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

Authors: Tabanca, Nurhayat; Cloonan, Kevin; NESTERKINA, MARIIA - Helmholtz Centre; Gill, Micah; Montgomery, Wayne; KRAVCHENKO, IRYNA - Helmholtz Centre; KENDRA, PAUL - Retired ARS Employee

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2024
Publication Date: 8/3/2024
Citation: Tabanca, N., Cloonan, K.R., Nesterkina, M., Gill, M.A., Montgomery, W.S., Kravchenko, I., Kendra, P.E. 2024. Behavioral and electrophysiological responses of the male medfly, Ceratitis capitata, to thymol and carvacrol ethers. Pest Management Science. https://doi.org/10.1002/ps.8324.
DOI: https://doi.org/10.1002/ps.8324

Interpretive Summary: Fruit flies are the most important pest of fruits and vegetables worldwide. Mediterranean fruit fly, or medfly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is a quarantine pest in the United States. The most effective method of control is the sterile insect technique (SIT) in which a large number of sterilized males are released into the wild population and mate with wild females. Chemical signals are the most important factor for insect–plant interactions and profoundly affect insect behavior and physiology. Currently, medfly detection and monitoring programs rely on the parapheromone trimedlure (TML), a male-specific attractant. However, the cost and limited availability of TML has prompted a search for the identification of alternative attractants. A combination of laboratory bioassays and electroantennographic analyses were conducted to quantify behavioral and olfactory responses of new potential medfly attractants. Thymol benzyl and octyl ethers, and carvacrol benzyl ether evoked significantly greater antennal responses than thymol or carvacrol. Future study will require testing these compounds in long-range attraction assays. This study revealed some key structural features responsible for attraction, information that will benefit future researchers in the development of improved lures for Mediterranean fruit fly.

Technical Abstract: BACKGROUND: 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. 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. RESULTS: In short-range attraction bioassays, parent compounds, thymol and carvacrol, along with their propyl, butyl, benzyl, and octyl ethers captured more male C. capitata. The patterns change over time, and captures are only sign if greater than tea tree oil(TTO) at 90 min, and not with all ethers either. In EAG assays, thymol benzyl and octyl ethers, and carvacrol benzyl ether evoked significantly greater antennal responses than their parent compounds. The electroantennography (EAG) responses did not correlate with short-range male attraction. The aliphatic side chains of thymol and carvacrol have a small effect on the activity. Future studies will investigate the long-range attraction of the ethers that elicited large EAG responses. CONCLUSION: This report provides new information to discover 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 to tea tree oil (TTO, a strong medfly attractant), with significantly higher captures than TTO observed at 90 min in lab bioassays. Further chemical synthesis of thymol and carvacrol ethers within this series may lead to the development of more attractive or persistent ethers than parent compounds, thymol and carvacrol.