Abstract
This paper reports on a comparative study on the response of two related parasitoids to kairomone of their hosts. Leptopilina heterotoma (Thomson) attacks larvae of Drosophila in fermenting fruits and Leptopilina fimbriata (Kieffer) attacks larvae of mainly Scaptomyza pallida (Zetterstedt) in decaying plants. In both species the response to water-soluble kairomone involves a reduction in walking speed and an increase in the frequency with which the substrate is probed. However, essential differences in some of the behavioural parameters between the two species were also discovered. Upon en- countering a substrate with kairomone L. heterotoma starts to walk more with longer strolls, whereas L. fimbriata is arrested more strongly and starts to walk less with shorter strolls. The differences in response are possibly adaptations to differences in natural host distribution and density as found in the two microhabitats.