Repellent and toxic effects of Salvia rosmarinus oil against Liriomyza sativae

Abstract

The vegetable leafminer (VLM) Liriomyza sativae Blanchard is a troublesome pest of vegetable and ornamental plants worldwide. Resistance development and environmental pollution from the overuse of chemical insecticides have driven interest in alternative control strategies for this pest. Secondary metabolites derived from aromatic nonhost plants are recognised components of the plant defence system against herbivores. The essential oils derived from aromatic plants not only repel insects but also have toxic effects against various insect pests, yet little is known about their effects against leafminers. The major constituents of the essential oil extracted from rosemary leaves by hydrodistillation were identified by GC–MS. The behavioural responses of VLM adults to the rosemary essential oil (REO) were explored with Y-tube olfactometer experiments, and the oviposition and feeding deterrent effects of REO against adults were studied using no-choice cage tests. Dipping methods were used to determine the toxicity of REO and Matrine (a commercial botanical pesticide) against VLM eggs, larvae and pupae, while glass-vial bioassays were used for adults. The identified major constituents of the cineoliferum chemotype of REO were 1,8-cineole (23.53%), pinene (23.45%), (S)-(−)-verbenone (12.84%) and borneol (7.47%). REO repelled leafminer adults. Sublethal concentrations of REO deterred oviposition and feeding by adults. Adults were more susceptible than other developmental stages to toxicity of REO and Matrine. Female adults were more sensitive than males, based on EC₅₀ values at 24 and 48 hr after treatment. Rosemary essential oil is a behaviour-modifying stimulus potentially useful in a “push-pull” strategy for L. sativae control, and as an alternative to synthetic chemical insecticides due to its low toxicity and high efficacy in the control of VLM.