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THE EFFECT OF HOST DENSITY ON EGG DISTRIBUTION BY THE SOLITARY PARASITOID APHIDIUS NIGRIPES (HYMENOPTERA: APHIDIIDAE)1

Published online by Cambridge University Press:  31 May 2012

Conrad Cloutier
Conrad Cloutier
Affiliation:
Département de Biologie, Université Laval, Ste-Foy, Québec G1K 7P4
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Abstract

Egg distribution by the solitary parasitoid Aphidius nigripes was studied experimentally at 14 densities of the host aphid, Macrosiphum euphorbiae. The number of hosts parasitized increased with host density, the functional response being of Holling's type II. However the average number of eggs/female was not significantly affected by host density, and consequently superparasitism increased with decreasing host density. When egg distributions were tested against random models, higher than predicted numbers of both unparasitized and superparasitized hosts were observed at all densities tested. Further analysis assuming random search suggested that female A. nigripes tend to deposit several eggs per host while experiencing a low rate of encounter with hosts. The ecological significance of this behaviour is examined.

Résumé

La distribution des oeufs a été étudiée expérimentalement chez le parasitoide Aphidius nigripes à 14 densités de son hôte aphidien, Macrosiphum euphorbiae. Le nombre d'hôtes parasités a augmenté avec la densité d'hôtes, la réponse fonctionnelle étant du type II de Holling. Cependant, le nombre d'oeufs/femelle n'a pas été affecté significativement par la densité d'hôtes et en conséquence, le superparastisme a augmenté avec la diminution de la densité d'hôtes. Une comparaison des distributions de fréquence du nombre d'oeufs/hôte avec des modèles aléatoires a révélé que les nombres d'hôtes non parasités et superparasités étaient plus élevés que prédit à toutes les densités testées. L'analyse poursuivie en présumant que le parasitoide avait un comportement de recherche aléatoire a révélé une tendance claire de la femelle A. nigripes à déposer plusieurs oeufs par hôte lorsqu'elle rencontre des hôtes avec une fréquence réduite. La signification écologique de ce comportement est abordée dans la discussion.

Type
Articles
Information
The Canadian Entomologist , Volume 116 , Issue 6 , June 1984 , pp. 805 - 811
Copyright
Copyright © Entomological Society of Canada 1984

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