table I I I ) . This indicates that the establishment rate of crawlers 52 was greater than during the f i r s t seven weeks, and that t h i s increased s e t t l i n g resulted i n equilibrium between replace-ment of the population by s e t t l i n g crawlers, and depletion of the population, due pri m a r i l y to adult m o r t a l i t y . Such: \ an increase i n s e t t l i n g may be re l a t e d to two f a c t o r s . Dur-ing the l a s t part of the observation period, a l l host trees treated with Vfo ammonium n i t r a t e exhibited a f l u s h of new growth, not observed i n most of the other trees. The concom-ita n t increase i n protein synthesis would necessitate more rapid metabolism of ammonium n i t r a t e and ass i m i l a t i o n of breakdown products f o r amino acid synthesis. Such rapid incorporation of nitrogen into new tissue would preclude maintenance of elevated nitrogen i n the sap, trtiich may have rendered the feeding t i s s u e unsuitable to the insect during the f i r s t seven weeks. The second p o s s i b i l i t y i s that the residual aphid population which survived the i n i t i a l f o l i a r treatment became acclimated to the altered nutrient balance i n the host t i s s u e . I f so, t h i s would indicate that within the l i f e s p a n of one generation, aphids had acquired a wider tolerance to dietary nitrogen l e v e l s , and had passed t h i s increased tolerance on to t h e i r progeny, since the crawlers exhibited greater tendency to s e t t l e i n the l a s t three weeks than during the f i r s t seven xreeks. 53 (b) L i f e stages affected The decrease r e s u l t i n g from treatment with 1% ammonium n i t r a t e can be attr i b u t e d to large reductions i n the f i r s t i n s t a r aphid population (Pig.5). In the control population, the growth curve of the t o t a l population i s a r e f l e c t i o n of changes i n the population of f i r s t i n s t a r aphids. Likewise, the growth curve showing the decrease i n t o t a l population, when treated with 1% ammonium n i t r a t e , r e f l e c t s the decrease seen i n the f i r s t i n s t a r population of the same treatment group. Examination of changes i n popu-l a t i o n l e v e l s of various l i f e stages (Table III) supports th i s suggestion that the f i r s t i n s t a r stage demonstrates a much greater negative response to t h i s treatment than the adult stage. Merker (196l) describes the adverse effect of nitrogen f e r t i l i z e r s on adelgids, as an increase i n l a r v a l mortality, and undoubtedly, the crawler ( l a r v a l ) population i n t h i s study has been affected i n the same way. However, to be more s p e c i f i c , reduction observed i n the neosistens population appears to be due primarily to a decreased craw-l e r s e t t l i n g rate, and not to increased mortality amongst previously s e t t l e d aphids. One can i n f e r that those crawlers which do not s e t t l e u l t i m a t e l y die. Thus, the increased mortality rate of crawlers i s caused by i n h i b i t i o n of se t t -l i n g , which i n turn, has been Induced by f e r t i l i z a t i o n of the host trees with Vfo ammonium n i t r a t e . 54 The suggestion that t h i s treatment i n h i b i t s s e t t -l i n g i s supported by the e a r l i e r observation that s e t t l i n g rate was greatly influenced by the f e r t i l i t y of the s o i l on which host trees were growing (Pig.2), i n d i c a t i n g that craw-l e r s may be sensitive to nutrient composition of the host t i s s u e . Thus, any f a c t o r which induces an a l t e r a t i o n i n the composition of feeding t i s s u e , such as s o i l f e r t i l i t y or f o l i a r f e r t i l i z a t i o n , may a f f e c t the s e t t l i n g rate of craw-l e r s . A secondary f a c t o r contributing to the decline i n the f i r s t i n s t a r population, i s that some neosistentes may have abandoned the host trees after composition of the feeding t i s s u e was alt e r e d by f e r t i l i z a t i o n . M i t t l e r and Dadd (196£b) observed a s i m i l a r response i n true aphids, when the amino acid concentration i n phloem sap of the host plant was de-creased. A f t e r the mid-December i n f e s t a t i o n was ostensibly successful i n t h i s study, the neosistentes abandoned the host trees gradually over a two month period. Moreover, i n the l i f e h i s t o