Essential oil formulations useful as a new tool for insect pest control

Abstract

This study investigated the effects of some essential oils on Limantria dispar (Lepidoptera: Lymantridae, gypsy moth) larvae, one of the most serious pests of cork oak forests. The essential oils were first formulated as oil in water (o/w) emulsions and used in laboratory bioassays to assess their lethal concentration (LC50). Microcapsules containing the most promising oils (Rosmarinus officinalis and Thymus herba-barona) were then prepared by a phase separation process, followed by freeze-drying. The formulations thus obtained, characterized in terms of essential oil content and composition, morphology, storage stability, and release profile, were tested on gypsy moth larvae. The results showed that the tested oils possess interesting larvicidal effects that make them suitable for application in integrated control strategies. The microencapsulation process gave high encapsulation yields (over 98%) with both essential oils, which have different chemical compositions. The microcapsules had toxic effects at a concentration similar to that usually employed for localized treatments with microgranular synthetic pesticides. Toxicity appeared to be maximized when the microparticles adhered to the typical hair structures of several defoliator families. These formulations seem to be able to protect the core material against environmental agents and could be considered for use in controlled drug release systems. The natural active principles they contain could provide an alternative system in insect pest control.