Toxicity of chemical pesticides commonly used in maize to Trichogramma ostriniae (Hymenoptera: Trichogrammatidae), an egg parasitoid of Asian corn borer

Abstract

Chemical pesticides are largely applied worldwide for the control of agricultural pests, and often cause lethal and sublethal side effects on natural enemies. To determine the compatibility of chemical pesticides, commonly used by maize growers, with Trichogramma ostriniae, the toxicities of four herbicides (pendimethalin, topramezone, glyphosate, and atrazine), three insecticides (imidacloprid, emamectin benzoate, and ethiofencarb), and three fungicides (propiconazole, benzoyl cyclazole, and difenoconazole) were tested under laboratory conditions, measuring residual toxicity to T. ostriniae adults, their lethal effects on the parasitoid's eggs inside the host egg, and on the reproduction of the parasitoid's female offspring. Three tested pesticides including ethiofencarb, glyphosate, and benzoyl cyclazole were slightly harmful to T. ostriniae adults, whereas the other seven pesticides were moderately harmful. The pesticide residues of ethiofencarb, and emamectin benzoate, showed slightly persistence of toxicity to T. ostriniae adults, in contrast to the remaining pesticides. Glyphosate, emamectin benzoate, imidacloprid, ethiofencarb, and propiconazole were classified as harmless, causing < 30% reduction in emergence rate of wasps from host eggs, while atrazine, pendimethalin, topramezone, benzoyl cyclazole, and difenoconazole were classified as slightly harmful, causing 31-52% reduction in parasitoid emergence rates. Furthermore, the number of eggs subsequently laid by T. ostriniae females that had emerged from parasitized host eggs treated with atrazine was significantly reduced compared to which of untreated parasitized host eggs. No negative effects were observed with atrazine treatment on the emergence rates of F₁ wasps, their wing deformity rates and sex ratios. The data presented here indicate that the safety interval between pesticide applications and releases of T. ostriniae wasps is 2-3 weeks, which provide valuable information in designing a sound maize integrated pest management program that combines chemical pesticide applications with augmentative releases of T. ostriniae wasps.

Keywords: Acute toxicity; Biological control; Chemical pesticide; Integrated pest management; Trichogramma ostriniae.