Exploring the Efficacy of Four Essential Oils as Potential Insecticides against Thrips flavus

Plant essential oils are important alternatives in green integrated pest management. This study examined the chemical composition, bioactivity, and control efficacy of four Lamiaceae essential oils (EOs) against Thrips flavus Schrank in laboratory conditions with the goal of exploiting plant-derived insecticides to control Thrips flavus. The four EOs tested were marjoram oil (Origanum majorana L.), clary sage oil (Salvia sclarea L.), perilla leaf oil (Perilla frutescens (L.) Britt.), and spearmint oil (Mentha spicata L.). All these EOs exhibited a certain degree of insecticidal activity against Thrips flavus. The median lethal concentration (LC₅₀) was determined after treatment by the leaf-dipping method in laboratory bioassays, and its values were 0.41 mg/mL for marjoram oil, 0.42 mg/mL for clary sage oil, 0.43 mg/mL for perilla leaf oil, and 0.54 mg/mL for spearmint oil. In the pot experiment, the number of dead insects was recorded at 1, 3, and 7 days post-application, and the control efficacy of EOs against Thrips flavus was calculated. The concentration of 900.00 g a.i.·hm⁻² of spearmint oil was 100% lethal against Thrips flavus after treating potted plants for seven days. The Y-tube olfactometer method was used to test for the attraction or repellent response of EOs against Thrips flavus. The spearmint oil significantly attracted female adults in the olfactory test. Furthermore, gas chromatography–mass spectrometry (GC–MS) was used to examine the chemical composition of the EOs. Linalool (24.52%), isopropyl myristate (28.74%), (+)-limonene (32.44%), and (+)-carvone (70.3%) were their primary ingredients. The findings suggest that all four EOs are highly effective against Thrips flavus and may be a possible alternative in the management of Thrips flavus, especially when considering reducing the use of synthetic pesticides.