r y study, many neosistentes were observed to de-part from t h e i r o r i g i n a l feeding s i t e s shortly a f t e r i n i t i a l s e t t l i n g , or while moulting into the second i n s t a r stage. (c) Mode of action of nitrogen f e r t i l i z e r s I f the suggestion i s true that f e r t i l i z a t i o n of the host trees with 1% ammonium n i t r a t e reduced the aphid population by i n h i b i t i n g s e t t l i n g of crawlers, and perhaps by stimulating s e t t l e d neosistentes to abandon host trees, i t i s possible that some form of host resistance has been 55 induced. At l e a s t three mechanisms of resistance seem poss-i b l e . A decrease i n the aphid population might be r e l a t e d to change i n physical c h a r a c t e r i s t i c s of the bark such that s t y l e t penetration i s i n h i b i t e d . For example, the population density of spruce sawfly, P r i s t i p h o r a abietina, decreased a f t e r s o i l f e r t i l i z a t i o n with lime (Ohnesorge 1957). This reduction may be r e l a t e d to increased l i g n i f i c a t i o n of host plant t i s s u e , which i s known to follow addition of lime (Anonymous 1964). Decrease In the aphid population may also be r e l a t e d to chemical change i n the bark - e.g. odour -which i n h i b i t s probing by the aphid, or i t may r e s u l t from a change i n nutrient composition of the feeding t i s s u e -i . e . the phloem and cortex (Schwenke I 9 6 2 ) . As w i l l be ex-plained l a t e r , t h i s l a t t e r suggestion i s strongly implicated i n most of the current theories of host resistance. In e a r l i e r studies of the mechanisms of host plant resistance, the orthodox view was that food s e l e c t i o n by phytophagous insects i s e s s e n t i a l l y recognition In the host plant of certain:"non-nutritious token stimulants, quite unrelated to n u t r i t i o n a l value of the host ( M i t t l e r and Dadd 196k), More recently however, t h i s hypothesis has been re-jected or modified. Current theories of host resistance have been reviewed by Beck (19&5)» and most investigators now suggest that resistance i s influenced by feeding 1. In older trees, balsam woolly aphid feeds on sap i n e x t r a c e l l u l a r spaces of the c o r t i c a l parenchyma (Balch 1952), but the bark of trees i n t h i s study i s so t h i n that insects may have fed d i r e c t l y from phloem t i s s u e . 56 stimulants and deterrents, which are re l a t e d to nutrient composition of the host. Sugars, amino acids, s t e r o l s , phospholipids, ascorbic acid, and some B-vitamins have a l l been implicated as phagostimulants and phagodeterrents. The importance of nutrients was elucidated Tirtien Kennedy and Booth ( 1 9 5 D proposed that host selection was based on the insect's response to certain"flavour s t i m u l i " , such as glycosides and a l k a l o i d s , and to "nutrient s t i m u l i " i n the plant. Experimental evidence to date strongly supports the theory that nutrients are involved i n the phagostimulatory mechanism of many phytophagous insects (Dadd and M i t t i e r 1 9 6 5 a ,b). L i t t l e published information exists on host s e l -ection by A. piceae. However, adelgids and true aphids, being members of the same superfamily Aphidoidea (Imms 1961}.), have many s i m i l a r i t i e s i n biology and l i f e h i s t o r y . Conse-quently, i t i s worthwhile to consider the body of knowledge on aphid feeding behaviour, i n any attempt to explain changes i n establishment rate of balsam woolly aphid, r e s u l t i n g from host tree f e r t i l i z a t i o n . Recent work by M i t t l e r and Dadd ( 1 9 6 4 , 1965a ,b) on true aphids (Aphididae) has l e d them to propose a theory of phagostimulation, i n which the significance of sugars and amino acids i s stressed. These two nutrients, which repre-sent the major components of natural food of aphids, have powerful e f f e c t s on feeding behaviour. Phagostimulation depends p r i m a r i l y on sugar l e v e l s , and secondarily on the $1 amino acid composition of host t i s s u e . Although sucrose alone stimulates feeding, a mixture of sucrose and a cert a i n com-binati o n of amino acids has an even stronger phagostimulatory e f f e c t on the aphid, Myzus persicae, i n d i c a t i n g that the amino acid f r a c t i o n may function as a synergist to stimulate feeding when combined with