The Searching Behaviour of the Predatory Midge Larva
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THE SEARCHING BEHAVIOUR OF THE PREDATORY MIDGE LARVA, Feltiella acacatisuga VALLOT (DIPTERA: CECIDOMYIIDAE), IN RESPONSE TO THE DENSlTY AND DISTRIBUTION OF ITS PREY, T&anychus u&ue KOCH (ACARI: TETRANYCHIDAE) Marc Johnston B .Sc. McGill University, 1993 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PEST MANAGEMENT in the Department of Biological Sciences Q Marc Johnston SIMON FRASER UNIVERSITY July 1997 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. National Library Biblioth&que nationale of Canada du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellmgton Street 395, rue Wellington OnawaON KlAON4 Onawa ON K 1 A OW Canada Canada 4 bur !@ Norre retefence c. 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APPROVAL Name: Marc Albert Peter Johnston Degree: Master of Pest Management Title of Thesis: The searchmg behaviour of the predatory midge larva, Feltiella acurisuga Vallot (Diptera: Cecidomyiidae) in response to the density and distribution of its prey Terranvchus urticae Koch ( Acari: Tetranychdae). Examining Committee: Chair: Dr. J.Price, Assistant Professor ~r.B. Roitberg, Professor, Senior Supervisor Department of Biological Sciences, SFU ackauer, Professor Depart ent of Biological Sciences, SFU - Dr. D. Gillespie, Researcn scientist Agriculture Canada Dr. S. ~itzpatrick,Rese Agriculture Canada Public Examiner. - / P FC Date Approved: ~~lj3 '' I ABSTRACT Searching efficiency is one of the criteria used to evaluate natural enemies for biological control potential in greenhouses. The searching behaviour of a predatory gall midge larva (Feltiella acarisuga) was examined at high and low prey (Tetranychus urticae) density (10 and 5 T. urticae eggs I cm2) on the underside of tomato leaflets. Larvae significantly increased number of feeds, residence time and turning rate and decreased speed in response to higher prey density. Immediately after a feeding episode, "local search" behaviour, characterized by a signiftcant reduction in speed and a significant increase in turning rate, was triggered. Speed and turning rate then gradually increased and decreased respectively, returning to "ranging" levels after about 15 min if more prey were not encountered and consumed. Larvae usually followed a forward-moving noisy loop after consuming a prey item. The ability to alter search behaviour in response to prey density becomes more advantageous as prey become more aggregated in distribution. A survey of T. urticae density and distribution within greenhouse tomato plants in a commercial greenhouse found that at the within-leaflet level, T. urticae eggs were very aggregated (s2/m = 2.53) while adults and juveniles were moderately aggregated (s21m = 1.22). Egg aggregation was found to increase with egg density at the within-leaflet level. The survey also found that adults and juveniles were most dense in the highest stratum of plants (1.39 1cm2) and less dense in the middle and lowest strata (1.27 1 cm2 and 1.11 1 cm2 respectively). Eggs were most densely distributed in the middle stratum (7.24 1 cm2), less dense in the upper stratum (4.89 / cm2) and least dense (1.1 1 I cm2) in the lower stratum of the tomato pht. The combined results of the search behaviour experiment and the T. urticae survey suggest that F. acarisuga larvae employ a search strategy that is highly efficient. It allows them to increase consumption rate and increases their chances of being able to pupate on a single leaflet, thus avoiding the glandular hairs on the stems and leaf petioles of tomato plants. The results also suggest that the predator will show a strong aggregative response to their prey. The results of this study are being used to estimate some of the biological parameters that are needed to construct a simulation model of F. a-suga - T. wticue population dynamics. ACKNOWLEDGEMENTS I would like to thank Dr. B. Roitberg for his guidance, support and optimism. I am gratefid to Dr. D. Gillespie for his valuable suggestions and for always making his resources available. Thanks also go to Dr. M. Mackauer for his statistical advice and skillful editing. I am also gratefbl to Amos Bouskila, Mike Robinson, Ed van Randen, and Ed Mondor for their assistance and encouragement. I would like to thank my Wy (Aida, Lawrence and Valerie) and Tiara for their patience and understanding. Financial assistance was provided by the Western Greenhouse Growers Cooperative Association, a graduate fellowship fiom Simon Fraser University and a NSERC grant to Dr. B. Roitberg. TABLE OF CONTENTS APPROVAL ................................................................................... ABSTRACT .................................................................................... ACKNOWLEDGEMENTS................................................................... TABLE OF CONTENTS ..................................................................... LIST OF TABLES ............................................................................ LIST OF FIGURES ........................................................................... L INTRODUCTION ........................................................................ A The problem ................................................................................. B . Life history of Feltiella acmar?suga........................................................ C . Selecting, evaluating and improving the efficiency of natural enemies.................. IL SEARCH BEHAMOUR OF Feltiella acarisuga LARVAE AT TWO PREY DENSITIES .................................................................................. A Introduction ................................................................................ B . Methods .................................................................................... (i) Rearing four-day-old Feltiella a-suga larvae ........................ fii) Feltiella a-suga search behaviour at two prey densities ............ (i) Videotaping specifications.................................................. (iv) Interpretation of search paths fiom the videotapes....................... C . Results ...................................................................................... (i) Differences in search paths at high and low prey density ............... (ii) Changes in search behaviour induced by individual feeding episodes (at high prey density) ........................................................... 14 (iii) Specific locomotory patterns associated with larval local search ..... 15 D . Discussion .................................................................................. 16 IIL SURVEY OF TSSM DENSITY AND DISTRIBUTION WITHIN TOMATO PLANTS ......................................................................................... A. Introduction.................................................................................. B . Methods ...................................................................................... C . Results ........................................................................................ D . Discussion .................................................................................... IV .CONCLUSIONS ......................................................................... REFERENCES ................................................................................ APPENDIX I ......................................................................................................... vii LIST OF TABLES Table 1 a. Summary of search behaviour of F. acarisuga results at high and low prey (T. urticae eggs) density. Ten trials at both prey densities were performed. Leaf area, rearing group and taping time were kept consistent for trials at both prey densities. Residence time and number of feeds at the two prey densities are shown.............................................. 36 Table 1 b. Summary of search behaviour of F. acarisuga results at high and low prey (T. urticae eggs) density. Ten trials at both prey densities were performed. Travel time, distance traveled, number of turns, speed and turning rate at both prey densities are shown.......................................................................................................................... 38 Table 2. Speeds and turning rates of F. acarisuga 2 rnin before and 2 min after a feeding episode (on T. urticae eggs). Only 6 episodes could be used to make valid independent comparisons................................................................................................................ 40 Table 3 a. Densities, variances and variance to mean ratios (aggregation indices) of T. urticae eggs