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POPULATION DYNAMICS OF THE CABBAGE APHID, BREVICORYNE BRASSICAE (HOMOPTERA: APHIDIDAE) AT VANCOUVER, BRITISH COLUMBIA: IV. PREDATION BY APHIDOLETES APHIDIMYZA (DIPTERA: CECIDOMYIIDAE)

Published online by Cambridge University Press:  31 May 2012

D. A. Raworth
Affiliation:
Research Station, Agriculture Canada, Vancouver, British Columbia V6T 1X2

Abstract

Predation of the cabbage aphid, Brevicoryne brassicae (L.), by the cecidomyiid Aphidoletes aphidimyza (Rond.) was studied in the laboratory and the field. Predation was random with respect to aphid instar, and predation rate was constant with respect to aphid density. A. aphidimyza consumed 1.7 times more aphids in the laboratory than in the field during larval development. When aphid weight and age distribution were accounted for, it was found that the same biomass, 2.14 mg, was eaten in both cases.

The pupal developmental temperature threshold for A. aphidimyza was 9.2 °C. The developmental times of the egg, larval and pupal stages, and complete life cycle were 32°, 66°, 171°, and 283°D9.2. In the field, there was at least 5 times more food available on individual leaves than was necessary for larval development, suggesting that female A. aphidimyza took care to place their eggs where there was sufficient food for larval development.

The numerical response of A. aphidimyza to aphid density was calculated using sample data from three field plots. The response between plots was not statistically different.

The implications of using prey weight rather than number to measure predator consumption, and biological control of aphids by A. aphidimyza, are discussed.

Résumé

La prédation du puceron du chou, Brevicoryne brassicae (L.), par le cécidomyidé Aphidoletes aphidimyza (Rond.) a été étudiée en laboratoire et sur le terrain. Les captures se faisaient au hasard, indépendamment du stade larvaire, et le taux de prédation demeurait constant, indépendamment de la densité des pucerons. A. aphidimyza consommait 1.7 fois plus de pucerons en laboratoire que sur le terrain durant le développement larvaire. En tenant compte du poids des pucerons et de la répartition des âges, nous avons constaté que la même biomasse, soit 2.14 mg, était consommée dans les deux cas.

La température qui déclenchait le développement des pupes d'A. aphidimyza était de 9.2 °C. Le temps de développement de l'oeuf, de la larve et de la pupe ainsi que le cycle biologique complet étaient de 32, 66, 171 et 283°J9,2. Sur le terrain, il y avait au moins cinq fois plus de nourriture disponible sur les feuilles prises individuellement que ce qui était nécessaire au développement larvaire, ce qui laisse entendre que la femelle d'A. aphidimyza prenait soin de déposer ses oeufs là où il en avait suffisamment pour assurer la croissance des larves.

Les implications de l'utilisation du poids des proies plutôt que de leur nombre pour mesurer la consommation des prédateurs ainsi que le recours à la lutte biologique contre les pucerons livrée par A. aphidimyza sont discutées.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1984

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