Effects of traditional insecticides on Habrobracon hebetor (Hymenoptera: Braconidae): bioassay and life-table assays

Abstract

The lethal and sublethal effects of the insecticides chlorpyriphos and fenpropathrine, which are overused in tomato production, were evaluated on the larval, pupal and adult stages of the parasitoid Habrobracon hebetor in the laboratory. Dose-response bioassays were carried out on immature and adult stages by using dipping and contact residue methods, respectively. The LC50 of chlorpyriphos varied from 40 to 2000 times less than the recommended field rate and 10–100 times less for fenpropathrine treatments on the different life-history stages. To assess the sublethal effects, all life-history stages were exposed to LC25 equivalent concentration of each insecticide and the demographic parameters of surviving parasitoids were studied. In LC25 tests on adult stage, mean longevity and fecundity showed significant differences between chlorpyriphos (15.93 ± 1.37 d and 128.20 ± 20.20 eggs) and fenpropathrine (12.76 ± 0.78 d and 124.00 ± 12.27 eggs) as compared with the control (20.41 ± 0.72 d and 281.00 ± 12.95 eggs). In addition, net reproductive rate and intrinsic rate of increase indicated significant differences between chlorpyriphos (22.89 ± 6.43 and 0.19 ± 0.02) and fenpropathrine (14.44 ± 3.58 and 0.17 ± 0.02) as compared with the control (55.55 ± 12.54 and 0.24 ± 0.02). Briefly, we can conclude that both insecticides had negative effects on H. hebetor. However, the negative effect of fenpropathrine on rm was higher than that of chlorpyriphos. In conclusion, field studies are recommended to determine the total effects of these insecticides on H. hebetor.