sugar. However, a solution of amino acids alone has no phagostimulatory e f f e c t . M i t t l e r and Dadd conclude that "the q u a l i t a t i v e and quantitative differences i n amino acids and sugars known to exist between re s i s t a n t and susceptible plants, and between d i f f e r e n t developmental stages i n one and the same plant, not only influence aphids i n a n u t r i t i o n a l manner, but may also have a more Immediate eff e c t which i s expressed i n the r e l a t i v e acceptance of d i f f e r e n t species, v a r i e t i e s , or developmental stages of plants." This theory can be r e l a t e d to more general sugges-tions about the mechanism whereby f e r t i l i z e r s adversely af f e c t some f o r e s t i n s e c t s . The most common theory i s the "sugar hypothesis", stated f i r s t by Schwenke (1962), and thereafter by Francke-Grossman (1963) and Johansson (196k). It i s proposed that nitrogen f e r t i l i z a t i o n manifests i t s adverse effect on insects by increasing the nitrogen l e v e l i n leaves, thereby reducing the concentration of sugars. Such an a l t e r a t i o n changes the water balance of the tree, and i n so doing, upsets the rel a t i o n s h i p which supposedly exists between s o i l , f e r t i l i z a t i o n , water balance of plants, and insect outbreaks (Schwenke I960). Sugar concentration 58 of the host t i s s u e i s of prime importance. Any factor which lowers #he sugar concentration w i l l thereby exert an adverse eff e c t on the insect population. Thus, nitrogen f e r t i l i z a t i o n , which induces a decrease i n sugar concentration, i s followed by reduction i n the insect population. Conversely, drought increases sugar concentration, with the r e s u l t that insect reproduction i s increased (Merker 1962). S p e c i f i c e f f e c t s of f e r t i l i z e r s on i n d i v i d u a l phytophagous insects have been described by Merker (1961, 1962). With f e r t i l i z a t i o n , mineral l e v e l s of the host plant are elevated, and these minerals accumulate i n s p e c i f i c tissues of the insect - e.g. the Malpighian tubules — s e r i -ously disturbing i t s metabolism. Merker proposes that such a disturbance renders the insect more susceptible to adverse clim a t i c conditions. Thus, depending on severity of metabolic disturbance, the e f f e c t of f e r t i l i z e r s could be considered i n h i b i t o r y or t o x i c . Although knowledge of nitrogen metabolism In trees i s l i m i t e d , studies indicate that organic nitrogen, i n the form of amino acids, amides, and ureides, constitutes almost a l l of the nitrogen f r a c t i o n i n tree xylem sap (Bollard 1958, Kramer and Kozlowski i 9 6 0 ) . Moreover, the, most abundant n i t -rogen compounds i n xylem sap of conifers are aspartic acid, asparagine, glutamic acid, and glutamine. In h i s studies of the composition of phloem sap of the willow, S a l i x a c u t i f o l i a , 59 i n which sap was c o l l e c t e d from the severed s t y l e t s of the willoxtf aphid, Tuberolachnus salignus, M i t t i e r (1953, 1958) i d e n t i f i e d many of the same amino acids as had been i d e n t i -f i e d i n xylem sap. The major portion of t o t a l nitrogen i n -gested by aphids i s i n the form of amino acids and amides, es p e c i a l l y glutamine, asparagine, arginine, glutamic acid, and aspartic acid (Auclair 1963). Apparently, the aphid does not hydrolyze protein; therefore, the amino acid-amide complement of the ingesta i s representative of phloem sap. Much knowledge has accumulated with regard to the effects of f e r t i l i z e r s on nutrient composition of plants. Although nitrogen f e r t i l i z a t i o n of common food crops such as r i c e , corn, wheat, and barley, r e s u l t s i n an elevated protein content, q u a l i t y of t h i s protein may be reduced due to an amino acid imbalance induced by f e r t i l i z a t i o n (Harris and von Loesecke i960). Nitrogen f e r t i l i z a t i o n of com produces an imbalance such that the proportion of l y s i n e i s reduced, and the food product i s , i n e f f e c t , l y s i n e - d e f i c i e n t . In a study of the effects of f e r t i l i z a t i o n of barley with ammonium n i t r a t e , McBeath et a l (i960) found that t o t a l protein con-tent was elevated, but the balance of amino acids, which included glutamic acid, arginine, and l y s i n e , was seriously upset. Moreover, Carter and Larsen (1965) have shown that l e v e l s of t o t a l nitrogen, amino nitrogen, and amide nitrogen i n xylem sap of l o b l o l l y pine are Increased by f e r t i l i z a t i o a a with nitrogen compounds. 