Efficacy of pesticides on the functional response on larval ectoparasitoid, Habrobracon hebetor Say (Hymenoptera: Braconidae)

Abstract

Exposing to sub-lethal and low lethal doses of pesticides may cause changes in natural enemy behavioural, such as functional, response. In this study, the effects of chlorpyrifos, carbaryl, abamectin and spinosad were evaluated on the functional response of the Habrobracon hebetor to different densities of last instar larvae of Anagasta kuehniella Zeller. Young adult females of the parasitoid were exposed to LC30 of chlorpyrifos, carbaryl, abamectin and spinosad that were 0.32, 4.03, 3.05 and 17.51 mg a.i./l for 24 h, respectively. Host densities of 2, 4, 8, 16, 32 and 64 were offered to treated young females for 2 h in 10-cm Petri dishes and then the parasitism data were recorded. Experiments were conducted in eight replications. Functional response type was determined using logistic regression and the parameters were appraised by non-linear regression using statistical analysis software. Functional response was type Ш in control and insecticide treatments. Searching efficiency in control, chlorpyrifos-, carbaryl-, abamectin- and spinosad-treated wasps were 0.008 ± 0.002, 0.002 ± 0.0009, 0.0034 ± 0.0013, 0.0076 ± 0.002 and 0.0073 ± 0.002 h−1and handling times were 1.38 ± 0.1, 7.64 ± 1.01, 3.3 ± 0.315, 1.55 ± 0.1 and 1.46 ± 0.11 h, respectively. Chlorpyrifos and carbaryl had the highest effect on searching efficiency of H. hebetor. Spinosad and abamectin showed less adverse effect on the functional response parameters. Finally, after conducting the advanced field studies, spinosad and abamectin may be used as a compatible chemical material with biological control agent in integrated pest management programmes.