Effects of Insecticides on Oviposition and Host Discrimination Behavior in Trichogramma chilonis (Hymenoptera: Trichogrammatidae)

Trichogramma chilonis Ishii is an important natural enemy of many lepidopterous pests on various crops. Effects of two conventional insecticides on oviposition and host discrimination behavior in T. chilonis were evaluated in the laboratory through video tracking. During the oviposition period, when the number of host eggs was limited (only one host egg), females exposed to beta-cypermethrin LC1 or LC20 exhibited significantly higher feeding and re-drilling rate and significantly longer post-oviposition duration than control females. Spinosad LC20 treatment not only decreased the wasp oviposition rate but also significantly extended the oviposition duration. When the number of host eggs was six, similarly, females exposed to spinosad LC20 exhibited a significantly lower oviposition rate (79.2%) than control ones (100%). In the host discrimination experiment, females exposed to LC20 of both tested insecticides (beta-cypermethrin and spinosad) spent significantly more time on the extra-patch area. The females that survived spinosad LC20 could not discriminate between unparasitized and parasitized host eggs. Our study suggests that even the LC1 and LC20 of the tested insecticides had negative effects on the oviposition and host discrimination behavior of T. chilonis. Thus, the use of these two insecticides should be carefully evaluated.