Effects of imidacloprid on the orientation behavior and parasitizing capacity of Anagrus nilaparvatae, an egg parasitoid of Nilaparvata lugens
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Anagrus nilaparvatae (Pang et Wang) (Hymenoptera: Mymaridae), is an egg parasitoid of rice planthoppers, Nilaparvata lugens (Stål) (Homoptera: Delphacidae). This study evaluated effects of the insecticide imidacloprid on orientation behavior and parasitizing capacity of A. nilaparvatae. Sub-lethal concentrations of imidacloprid (LC20 and LC10) disrupted the foraging ability of A. nilaparvatae exposed to imidacloprid through contact or oral routes. Some survivors did not respond to volatiles from N. lugens-infested plants. Responsive individuals were equally attracted to volatiles from N. lugens-infested and healthy plants. Volatiles emitted from rice plants treated with a low concentration of imidacloprid were more attractive to A. nilaparvatae than those from plants treated with a high concentration of imidacloprid. Parasitism of N. lugens by A. nilaparvatae that survived contact with sub-lethal concentrations of imidacloprid did not decrease significantly. When A. nilaparvatae were fed imidacloprid-honey mixture, parasitism rates were 1.49% and 0%, respectively, significantly lower than those of the control (9.58%). Parasitism of N. lugens eggs in high concentration of imidacloprid treated rice plants by A. nilaparvatae decreased significantly. These effects involving disturbed foraging ability and reduced parasitizing capacity of A. nilaparvatae indicated that imidacloprid could decrease the performance of this parasitoid.