60 The importance of food q u a l i t y to insects has been emphasized by several investigators. F e r t i l i z a t i o n of host plants a l t e r s the chemical composition of tissue and thereby changes the n u t r i t i v e value of the plant f o r insect pests (Rodriguez I 9 6 0 ) , Moreover, House ( 1 9 6 5 , 1966a) has found that nutrient balance i n host tissue i s much more important i n regulating insect feeding and n u t r i t i o n than concentrations of various nutrients. The importance of arginine, aspartic acid, and glutamic acid, i n regulating growth and development i n true aphids and other insects has been described by Maltais ( 1 9 5 9 ) , Patton ( 1 9 6 3 ) , and Gilmour ( 1 9 6 5 ) . I t seems that f e r t i l i z a t i o n with 1% ammonium n i t r a t e exerts i t s adverse e f f e c t on the balsam woolly aphid by a l t e r -ing nutrient composition of the host t i s s u e , which i n turn, suppresses phagostimulation. Since true aphids determine s u i t -a b i l i t y of a host plant e s s e n t i a l l y by probing and penetrating the tissue (Auclair 1 9 6 3 , M i t t l e r and Dadd 1 9 6 5 a ) , the process of host s e l e c t i o n involves t e s t i n g the composition of host tissue to determine i t s a c c e p t a b i l i t y . As was previously mentioned, nutrient composition of the feeding t i s s u e , par-t i c u l a r l y nutrient balance, i s a major factor influencing phagostimulation. The importance of the nitrogen-sugar r a t i o and amino acid f r a c t i o n of the food source was also described. I t i s clear that f e r t i l i z a t i o n with 1% ammonium n i t r a t e resulted i n gross changes i n the amino acid comp-o s i t i o n of host tree bark tiss u e (Table V). The arginine 61 concentration of f e r t i l i z e d tissue was about 25> times greater than the untreated control, while the high ornithine l e v e l i n the control tissue disappeared completely a f t e r f e r t i l i -zation. In addition, smaller increases i n the concentrations of glutamic acid and ammonia followed f e r t i l i z a t i o n . Although a t o t a l nitrogen analysis of bark tissu e was not carr i e d out, i t i s l i k e l y that t o t a l nitrogen was increased by f e r t i l i z a -t i o n with ammonium n i t r a t e (Schwenke 1962, Carter and Larsen 1965), thereby a l t e r i n g the nitrogen-sugar r a t i o . In l i g h t of these data and current theories on mechanisms of host resistance, i t would seem that, i n t h i s study, f e r t i l i z a t i o n with 1$ ammonium n i t r a t e exerted i t s adverse e f f e c t on the balsam woolly aphid p r i m a r i l y by increasing resistance of the host tree to i n i t i a l s e t t l i n g by crawlers. This p a r t i c u l a r f e r t i l i z e r has induced consider-able change i n the amino acid complement and the resultant imbalance may have rendered feeding tissue of the host unsuit-able to many crawlers. Neosistentes already feeding p r i o r to f e r t i l i z a t i o n may have withdrawn t h e i r s t y l e t s and abandoned the host tree a f t e r the composition of feeding tissue was alter e d by f e r t i l i z a t i o n . Rather than a toxic e f f e c t , t h i s appears to be an i n h i b i t i o n of host s e l e c t i o n or phagostimu-l a t i o n , r e s u l t i n g from ammonium nitrate-induced alt e r a t i o n s i n the nutrient composition of host t i s s u e . Further study might reveal that s e t t l e d , feeding aphids are also affected by changes i n food quality* Such 62 a l t e r a t i o n s may r e s u l t i n malnutrition, and c e r t a i n "deficiency diseases", such as decreased growth and repro-duction, and increased m o r t a l i t y of younger stages, may develop (House 1 9 6 3 ) . It should be emphasized that, since uptake of sap by true aphids i s regulated only by turgor pressure and i s therefore indiscriminate (Kennedy and M i t t l e r 1953), these insects are vulnerable to changes i n food q u a l i t y of sap, which might be induced by f e r t i l i z a t i o n . h* Amino Acid Composition of Host Tissue C h a r a c t e r i s t i c a l l y , glutamine, glutamic