Learning and Its Effect on Host-Finding by Exeristes Roborator (F.)
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LEARNING AND ITS EFFECT ON HOST-FINDING BY EXERISTES ROBORATOR (F.) (HYMENOPTERA : ICHNEUMONIDAE) Aileen R. Wardle B.Sc. (Hons.), University of British Columbia, 1976 M.P.M., Simon Fraser University, 1984 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Biological Sciences @ ~ileenR . Wardle 19 88 SIMON FRASER UNIVERSITY NOVEMBER 1988 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author i i APPROVAL Name: Aileen Ruth Wardle Degree : Doctor of Philosophy Title of Thesis: LEARNING AND ITS EFFECT ON HOST-FINDING BY EXERISTES ROBORATOR (F.) (HYMEN0PTERA:IcHNEmoNIDAE) Examining Comnittee: Chairman : --- -- .H. Borden, Professor, Senior Supervisor Dr. ~k%ckauer, Professor Dr. B.D. Roitberg, Associate Professor \,b . - .. - - . Arthur, Research Scientist, Agr. Cda., on, Sas$atchewan, Public Examiner l/YP -- , Research Scientist, Agr. Cda. , , Public Examiner 1 Dr. E .A. Gays,Professor, ~i~-bfBiol. Control & Entomol. Sci., U. of California, Berkeley, California, External Examiner . PARTIAL COPYRIGHT LICENSE I horoby grant to Slmon' Frasor Unlvors I ty tho r lght to i ond my thasis,,proJoct or oxtondod ossay'(th0 ?Itlo of whlch Is shown bolow) to users of tho Slwh Frosor ~nlvorslt~~lbr&~, ond to ma,ko partial or single coplcs only for such usors or In rosponso to a roquost from tho 1 i brary of my othor un lvors l ty, or othor oducat lona l Inst l tut Ion, on its own bohalf or for ono of Its usors. I furthor agroo that permission for multlplo copying of thls work for scholarly purposos may bo grantod by mo or tho Doan of Graduato Studios. It Is undorstood that.copylng or publlcatlon of thls work for flnanclal- galn, shal 1 not bo allowod without my wrltton pormlsslon. '% . C.. TI t lo of Thos 1 s/ProJoct/Extondod Essay Learning and its effect on host-finding by Exeristes roborator (F. ) (~~meno~tera:Ichneumonidae ) . Author: - (slgnaturo) Aileen Ruth Wardle ( namo iii ABSTRACT In laboratory experiments females of the polyphagous, ichneumonid parasitoid Exeristes roborator (F.) were able to learn the colour, form, and odour of artificial host microhabitats in which they attacked hosts. The amount and timing of experience that females gained attacking hosts influenced the strength of their learned responses. Individuals learned from one host attack, but their learning was strengthened considerably by a second such attack, and increased somewhat more after further experience. Attacks on hosts carried out within the first 2 days after this activity began appeared to be most effective at causing learning. Females denied experience until more than 2 days had passed after first host attack still learned, but did not exhibit as strong learned responses as females gaining experience when younger. Parasitoids that attacked hosts first in one artificial microhabitat and then in a second learned to shift their responses to the second microh'abitat, but did not transfer them completely. Apparently oviposition is not necessary reinforcement for learning, as attacks involving only host probing and feeding caused learning to occur. In laboratory and field cage* experiments, parasitoids given experience with hosts in an artificial microhabitat subsequently exhibited significantly lower responses to a natural host/microhabitat system than inexperienced females. When females were given prior experience with the natural system, their responses to it were not increased over those of inexperienced insects, but they appeared to respond almost exclusively to this familiar system, while inexperienced females responded readily to other insect-infested vegetation present in the test arena. It is possible that the experimental conditions did not allow increased, learned responses to the natural system to be detected. Alternatively, learning may enhance the parasitoid's responses only to some natural host microhabitats, or may not significantly increase its responses to natural microhabitats. However, these results suggest that experience with either a natural or an artificial host/microhabitat system prior to release may interfere with a biological control agent's post-release response to a different target system. I would like to thank Messrs. A. Syed and M. Horta for advice and assistance with insect rearing, Ms. M. Siekkinen for technical advice, Mr. W. Brown, Ms. M. Mather, and Ms. D. Schroeder for production of a steady supply of experimental insects, Ms. L. Wheeler and Ms. C. Matteau for help with experimental work and insect rearing, Dr. S. Allan for instruction in the use of a spectrophotometer and discussion of insect vision, and Dr. G. Judd for advice on experimental design and statistical analysis. I