Sublethal effects of dimethoate, imidacloprid, and thiodicarb on the biological parameters of Aenasius bambawalei (Hymenoptera: Encyrtidae)

The endoparasitic wasp, Aenasius bambawalei Hayat (Hym.: Encyrtidae), is one of the most effective parasitoids of cotton mealybug, Phenacoccus solenopsis Tinsley (Hem.: Pseudococcidae), in Iran. Since natural enemies alone are not able to keep the population of mealybug under economic injury level, the use of chemical insecticides is inevitable. In this study, the effects of sublethal concentrations of 0.5, 1 and 25 ppm of dimethoate, thiodicarb and imidacloprid were investigated on the life table parameters and survival of the parasitoid in laboratory conditions. The results showed that the fertility of the female parasitoids decreased in insecticidal treatments and the length of the total preoviposition period (TPOP) increased. However, the length of the adult preoviposition period (APOP) and the longevity of females did not change. Moreover, the intrinsic rate of increase (rm), the finite rate of increase (λ), and the net reproduction rate (R0) in dimethoate and thiodicarb treatments were significantly lower than control, but in imidacloprid treatment, the difference was not significant. According to these results, imidacloprid had less negative effects than the other two inecticides on the growth parameters and the life table of A. bambawalei.