acid, aspara-gine, and aspartic acid represent the predominant amino acids and amides found i n conifers and other trees (Kramer and Kozlowski i 9 6 0 , Carter and Larsen 1 9 6 5 )• However, Gagnon (1966) found that the most abundant amino acids i n needles of balsam f i r , A. balsamea, and black spruce, Picea mariana, were tyrosine, alanine, and p r o l i n e . Analysis of bark tissue (phloem and cortex) from the control population of A. amabills used i n t h i s study revealed that ornithine was most abundant (Table V). Only low l e v e l s of arginine and glutamic acid were detected. However, t h i s analysis was carried out on tissue c o l l e c t e d from only f i v e humic s o i l trees, and because of t h i s , these data are of l i m i t e d significance at present. I n t e r - s p e c i f i c differences, both q u a l i t a t i v e and quantitative, may occur i n the amino acid f r a c t i o n of needle tissue of conifers (Gagnon 1 9 6 6 ) . Moreover, quantitative differences 63 i n the amino acid composition of needles may occur within a single species growing on d i f f e r e n t s i t e s . Besides i t s adverse effect on the aphid population, a secondary benefit of 1% ammonium n i t r a t e i s that i t stimu-l a t e d new growth i n host trees more r a p i d l y and more consis-t e n t l y than did any other treatment. Thus, such a treatment exerts a two-fold e f f e c t , by simultaneously decreasing the balsam woolly aphid population and promoting formation of new growth i n the host t r e e . 5» Future Investigation One major purpose of t h i s study was to investigate the general r e l a t i o n s h i p between host tree n u t r i t i o n and the balsam woolly aphid, to determine which aspects warranted more intensive study. In t h i s respect, the in v e s t i g a t i o n was successful. A r i s i n g out of the r e s u l t s of thi s study are several questions which could be investigated i n the future. For example, i t would be desirable to experiment more with dosage response, to determine which concentration of ammonium n i t r a t e would produce the greatest adverse e f f e c t on the Insect population. Duration of t h i s adverse e f f e c t , and long range response of the insect population, aft e r one appl i c a t i o n of ammonium n i t r a t e should also be ascertained. To gain deeper understanding of the mechanism whereby phagoinhibition i s induced by f e r t i l i z a t i o n , more extensive analyses should be done to determine the effects of f e r t i -l i z e r s on the physical and chemical properties of bark t i s s u e . 6k Reports indicate that many phytophagous insects exhibit changes i n l i f e h i s t o r y - e.g. reproduction - when host tissue composition i s altered . I t would be desirable to determine whether ammonium n i t r a t e does i n fac t a l t e r l i f e h i s t o r y of the balsam woolly aphid population remaining on the tree a f t e r f e r t i l i z a t i o n . A longer range i n v e s t i g a t i o n might be designed to det-ermine whether the balsam woolly aphid adapts to selection pressure of repeated f e r t i l i z e r treatments, with the r e s u l t that a population i s produced which thrives under the modi-f i e d nutrient regime. A c e r t a i n sequence of various nutrients, applied at s p e c i f i c time i n t e r v a l s , might make adaptation of the insect to any one nutrient supply impossible, and the adverse effect could thereby be sustained over a long period. The effects of other nitrogen compounds containing mineral ions such as potassium, calcium, sulphur, etc., could also be investigated to determine t h e i r influence on the insect population and host tree. Furthermore, i t would be desirable to know whether the ammonia ion or n i t r a t e ion Is more i n f l u e n t i a l i n mediating the adverse effect of ammonium n i t r a t e . I f further i n v e s t i g a t i o n strengthens the hypothesis that populations of balsam woolly aphid may be regulated by f e r t i l i z e r - i n d u c e d changes i n the host t i s s u e , more general research might then be undertaken. For example, one could study the effects of such f e r t i l i z e r s on populations 65 of other phytophagous insects, such as de f o l i a t o r s and l e a f miners. In addition, i t would be desirable to ascertain whether the same nutrient compounds, when absorbed through the root system, e l i c i t s i m i l a r response i n the insect population. 