Nine insecticides, namely, imidacloprid, thiamethoxam, chlorantraniliprole, clothianidin, pymetrozine, ethofenprox, BPMC, endosulfan, acephate, and the product Virtako® (Syngenta; chlorantraniliprole 20%+thiamethoxam 20%) were tested to determine their toxicity to the parasitoid Trichogramma chilonis using an insecticide-coated vial (scintillation) residue bioassay. All the insecticides tested showed different degrees of toxicity to the parasitoid. Thiamethoxam showed the highest toxicity to T. chilonis with an LC 50 of 0.0014 mg a.i. l −1 , followed by imidacloprid (0.0027 mg a.i. l −1 ). The LC 50 values of acephate and endosulfan were 4.4703 and 1.8501 mg a.i. l −1 , exhibiting low toxicity when compared with other insecticides tested. Thiamethoxam was found to be 3,195, 1,395 and 1,322 times more toxic than acephate, chlorantraniliprole and endosulfan, respectively, as revealed by the LC 50 values to T. chilonis. Based on risk quotient, which is the ratio between the field-recommended doses and the LC 50 of the beneficial, only chlorantraniliprole was found to be harmless to T. chilonis. The insecticides thiamethoxam, imidacloprid, Virtako®, ethofenprox and BPMC were found to be dangerous to the parasitoid. Since T. chilonis is an important egg parasitoid of leaf folders, reported to reduce the pest population considerably and often released augmentatively in rice IPM programs, the above noted dangerous chemicals should be avoided in the rice ecosystem.
