Sublethal Effects of Pyridaben on the Predatory Function of Neoseiulus womersleyi

Abstract

Pyridaben is a widely utilized, broad-spectrum contact acaricide, which has notable sublethal effects that impair the predatory capabilities of predatory mites, but the specific mechanisms that affect the predatory functions remain underexplored. When predatory mites hunt for prey, they may rely on Niemann–Pick-type C2 (NPC2) proteins to collect herbivore-induced plant volatiles (HIPVs) and other odor molecules to locate and pursue their prey. This study elucidated that pyridaben significantly diminished the predatory efficiency and searching behavior of the predatory mite Neoseiulus womersleyi. Key metrics, including predatory capacity (a/Th) and predation rate (a) on various developmental stages of Tetranychus urticae, were markedly reduced in treated mites compared to controls. The searching efficiency (S) also declined proportionally with the increased sublethal dose of pyridaben. A gene linked to olfactive functions, NwNPC2a, was cloned from N. womersleyi. Post-treatment with pyridaben at LC30 and LC50 concentrations resulted in a substantial downregulation of NwNPC2a expression by 60.15% and 58.63%, respectively. Silencing NwNPC2a in N. womersleyi females led to significant reductions in the attack rate (a), handling time (Th), predation efficiency (a/Th), and maximum predation rate (1/Th). The searching efficiency (S) was also lower than that of the control group, displaying a slight decline with the increasing prey density. The findings revealed that pyridaben exerted inhibitory effects on both the predatory function and searching efficiency of N. womersleyi populations. The decrease in predatory performance at LC30 and LC50 concentrations was attributable to the suppression of NwNPC2a gene expression. RNA interference (RNAi) studies corroborated that the NwNPC2a gene plays a critical role in the predation process of N. womersleyi. Thus, the underlying molecular mechanism through which pyridaben compromises the predatory function of N. womersleyi likely involves the downregulation of NwNPC2a expression.