Toxicity of essential oils of Lippia gracilis chemotypes and their major compounds on Diaphania hyalinata and non-target species

Abstract

Essential oils from plants are a viable alternative to the use of synthetic insecticides. However, the bioactivity of these compounds can vary with plant chemotypes, with important implications for pest control and impact on non-target organisms. In the present work, we analyzed the toxicity of essential oils of two chemotypes of Lippia gracilis Schauer (LGRA-106 [thymol chemotype] and LGRA-109 [carvacrol chemotype]) and their major compounds on Diaphania hyalinata Linnaeus, 1767 and the selectivity of these chemotypes on the pollinator bee Apis mellifera Linnaeus, 1758 and the predator wasp Polybia micans Ducke 1904. Both thymol and carvacrol chemotypes were toxic to D. hyalinata (LD50 = 5.90 and 4.56 μg mg−1, respectively). The monoterpenes thymol and carvacrol isolated were around two and five times more toxic than their corresponding chemotypes, respectively. The lethal times estimated for the essential oil to cause mortality in 50% of D. hyalinata populations were less than three hours. The treatments were not selective to A. mellifera and P. micans. The essential oils of L. gracilis chemotypes represent promising sources for the synthesis of new insecticidal molecules.