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)

The searching efficiency of Diaeretiella rapae was shown by the area of dis covery (Nicholson & Bailey, 1935) which decreases non-linearly with increas ing parasitoid density in the case of all the three tested food plants of t he aphid Lipaphis erysimi. This decrease was least in aphids bred on Brassi ca oleracea followed by those bred on Brassica campestris and Raphanus sati vus. However, when the host density increased, both the area of discovery a nd k-value increased up to 50 hosts but thereafter decreased in case of aph ids 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 a nd R. sativus bred aphids. Leaf texture of food plants and the interference between the parasitoids at higher densities are suggested as causes for th is type of behavioural response, which is explained by the population model of Hassell & Varley (1969). For the mass rearing of the parasitoid, B. ole racea is an ideal food plant. If B. oleracea is not available, the next cho ice should be B. campestris.