Terpene- and alcohol-based attractants for the Mediterranean fruit fly isolated from tea tree oil

Trimedlure (TML), a synthetic male-specific parapheromone, is the standard lure used to monitor the Mediterranean fruit fly, or medfly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), an economically important pest of fruit crops worldwide. The Animal and Plant Health Inspection Service (APHIS) deploys thousands of TML-baited traps in the USA to monitor C. capitata populations. Although TML is an effective attractant, it has a relatively short field life, is expensive, and is supplied by only one manufacturer creating a need for TML-alternatives. As part of an effort to identify new attractants, we developed a thin-layer chromatography (TLC) method for separating and assaying fractions of tea tree essential oil (TTO) that are attractive to male medflies. Five distinct TTO fractions were separated initially and two were found to attract males. In the current study, we used gas chromatography coupled with electroantennographic detection (GC-EAD) and gas chromatography coupled with mass spectrometry (GC-MS) to identify four antennally-sensitive monoterpenes from fraction 1, and two alcohols from fraction 3. Electroantennography (EAG) assays quantified the olfactory responses to volatile emissions from synthetic EAD-active compounds. Small-cage bioassays indicated that the two alcohols were more attractive than TTO and that the four monoterpenes were less attractive than TTO. The addition of one monoterpene, however, to the alcohols increased attraction compared to either alcohol alone, and male flies spent more time contacting and clustering around this monoterpene than TTO or the two alcohols. Alternatives to TML for monitoring medfly populations could reduce programs costs involved in managing this serious agricultural pest.