Monitoring the Methyl Eugenol Response and Non-Responsiveness Mechanisms in Oriental Fruit Fly Bactrocera dorsalis in China

SIMPLE SUMMARY: Bactrocera dorsalis is a highly invasive polyphagous pest of fruit and vegetable, causing severe economic loss and trade restrictions by ovipositing inside hosts. Cryptic feeding habits of larval stages, strong flight ability of adults and prevalence of insecticide resistance reduce the efficiency of chemical control. Currently, the most cost-effective tool is olfaction-based trapping. Methyl eugenol (ME), a naturally occurring compound in some plants, alone or combination with insecticides has been widely used as a male attractant to monitor and control B. dorsalis populations for seven decades. Intense ME selection under laboratory conditions has resulted in the evolution of non- responsiveness in B. dorsalis and field management strategies based on ME has failed to eradicate recolonization of B. dorsalis in some islands. However, the levels of ME responsiveness in B. dorsalis field populations in China is unknown. In this study, we found that field populations had lower ME sensitivity compared to the susceptible strain. Furthermore, the results of olfactory organs, gene expressions and the bioassays showed that odorant binding protein (BdorOBP2, BdorOBP83b) and P450 may be involved in the lower sensitivity. The findings will guide the use of lures combined with insecticides and help to exploit molecular targets for the development of new attractants. ABSTRACT: Bactrocera dorsalis is a notorious polyphagous pest in China, and its management strategies largely depend on methyl eugenol (ME), which has been widely used as an attractant to monitor and eradicate B. dorsalis populations for seven decades. However, the non-responsiveness levels in field B. dorsalis populations to ME is unknown. In this study, we monitored the response to ME in field populations from the four most heavily infested provinces in China, and the results showed that the populations had lower sensitivity to ME relative to GZS susceptible strain. The percent responsiveness of the lowest sensitivity population was 5.88-, 3.47-, and 1.47-fold lower relative to the susceptible strain at doses of 1, 10, and 100 µL of ME, respectively. Gene expression analysis and inhibitor assays further revealed that odorant binding protein (BdorOBP2, BdorOBP83b) and the P450 enzyme system may be associated with the lower response to ME. To our knowledge, this work is the first to report that the P450 enzyme system confers a lower responsiveness to lure insects. These findings provided valuable insights for exploiting ME non-responsiveness to protect sterile males from ME-based control strategies and the use of lures combined with insecticides.