Effects of the mixed biocide Bacillus thuringiensis-abamectin on the development of the parasitoid Microplitis mediator and its host Helicoverpa armigera

Abstract

The effects of the mixed biocide Bacillus thuringiensis Berliner with abamectin (BtA) on the development of the parasitoid Microplitis mediator (Haliday) (Hymenoptera: Braconidae) and its cotton bollworm host, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), were evaluated in the laboratory. Weight gain in larvae of H. armigera was initially delayed, but larval developmental period increased and pupal weight increased when they were fed on a diet containing BtA. Due to increased longevity of the host larvae, the susceptible period to parasitization of H. armigera by M. mediator increased when the host larvae were reared on diets containing BtA at concentrations of 0.5, 1, 2, and 4 μg g -1 . The longevity of female and male parasitoids significantly decreased when newly emerged wasps were fed a honey solution containing 200 μg ml -1 BtA in comparison with those fed only a honey solution. Mean longevity was significantly prolonged when parasitoids were fed a honey solution and BtA-honey solution in comparison with those fed BtA-distilled water, distilled water, or nothing. There were no significant differences compared with the control in any biological characteristics for the offspring of female parasitoids fed the honey solutions containing BtA at concentrations of 50, 100, and 200 μg ml -1 ; characteristics measured include the egg-larval period, pupal weight, male and female pupal periods, adult fresh weight, and adult longevity. When female parasitoids parasitized host larvae that had been fed the diet containing BtA, their male and female pupal periods were significantly prolonged compared with the control (without BtA).