Abstract:A bioassay was conducted using a drug contacting method to determine the contact toxicities of various pesticides commonly used in the paddy field to female adults of Cotesia chilonis (Matsumura) a larval and dominant endoparasitoid of the rice stem borer Chilo suppressalis (Walker) from four different locations including Yangzhou, Anji, Jinhua and Yueqing. The results indicated that among seven technical productions of insecticides, fipronil, chlorpyrifos and triazophos showed higher toxicity to this parasitic wasp, and monosultap, imidacloprid and avermectin showed the moderate toxicity, while chlorantraniliprole exhibited the lowest toxicity. Among twelve kinds of insecticide preparations, chlorantraniliprole SC and three preparations associated with avermectin had relatively lower toxicity to this parasitic wasp, while others had higher toxic effects. Among four kinds of germicides, tricyclazole-iprobenfos showed the highest toxicity, propiconazol difenoconazole showed moderate toxicity, and both of validamycin and moroxydine hydrochloride-ribavirin showed the lowest toxicity. As regard to two kinds of herbicides, bensulfuron-methyl pretilachlor had the higher toxicity to this parasitic wasp by comparison with quinclorac-bensulfuronmethyl. In addition, the same pesticide had different toxicity to the parasitic wasps depending on their sampled locations at some cases.