Behavioral and electrophysiological responses of the male medfly, Ceratitis capitata, to thymol and carvacrol ethers

The Mediterranean fruit fly, Ceratitis capitata, is one of the most economically important insect pests attacking fruits and vegetables in tropical and subtropical areas of the world. Semiochemical-based pest management programs are being used to provide environmentally friendly control methods for medflies. The goals of the current study were to discover potential new, attractive, kairomones by designing, synthesizing, and testing simplified ethers of thymol and carvacrol along with their ether derivatives in short-range attraction assays and electroantennogram (EAG) assays with male C. capitata. To the best of our knowledge, this study represents the first investigation of thymol and carvacrol, and their respective ethers for attractancy to C. capitata, a major agricultural pest worldwide.

In short-range attraction bioassays, parent compounds, thymol and carvacrol, along with their propyl, butyl, benzyl, and octyl ethers captured the most male C. capitata. The attraction patterns changed over time and captures were only significant if they were greater than the positive control tea tree oil (TTO) at 90 min. In EAG assays, thymol benzyl, octyl ethers, and carvacrol benzyl ether evoked significantly greater antennal responses than their parent compounds. The EAG responses did not correlate with short-range male attraction. The aliphatic side chains of thymol and carvacrol had a small effect on the activity. Future studies will investigate the long-range attraction of the ethers that elicited large EAG responses.

This report provides new information for discovering potential kairomones through synthesis and structure-activity studies for sterile male medflies. Thymol, carvacrol, and several of their ether derivatives displayed improved longevity of attraction compared with TTO (a strong medfly attractant), with significantly higher captures than TTO observed at 90 min in laboratory bioassays. Further chemical synthesis of thymol and carvacrol ethers within this series may lead to the development of ethers that are more attractive or persistent than their parent compounds, thymol and carvacrol. © 2024 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.