Comparative study of the population level effects of carbaryl and abamectin on larval ectoparasitoid Habrobracon hebetor Say (Hymenoptera: Braconidae)

Habrobracon hebetor Say is one of the most important ectoparasitoids of the larval stage of many invasive agricultural pests such as noctuid and pyralid moths. Lethal and sublethal effects of carbaryl and abamectin were assessed on the ectoparasitoid H. hebetor in laboratory conditions. Dose–response bioassays were carried out on immature and adult stages by using dipping and contact residue methods, respectively. LC₅₀ (lethal concentration for 50%) values of carbaryl and abamectin were 31.19 and 4.16 mg a.i. l⁻¹ on larval stage and 12.6 and 4.42 mg a.i. l⁻¹ on adults, respectively. In order to assess the sublethal effects, adult wasps were exposed to an LC₃₀ of each insecticide and then the demographic parameters of live wasps were studied. The results showed that the intrinsic rate of increase (r _m ), finite rate of increase (λ), net reproductive rate (R₀) and gross reproductive rate (GRR) were significantly affected by the insecticides. The highest and the lowest r _m values were 0.23 and 0.17 in control and carbaryl-treated insects, respectively. The sex ratio of H. hebetor offspring was not significantly affected by either insecticide. The results showed that carbaryl had more adverse effects on population parameters of the parasitoid compared to abamectin. Field studies are needed to determine the total effects of the pesticides on H. hebetor.