66 SUMMARY AND CONCLUSIONS Balsam f i r seedlings were cultured i n the greenhouse on two s o i l regimes - a nutMent-deficient mineral s o i l , and a f e r t i l e humic s o i l . A l l trees were infested with balsam woolly aphid crawlers (larvae). The rate of crawler establishment and population growth, and the biology of the insect, were then studied. Infested trees were l a t e r treated with f o l i a r nutrients, using various concentrations of urea and ammonium n i t r a t e , and the ef f e c t of treatment: on aphid population growth was studied. Bark tissu e of host trees receiving the control and 1% ammonium n i t r a t e treatments was analysed f o r free amino acids and ammonia. Conclusions of thi s study are as follows: 1. A technique was developed f o r greenhouse rearing of populations of balsam woolly aphid on Abies amabilis seedlings. 2 . The rate of crawler establishment and population growth of aphids was greater on humic s o i l host trees than am mineral s o i l host trees. 3. The f i r s t i n s t a r and adult stages were shorter on humic s o i l trees than on mineral s o i l t r e e s . k. F o l i a r a p p l i c a t i o n of Vfo ammonium n i t r a t e resulted i n s i g n i f i c a n t decrease i n the aphid population on treated trees over a 10 week period. Other nutrients tested did not 67 s i g n i f i c a n t l y influence population growth rate. $, F o l i a r a p p l i c a t i o n of 1$ ammonium n i t r a t e e l i c i t e d quantitative and q u a l i t a t i v e changes i n the amino acid f r a c t i o n of bark t i s s u e . This treatment also promoted forma-t i o n of new growth on host trees. Composition of host feeding t i s s u e , as influenced by s o i l f e r t i l i t y and chemical f e r t i l i z e r s , may modify the i n t e r a c t i o n between the host, A. amabilis, and i t s insect pest, A. piceae. The host i s r e l a t i v e l y non-selective i n i t s absorption and translocation of nutrients and likewise, the aphid i s indiscriminate i n i t s uptake of sap from the host. Such a phenomenon offers opportunity to develop resistance i n the host, by rendering feeding tissue unsuitable to the i n s e c t , through the addition of nutrients. 68 LITERATURE CITED 1 . Anonymous 1964. Notes on progress i n forest science. For. Abstr. 2 5 ( l ) : x i i i 2 . A u c l a i r J.L. 1 9 6 3. Aphid feeding and n u t r i t i o n . Ann. Rev. Ent. 8 : 4 3 9 - 4 9 0 3 . Balch R.E. 1 9 5 2 . Studies of the balsam woolly aphid, Adelges piceae (Ratz.) and i t s effects on balsam f i r , Abies balsamea (L.) M i l l . Can. Dept. A g r i c . Publ. « 6 7 , 76 pp. 4« , J . Clark, and J.M. Bonga 1964* Hormonal action i n production of tumours and compression wood i n Abies balsamea by Adelges piceae. Nature 2 0 2 ( 4 9 3 3 ) : 721-722 5 . Beaton J.D., I. MacRae, and R.C. Speer 1965* F o l i a r analysis of Douglas f i r from a e r i a l forest f e r t i l i -zation t r i a l s on Vancouver Island, B.C. Paper presented at Fourth C a l i f o r n i a Forest S o i l F e r t i l i t y Conference. 6 . Beck S.D. 1965» Resistance of plants to i n s e c t s . Ann. Rev. Ent. 10:207-232 7 . Bollard E.G. 1958 Nitrogenous compounds In tree xylem sap, pp. 8 3 - 9 4 . In K.V. Thimann (ed.),' Physiology of f o r e s t t r e e s . Ronald Press Co., New York 8 . Boynton D. 1954* N u t r i t i o n by f o l i a r a p p l i c a t i o n . Ann. Rev. Plant Physiol. 5 : 3 1 - 5 4 9 . Carter M.C. and H.S. Larsen 1965* S o i l nutrients and lob-l o l l y pine xylem sap composition. For. S c i . 1 1 ( 2 ) : 2 l 6 - 2 2 0 1 0 . DeLyzer A.J. 1 9 6 5 . Rearing of the woolly pine needle aphid Schizolachnus piniradiata.e, Viviparae. J . Econ. Ent. 5b1 (5) : 1021-1022 1 1 . Dadd R.H. and T.E. M i t t l e r 1 9 6 5 a . Studies on the a r t i f i c i a l feeding of the aphid Myzus persicae -I I I . Some major n u t r i t i o n a l requirements. J. Insect Physiol. 1 1 : 7 1 7 - 7 4 3 1 2 . 1 9 6 5 b . N u t r i t i o n a l requirements of the aphid Myzus persicae i n r e l a t i o n to the s u i t a b i l i t y of host plants. Proc. XII Int. Congr. Ent., London 69 1 3 . Francke-Grossman H. 1 9 6 3 . Some new aspects i n forest entomology. Ann. Rem. Ent. 8 :l|.l5-ii38 ll].. Gagnon J.D. 1 9 6 6 . Free amino acid content i n needles of Abies balsamea and Picea mariana growing on d i f f e r e n t s i t e s . Nature 212(506!