Toxicity of Lavandula angustifolia oil constituents and spray formulations to insecticide-susceptible and pyrethroid-resistant Plutella xylostella and its endoparasitoid Cotesia glomerata

Abstract

Background: Plutella xylostella is one of the most serious insect pests of cruciferous crops. This study was conducted to determine the toxicity of 21 constituents from Lavandula angustifolia essential oil (LA-EO) and another 16 previously known LA-EO constituents and the toxicity of six experimental spray formulations containing the oil (1-6gL-1 sprays) to susceptible KS-PX and pyrethroid-resistant JJ-PX P. xylostella larvae, as well as to its endoparasitoid Cotesia glomerata adults. RESULTS: Linalool and linalool oxide (LC50 = 0.016mgcm-3) were the most toxic fumigant compounds and were 10.7-fold less toxic than dichlorvos to KS-PX larvae. Either residual or fumigant toxicity of these compounds was almost identical against larvae from either of the two strains. Against C. glomerata, dichlorvos (LC50 = 7×10-6mgcm-3) was the most toxic insecticide. LA-EO was ∼1430 times less toxic than dichlorvos. The oil applied as 6gL-1 spray and emamectin benzoate 21.5gL-1 emulsifiable concentrate provided 100% mortality against larvae from either of the two strains. CONCLUSION: Reasonable P. xylostella control in greenhouses can be achieved by a spray formulation containing the 6gL-1 oil as potential contact-action fumigant.