Susceptibility of adult Trichogramma nubilale (Hymenoptera: Trichogrammatidae) to selected insecticides with different modes of action

The parasitic wasp Trichogramma nubilale (Hymenoptera: Trichogrammatidae) is one of the most suitable parasitoids for controlling Asian corn borer, Ostrinia furnacalis (Lepidoptera: Crambidae). Although extensive toxicological tests have been carried out to elucidate the toxicities of insecticides to trichogrammatids, the acute toxicity risks of commonly used insecticides to T. nubilale are not well known. Among the 7 classes of tested chemicals, organophosphates and carbamates had the highest intrinsic toxicity to the parasitoid with LC50 values ranging from 0.081 (0.062–0.12) to 2.10 (1.23–3.47) and from 0.12 (0.11–0.14) to 0.95 (0.87–1.05) mg a.i. per liter, respectively. The phenylpyrazoles (with the exception of butene-fipronil), avermectins, neonicotinoids and pyrethroids induced intermediate toxicity responses with LC50 values ranging from 0.29 to 4.67, 2.36 to 11.27, 1.86 to 311.9, and 10.98–150.3 mg a.i. per liter, respectively. In contrast, insect growth regulators (IGRs) exhibited the least toxicity to the parasitoid with LC50 values ranging from 3452 (3114–3877) to 10,168 (8848–12,027) mg a.i. per liter. A risk quotient analysis indicated that neonicotinoids, avermectins, pyrethroids, IGRs and phenylpyrazoles (with the exception of butene-fipronil) were safe, but organophosphates and carbamates were slightly to moderately toxic or highly toxic to T. nubilale. This study provided informative data for implementing both biological and chemical control strategies in integrated pest management (IPM) of corn lepidopterans.

► The toxicities of 30 insecticides to adult Trichogramma nubilale were evaluated.
► The insecticides tested showed different degree of toxicity to T. nubilale.
► Organophosphates and carbamates had the highest intrinsic toxicity to T. nubilale.
► The insect growth regulators exhibited the least toxicity.
► The other four chemical groups induced variable toxicity responses.