*) :81& li{.. Gallagher L.U. 1964 Study on the ef f e c t s of f e r t i l i z a t i o n with nitrogen and phosphorus on growth and n u t r i t i o n of Abies amabilis with associated greenhouse t r i a l s . Unpublished M.F. th e s i s , College of Forestry, Univ. of Washington, Seattle 15• Gilmour D. 1965 The metabolism of ins e c t s . Oliver and Boyd, London 1 6 . Greenbank D.O. I 9 6 3 Limitations imposed by climate on the d i s t r i b u t i o n and abundance of the balsam woolly aphid. Interim Res. Rep, of Can. Dept. For., For. Ent. and Path. Branch, Fredericton (unpubl.). l ? . Hagner S. et a l 1966 Virkesframstallning genom skogsgSd-s l i n g (Timber production by fo r e s t f e r t i l i -zation) . Sartryck ur Sveriges SkogsvardsfBrbunds  T i d s k r i f t , Hflfte 2 1 8 . Harris J.W.E. 1965 The balsam woolly aphid, Adelges piceae (Ratz.) i n B r i t i s h Columbia. Rep, of For. Res. Lab., For. Insect and Disease Survey, Can. Dept. For., V i c t o r i a . 1 9 . Harris R.S. and H. vonLoesecke i 9 6 0 N u t r i t i o n a l evaluation of food processing. John Wiley and Sons. 2 0 . Hopkins H.T., E.H. Stevenson, and P.L. Harris I 9 6 6 S o i l factors and food composition. Amer. J . C l i n . Nutr. 1 8 : 3 9 0 - 3 9 5 2 1 . House H..L. 1961 Insect n u t r i t i o n . Ann. Rev. Ent. 6:13-26 2 2 . 1963 N u t r i t i o n a l diseases.,pp. 133 -160. In E.A. Steinhaus (ed.) Insect pathology, Vol . I. Academic Press, New York 70 23« House H.L. 1965 Effects of low l e v e l s of nutrient;, con-tent of a food and of nutrient imbalance on the feeding and n u t r i t i o n of a phyto-phagous l a r v a , Celerio euphorbiae. Can. Ent. 9 7 : 6 2 - 6 8 2 k . 1966a The r o l e of n u t r i t i o n a l p r i n c i p l e s i n b i o l o g i c a l c o n t r o l . Can. Ent. 9 8 : 1 1 2 1 - 1 1 3 4 2 5 • 1966b E f f e c t s of varying the r a t i o between amino acids and other nutrients i n conjunc-t i o n with a s a l t mixture on the f l y , Agria a f f i n i s . J . Insect Physiol. 1 2 : 2 9 9 - 3 1 0 2 6 . 1966c E f f e c t s of temperature on the n u t r i t i o n a l requirements of an Insect, Pseudosarcophaga  a f f i n i s , and i t s probable ecological s i g -n i f i c a n c e . Ann. Ent. Soc. Amer. 1 2 : 4 0 9 - 4 1 7 27* Imms A.D. 1964 A general textbook of entomology,(9th ed.) Methuen and Co. Ltd., London 2 8 . Johansson A.S. 1964 Feeding and n u t r i t i o n i n reproductive processes i n i n s e c t s . In Insect reproductiom, Symp. Ho. 2 , Roy. Ent. S o c , London, pp . 4 3 - 5 5 2 9 . Johnson H.E. and K.H. Wright 1957 The balsam woolly aphid problem i n Oregon and Washington. P a c i f i c H.W. For, and Range Exp. Station, U.S.D.A. For. Serv. Res. Pap. No. l b , 3k" pp. 3 0 . Johnson H.E., R.G. M i t c h e l l , and K.H. Wright 1963 Mortality and damage to P a c i f i c s i l v e r f i r by the balsam woolly aphid i n S.W. Washington. J . For. 6 1 : 8 5 4 - 8 6 0 3 1 . Kennedy J.S. and CO. Booth 1951 Host alte r n a t i o n i n Aphis fabae (Scop.). I. Feeding preferences and fecundity i n r e l a t i o n to the age and kind of leaves. Ann. Appl. B i o l . 3 8 : 2 5 - 6 4 32. Kennedy J.S. and T.E. M i t t l e r 1953 A method f o r obtaining phloem sap v i a the mouth parts of aphids. Nature 1 7 1 : 5 2 8 33» Krajina V.J. 1 9 6 5 Biogeoclimatic zones and biogeocoenoses of B r i t i s h Columbia., pp. 1 -17 . In V.J. Krajina (ed.) Ecology of western Horth Amer-i c a , Dept. of Botany, Univ. of B.C. 71 34» Kramer P.J. and T.T. Kozlowski i 9 6 0 Physiology of trees. McGraw-Hill Book Co., New York 35* Maltais J.B. 1959 Feeding the pea aphid Acyrthosiphon pisum (Harr.) on plant cuttings i n organic nutrient solutions. Can. Ent. 91:336-340 36. McBeath D.K. et a l i 9 6 0 The n u t r i t i o n a l value of increased l e v e l s of protein r e s u l t i n g from nitrogen f e r t i l i z a t i o n of barley. Can. J . Animal S c i . 4 0 : 5 7 - 5 8 37* Merker E. i 9 6 0 Der Ei n f l u s s des Baumzustandes. auf die Uber-vermehrung einiger Waldschadlinge. Z. Angew. Ent. 4 6 : 4 3 2 - 4 4 4 . 38« 1961 Welche TJrsachen hat die Schldigung der Insekten durch Dungung ira Walde? Allgem. Forst-u. Jagdztg. 132:73-82 39. 1962 Augenblicklicher Stand der Untersuchungen fiber die schadigende Wirkungsweise von Dtlngestoff en. auf Waldschldlinge. Allgem. Forst-u. Jagdztg. 