Effect of Three Food Plants of Lipaphis erysimi Kalt. (Hemiptera: Aphididae) on the Area of Discovery and Killing Capacity of Its Parasitoid, Diaeretilla rapae (Mcintosh) (Hymenoptera: Braconidae)

Abstract

ABSTRACT The searching efficiency of Diaeretiella rapae was shown by the area of discovery (Nicholson & Bailey, 1935) which decreases non-linearly with increasing parasitoid density in the case of all the three tested food plants of the aphid Lipaphis erysimi. This decrease was least in aphids bred on Brassica oleraceo followed by those bred on Brassica campestris and Raphanus sativus. However, when the host density increased, both the area of discovery and k-value increased up to 50 hosts but thereafter decreased in case of aphids bred on all three tested food plants. The area of discovery and k-value were both highest with B. oleracea bred aphids followed by B. campestris and R. sativus bred aphids. Leaf texture of food plants and the interference between the parasitoids at higher densities are suggested as causes for this type of behavioural response, which is explained by the population model of Hassell & Varley (1969). For the mass rearing of the parasitoid, B. oleracea is an ideal food plant. If B. oleracea is not available, the next choice should be B. campestris.