The insecticidal toxicity of thymol and carvacrol to brown planthopper and the novel control strategy based on their disruption of the cuticular hydrophobicity

Abstract

The brown planthopper (Nilaparvata lugens (Stål)) is a major pest in rice cultivation. Due to its rapid reproduction and quick resistance development, current control strategies rely heavily on chemical insecticides. This has led to resistance in brown planthoppers to various commonly used insecticides. The limitations of traditional chemical control methods highlight the urgent need for environmentally friendly and sustainable alternatives. This study evaluated the contact toxicity, fumigant toxicity, and spray treatment effects of thymol, carvacrol, and five other volatile compounds against N. lugens nymphs. Results showed that thymol and carvacrol exhibited the strongest insecticidal effects. Both the two compounds, derived from plant essential oils, are low in toxicity and significantly disrupted the hydrophobicity of the nymphs' cuticles, converting them from hydrophobic to hydrophilic. Spray experiments further confirmed their insecticidal efficacy, and rinsing N. lugens after spray treatment with both compounds significantly increased N. lugens mortality rate. GC–MS analysis revealed interactions between carvacrol and cuticular hydrophobic compounds, such as octyl palmitate. These findings suggest that thymol and carvacrol could serve as effective green bioinsecticides by targeting the cuticle and internal compounds of N. lugens. In this study, a novel pest control strategy for rice field pests such as N. lugens was proposed, aiming to disrupt their cuticular hydrophobicity, thereby preventing them from escaping when falling into water and leading to drown in the field water. This method holds promise for significantly reducing the dependence on toxic pesticides and lowering pesticide usage.