Sublethal effects of four insecticides on Anagrus nilaparvatae (Hymenoptera: Mymaridae), an important egg parasitoid of the rice planthopper Nilaparvata lugens (Homoptera: Delphacidae)

Abstract

The egg parasitoid, Anagrus nilaparvatae (Pang et Wang) (Hymenoptera: Mymaridae), has been considered an important biocontrol agent of Nilaparvata lugens (Stål) (Homoptera: Delphacidae). Laboratory bioassays were set up to examine the sublethal effects of four insecticides, triazophos, deltamethrin, chlorantraniliprole and pymetrozine on A. nilaparvatae through contact routes. The results indicated that the sublethal concentrations (LC20 and LC10) of triazophos and deltamethrin disrupted the ability of A. nilaparvatae to perceive host–plant odor cues. After exposure to sublethal concentrations of triazophos and deltamethrin, some surviving parasitoids showed no response to volatiles from N. lugens-infested plants, and responsive survivors were equally attracted to volatiles emitted from N. lugens-infested plants and those from healthy plants. However, sublethal concentrations (the recommended field rate and half the recommended field rate) of chlorantraniliprole and pymetrozine had little impact on the foraging ability of A. nilaparvatae. More than 90% of surviving A. nilaparvatae responded to volatiles from N. lugens-infested plants, and responsive individuals were significantly attracted by host-associated odors. Surviving A. nilaparvatae exposed to sublethal concentrations of triazophos, deltamethrin, chlorantraniliprole or pymetrozine had a similar behavioral response to kairomones from N. lugens, compared with untreated parasitoids. Parasitism rate of N. lugens eggs by insecticide-treated A. nilaparvatae did not differ significantly from the untreated control. Our results suggested that the foraging ability of A. nilaparvatae was disrupted by the broad-spectrum neurotoxic insecticides triazophos and deltamethrin but not by chlorantraniliprole or pymetrozine, which belong to novel classes of insecticides with distinct modes of action. However, sublethal concentrations of triazophos or deltamethrin did not affect the behavioral response of surviving A. nilaparvatae to host kairomone. The mechanism resulting in the different behavioral responses of surviving A. nilaparvatae remains unknown and should be further studied.