Ecotoxicological effect of insecticides on Ooencyrtus nezarae (Hymenoptera: Encyrtidae) an encyrtid parasitoid of Riptortus pedestris (Hemiptera: Alydidae)

Due to increased field occurrence of Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) on various crops including soybean, persimmon, and apple in recent years in Korea, demand for insecticide application to control the stink bug has become higher. Acute toxicity of eight pesticides on Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), a major egg parasitoid of R. pedestris, was compared in the laboratory. Fenitrothion, spinosad, cyfluthrin, etofenprox, and carbosulfan caused 100% mortality of O. nezarae within 24 hours by topical application or exposure to residue. Fenitrothion was also highly toxic to the parasitoid when ingested orally. In a previous study, release of refrigerated non-viable eggs of R. pedestris was found to increase field parasitism, and thus we evaluated the sublethal effect of fenitrothion when O. nezarae parasitize refrigerated or unrefrigerated host eggs. Although parasitism rate on both kinds of eggs significantly decreased when O. nezarae were provided with host eggs sprayed with fenitrothion, no difference in parasitism rate, adult emergence, sex ratio, development time, and longevity of O. nezarae was found between the refrigerated or unrefrigerated host eggs when the insecticide was treated either before or after oviposition. There was no significant sublethal effect when parasitized host eggs were treated with the insecticide. From these results, all the insecticides tested showed high acute toxicity against O. nezarae with relatively lower sublethal effects. Also refrigeration of host eggs does not affect the susceptibility of O. nezarae to insecticide.