Lethal and Demographic Impact of Chlorpyrifos and Spinosad on the Ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae).

Abstract

The appropriate use of biological agents and chemical compounds is necessary to establish successful integrated pest management (IPM) programs. Thus, the off-target effects of pesticides on biological control agents are essential considerations of IPM. In this study, the effects of lethal and sublethal concentrations of chlorpyrifos and spinosad on the demographic parameters of Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were assessed. Bioassays were carried out on immature and adult stages by using dipping and contact exposure of dry pesticide residue on an inert material, respectively. The lethal concentration (LC)50 values of chlorpyrifos and spinosad were 3.69 and 151.37 ppm, respectively, on the larval stage and 1.75 and 117.37 ppm, respectively, on adults. Hazard quotient (HQ) values for chlorpyrifos and spinosad were 400 and 2.2, respectively, on the larval stage and 857.14 and 2.84, respectively, on adults. A low lethal concentration (LC30) was used to assess the sublethal effects of both pesticides on the surviving females. In each treatment, 25 survivors were randomly selected and transferred into 6-cm Petri dishes. Adults were provided daily with last instars of Anagasta kuehniella (Zeller) as a host until all of the females died. The number of eggs laid, percent of larvae hatched, longevity, and sex ratio were recorded. Stable population growth parameters were estimated by the Jackknife method. In control, chlorpyrifos, and spinosad treatments, the intrinsic rates of increase (r m) values were 0.23, 0.10, and 0.21, respectively. The results of this study suggest a relative compatibility between spinosad use and H. hebetor. Finally, further studies should be conducted under natural conditions to verify the compatibility of spinosad with H. hebetor in IPM programs.