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

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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.