Laboratory Safety Evaluation Of Insecticides To Trichogramma Japonicum Ashmead (Hymenoptera: Trichogrammatidae), An Egg Parasitoid Of Chilo Suppressalis Walker(Lepidoptera: Pyralidae)

Trichogramma japonicum Ashmead (Hymenoptera: Trichogrammatidae), an egg parasitoid, is a common nature enemy in rice paddy and it plays an important role in control of Chilo suppressalis Walker, Tryporyza incertulas Walker and Cnaphalocrocis medinalis Güenée. Safety of insecticides in seven groups to each developmental stage of T. japonicum was evaluated under the laboratory conditions in this text.Safety of 29 insecticides in 7 classes to adult wasps of T. japonicum developing in eggs of Corcyra cephalonica Stainton was evaluated by means of toxic film. Buprofezin, chlorfluazuron, tebufenozide, JS 118 and hexaflumuron (IGRs) were safe to adult, and they had the lower toxicity, with their LC₅₀＞1000 mg a.i./L; while thiamethoxam, isoprocarb, chlorpyrifos, diazinon, phoxim and imidacloprid were extremely unsafe to adult, and they had the higher toxicity, with their LC₅₀ 0.014 - 0.089 mg a.i./L. Furthermore, the safety of methamidophos and triazophos to T. japonicum developing in the eggs of Chilo suppressalis Walker was compared with that of these two insecticides to T. japonicum developing in the eggs of Corcyra cephalonica Stainton, which showed that the latter was superior to the former.Buprofezin, tebufenozide, JS118 and hexaflumuron had no effects on survival and parasitism capacity of adults exposed to leaf residues at various intervals after treated with insecticides. Fipronil, thiamethoxam, chlorpyrifos and triazophos had the most effects on adult survival, and 2-and 7-day-old residues caused 100% and 80.0% to 98.9% mortality respectively. Seven-day-old residues of fipronil and triazophos had no significant effects on parasitism capacity, but thiamethoxam did.The results of host egg exposure showed that imidacloprid, triazophos, fipronil and chlorpyrifos were all badly detrimental to adult survival, parasitism capacity (F₀) and adult emergence (F₁), while buprofezin, tebufenozide, JS118 and hexaflumuron had no effects on survival and parasitism capacity of F₀ and F₁ adults. Emamectin benzoate was harmless to F₀ adults, but it was slightly harmful to F₁ adults with reference to parasitism capacity. Thiamethoxam had moderately harmful effects on survival of F₀ adults, slightly harmful effects on parasitism capacity of Fo adults, and harmless effects on survival and parasitism capacity of F₁ adults.When dipping parasitized host eggs, in which the Trichogramma japonicum was at different stages of immature development (egg, larvae, prepupae and pupae), into insecticidal solutions, buprofezin, tebufenozide and JS 118 were found to have little effect on adult emergence, with 81.4-91.8% emergenees of the adult; hexaflumuron, emamectin benzoate and thiamethoxam were selective, hexaflumuron was harmless to pupae, emamectin benzoate was harmless to egg and pupae, and thiamethoxam was harmless to egg. Methamidophos was moderately harmful to these four stages, which resulted in 18.5-39.6% adult emergence. Imidacloprid, triazophos, fipronil, ehlorpyrifos, dichlorvos and isoprocard significantly lowered adult emergence when tested against any immature stage. They were all below 10%. With reference to adult longevity, buprofezin, tebufenozide and JS118 were harmless to adults emerging from any developmental stage treated with insecticides, while emamectin benzoate and thiamethoxam were slightly harmful.Based on the results from our study, the IGRs buprofezin, tebufenozide and JS118 were not directly or indirectly harmful to T. Japonicum, so these insecticides are compatible with this parasitoid when used for control of rice pests.