Toxic, Oviposition Deterrent and Oxidative Stress Effects of Thymus vulgaris Essential Oil against Acanthoscelides obtectus

SIMPLE SUMMARY: Compounds of botanical origin, including essential oils (EOs), which coevolved as plant defense mechanism against herbivores and pathogens have been proposed as a promising strategy for post-harvest control of stored product insects. Despite several drawbacks, such as low stability, phytotoxicity and food odor changes at high concentrations, EOs are believed to be safe for human and environmental health and thus have an advantage comparing to conventional insecticides. The present study was aimed to examine acute toxicity and effects of thyme (Thymus vulgaris) EO on longevity, behavior and physiology of the bean weevil (Acanthoscelides obtectus), a major pest of stored bean seeds. We found that exposure to thyme oil reduced adult survival and longevity and induced damages to lipids and proteins in a concentration-dependent manner. Sublethal EO concentrations also deterred female egg laying and strongly inhibited adult emergence. Efficacy of such low EO concentrations in suppression of adult emergence implies that thyme EO might be cost-effective and environmentally low risk botanical insecticide for bean seed protection against A. obtectus. ABSTRACT: The bean weevil Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae) can cause significant losses in production of its primary host common bean Phaseolus vulgaris L. To avoid bean protection with environmentally risky chemical insecticides and provide sustainable and safe production of food, new pest management methods based on natural compounds are investigated. In the present study, we evaluated protective potential of the essential oil (EO) from the common thyme Thymus vulgaris L. applied on bean seeds. We assessed residual contact toxicity of thyme EO and its effects on A. obtectus longevity, oviposition and adult emergence. Furthermore, to elucidate the role of oxidative stress in thyme EO toxicity, we estimated the levels of oxidatively damaged proteins and lipids, as well as the level of thiols which have important role for antioxidant capacity. We found that thyme oil significantly reduced adult survival and longevity, induced oxidative damage to lipids and proteins and depleted protein and non-protein thiols in a concentration-dependent manner. Females appeared to be more tolerant to thyme oil treatment than males. Sublethal EO concentrations affected oxidative stress indices, deterred oviposition and strongly inhibited adult emergence. The results suggest that thyme oil has the potential to be used as an ecofriendly insecticide for A. obtectus control.