133:81-83 4 0 . M i l l e r F.J.L. and K.V.R. Szarmes ? F o l i a r f e r t i l i -z ation i n f o r e s t r y . Res. and Develop. Div.,Cominco, T r a i l , B.C. 4 1 . M i t c h e l l R.G., N.E. Johnson, and J.A. Rudinsky 1961 Seasonal h i s t o r y of the balsam woolly aphid i n the P a c i f i c Northwest. Can. Ent. 93:794-798 4 2 . M i t t l e r T.E. 1953 Amino acids i n phloem sap and t h e i r excretion by aphids. Nature 172:207 4 3 . 1958 Sieve-tube sap v i a aphid s t y l e t s , pp. 4 0 1 - 4 0 5 . In K.V. Thimann (ed.) Physiology of forest trees. Ronald Press Co., New York 4 4 * and R.H. Dadd 1964 Gustatory, discrimination between l i q u i d s by the aphid Myzus persicae. Ent. exp. and appl. 7:315-328 4 5 • 1965a Differences i n probing responses of Myzus persicae e l i c i t e d by di f f e r e n t feeding solutions behind a Parafilm membrane. Ent. exp. and appl. 8:107-122 72 46. M i t t l e r T . E . a n d R . H . Dadd 1965b F e e d i n g b e h a v i o u r o f t h e a p h i d Myzus p e r s i c a e i n r e l a t i o n t o t h e s u i t a b i l i t y o f h o s t p l a n t s . P r o c . X I I I n t . C o n g r . E n t . , L o n d o n 47» M o r g a n M . F . 1941 C h e m i c a l s o i l d i a g n o s i s b y t h e u n i v e r s a l s o i l t e s t i n g s y s t e m . B u l l . 450, C o n n e c t i c u t A g r i c . E x p . S t a t . New H a v e n , C o n n . 48. M u s t a n o j a K . J . a n d A . L . L e a f 1965 F o r e s t f e r t i l i z a t i o n r e s e a r c h , 1957-1964. B o t a n i c a l R e v . 31(2) :l51-2lj.6 49* O e c h s s l e r G. 1962 S u c k i n g i n j u r i e s t o t i s s u e s o f n a t i v e and e x o t i c f i r s c a u s e d b y C e n t r a l E u r o p e a n f i r a p h i d s . Z . Angew . E n t . 50:408-454 50. O h n e s o r g e B . 1957 U n t e r s u c h u n g e n u b e r d i e P o p u l a t i o n s -d y n a m i k d e r K l e i n e n F i c h t e n b l a t t w e s p e . Z . Angew . E n t . 40:443-493 51. P a t t o n R . L . 1963 I n t r o d u c t o r y . i n s e c t p h y s i o l o g y . W . B . S a u n d e r s C o . , P h i l a d e l p h i a 52. R o d r i g u e z J . G . i960 N u t r i t i o n o f t h e h o s t a n d r e a c t i o n t o p e s t s . P u b l . Am. A s s . A d v m t . S c i . 61:149-167 53« S chwenke W. i960 U b e r d i e W i r k u n g d e r W a l d d u n g u n g a u f d i e M a s s e n v e r m e h r u n g d e r K i e f e r n b u s c h h o m b l a t t -wespe ( D i p r i o n p i n i L . ) 1959 i n M i t t e l -f r a n k e h u n d d i e h i e r a u s a b l e i t b a r e n g r a d o -l o g i s c h e n F o l g e r u n g e n . Z . Angew. E n t . 46:371-378 54. 1962 Neue E r k e n n t n i s s e u b e r E n t s t e h u n g a n d B e g e g n u n g v o n M a s s e n v e r m e h r u n g e n a n K i e f e r n u n d F i c h t e n n a d e l n f r e s s e n d e r S c h a d i n s e k t e n . Z . Angew . E n t . 50:137-142 55« S h i b a m o t o T . a n d H . Nakazawa 1 9 6 0 a S t u d i e s on f o l i a g e u r e a s p r a y i n g . F o l i a r a b s o r p t i o n o f u r e a b y s e e d l i n g s o f S u g i ( C r y p t o m e r i c a j a p o n i c a D . D o n . ) . J . J a p . F o r . S o c . 42(11):392-394 56. S h i b a m o t o T . et a l 1960b S t u d i e s o n f o l i a g e u r e a s p r a y i n g (l7» F o l i a r u r e a a b s o r p t i o n arid g r o w t h o f S u g i ( C r y p t o m e r i c a j a p o n i c a D. D o n . ) s e e d l i n g s . J . J a p . F o r . S o c . 42(10):352-355 73 57. Smith B.C. 1958 Responses to l i g h t and the influence ©f l i g h t and temperature on locomotion of crawlers of Adelges piceae and of insect predators of t h i s species. Can. Ent. 90(4):193-201 58. stark R.W. 1965 Recent trends i n forest entomology. Ann. Rev. Ent. 10:303-324 59. Steel R.G.D. and J.H. Tor r i e i960 P r i n c i p l e s and proced-ures of s t a t i s t i c s . McGraw-Hill Book Co., New York 60. Varty I.W. 1956 Adelges insects of s i l v e r f i r s . Forestry Commission B u l l . 26, 75 PP«> H.M. Stationery O f f i c e , Edinburgh 61. Wittwer S.H. and H.B. Tukey 1957 F o l i a r feeding. Sunset Magazine, April :55-56 62. and F.G. Teubner 1959 F o l i a r absorption of mineral n u t r i e n t s . Ann. Rev. Plant Physiol. 10:13-32 63. Wells C.G. 1965 Nutrient relationships between s o i l s and needles of l o b l o l l y pine (Pinus taeda). Proc. S o i l S c i . Soc. Amer. 29(5):621-624 

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