Toxicity and Sublethal Effect of Farnesyl Acetate on Diamondback Moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae)

SIMPLE SUMMARY: The diamondback moth, Plutella xylostella, is the most destructive pest for Brassica vegetable crops worldwide. The management of this pest was estimated to cost about United States dollars (USD) 4–5 billion annually. Prolonged and unsupervised insecticide exposures have led to not only the emergence of insecticide resistance in P. xylostella, but also negative impacts on human health, environmental pollution, and nontargeted organisms. Therefore, the development of new safer, environmentally friendly, and target-specific insecticides is vital in order to combat this pest. In this study, we evaluated the potential of selected farnesyl derivative compounds that could act as biorational insecticides targeting the juvenile hormone biosynthesis of P. xylostella. Out of five farnesyl derivatives tested, farnesyl acetate showed the highest mortality percentage of P. xylostella. Then, the sublethal effects of farnesyl acetate on biological characteristics of P. xylostella were determined. The results demonstrated that farnesyl acetate had negative effects on development, pupal weight, pupation, adult emergence, female ratio, fecundity, egg hatching rate, and oviposition period of P. xylostella. Farnesyl acetate also induced abnormalities in pupal and adults of P. xylostella. These findings indicate that farnesyl acetate can reduce the population number and reproductive success of P. xylostella, possibly leading to the effective management of this pest. ABSTRACT: The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is the most important pest of cruciferous vegetables worldwide. In this study, we evaluated the properties of selected farnesyl derivative compounds against P. xylostella. The toxicity and sublethal concentration (LC(50)) of farnesyl acetate, farnesyl acetone, farnesyl bromide, farnesyl chloride, and hexahydrofarnesyl acetone were investigated for 96 h. The leaf-dip bioassays showed that farnesyl acetate had a high level of toxicity against P. xylostella compared to other tested farnesyl derivatives. The LC(50) value was 56.41 mg/L on the second-instar larvae of P. xylostella. Then, the sublethal effects of farnesyl acetate on biological parameters of P. xylostella were assessed. Compared to the control group, the sublethal concentration of farnesyl acetate decreased pupation and emergence rates, pupal weight, fecundity, egg hatching rate, female ratio, and oviposition period. Furthermore, the developmental time of P. xylostella was extended after being exposed to farnesyl acetate. Moreover, the application of farnesyl acetate on P. xylostella induced morphogenetic abnormalities in larval–pupal intermediates, adults that emerged with twisted wings, or complete adults that could not emerge from the cocoon. These results suggested that farnesyl acetate was highly effective against P. xylostella. The sublethal concentration of farnesyl acetate could reduce the population of P. xylostella by increasing abnormal pupal and adults, and by delaying its development period.