would also like to thank Drs. R.D. Routledge and M.A. Stevens and Ms. S. Ng for statistical advice, Mr. R.G. Long for photography, and Mrs. E. Carefoot for artwork. Special thanks are due to Drs. M. Mackauer and B.D. Roitberg for helpful discussions and critical review of this manuscript. I would especially like to thank Hugh Brock for his extreme patience an; understanding, and my supervisor Dr. J.H. Borden for his support, encouragement, and advice over the course of this work. This research was funded by the National Sciences and Engineering Research Council of Canada, Operating Grant no. A3881 to J.H. Borden, an NSERC Postgraduate Scholarship, and an H.R. MacMillan Family Fund Fellowship. TABLE OF CONTENTS Page Approval ................................................................ ii ABSTRACT ............................................................... iii ACKNOWLEDGEMENTS ........................................................ v List of Tables .......................................................... ix List of Figures ......................................................... xii GENERAL INTRODUCTION ................................................... 1 CHAPTER 1 . LEARNING OF HOST MICROHABITAT COLOUR ........................ 6 Introduction .......................................................... 7 Materials and Methods ................................................. 9 Insect rearing and maintenance .................................... 9 Learning of host microhabitat colour .............................. 9 Effect of experience with hosts in microhabitats of different reflectance intensities ........................................... 18 Statistical ~nalysis .............................................. 19 Results ............................................................... 22 6 Discussion ............................................................ 36 CHAPTER 2 . LEARNING OF HOST MICROHABITAT FORM .......................... 39 Introduction ........................................................ 40 Materials and Methods ................................................. 42 Results ............................................................... 49 Discussion ............................................................ 56 CHAPTER 3 . LEARNING OF HOST MICROHABITAT ODOUR ......................... 59 Introduction ...................................................... 60 Materials and Methods ................................................. 62 Learning of host microhabitat odour ............................... 62 Effect of odour learning on response to egg cups in a cage bioassay .......................................................... 69 Statistical analysis .............................................. 69 vii Results ............................................................... 71 Discussion .......................................................... 76 CHAPTER 4 . HOW AND WHEN EXERISTES ROBORATOR LEARNS ..................... 79 Introduction ...................................................... 80 Materials and Methods ................................................. 85 A . Behaviour of E . roborator towards egg cups containing hosts ......................................................... 85 B . Tests for learning from exposure to hosts in egg cups prior to host attack .......................................... 85 C . Importance of experience with hosts after commencement of host attack .................................................. 88 D . Time at which experience most influences behaviour ............ 94 E . Learning a second host microhabitat ........................... 99 Statistical analysis .............................................. 102 Results ............................................................. 104 Discussion ......................................................... 121 CHAPTER 5 . EFFECT OF PRIOR EXPERIENCE ON THE RESPONSE OF EXERISTES ROBORATOR TO A NATURAL HOST AND MICROHABITAT ................ 127 Introduction .......................................................... 128 Materials and Methods ................................................. 132 Parasitoids. hosts. and host microhabitats ........................ 132 Preliminary test of the effect of prior experience with hosts in natural and artificial microhabitats on the response of E . roborator to Scots pines infested with R . buoliana ............. 133 Effect of prior experience with hosts in natural and artificial microhabitats on the short-term response of E . roborator to Scots pines infested with R . buoliana in a field cage ....................................................... 136 Effect of prior experience with hosts in natural and artificial microhabitats on the long-term (23 h)