Evaluating Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) Response to Methyl Eugenol: Comparison of Three Common Bioassay Methods.

Insect responses to chemical attractants are often measured using olfactory bioassays prior to testing in field experiments. The attraction of sexually mature male Bactrocera dorsalis to methyl eugenol (ME) and the loss of attraction by ME pre-fed males have been demonstrated in laboratory bioassays and field trapping studies. It has been suggested that ME nonresponsiveness can be exploited to improve the effectiveness of B. dorsalis management programs by protecting sterile males from ME-based control measures. Currently, work is underway to identify alternatives that reduce or eliminate ME response. To support the development of compounds and evaluation of their effect on B. dorsalis attraction to ME, we compared the effectiveness of three common bioassay methods that have been used to measure lure response in Bactrocera flies under controlled conditions (choice assays using Y-tube [Y], small-cage arena [SC], and rotating carousel field-cage [RC]) to determine which bioassay method is efficient and reliable. A series of bioassays comparing ME-exposed and ME-naïve wild-type and genetic sexing strain males showed that the RC and SC were effective at both observing attraction to ME and detecting a significant reduction in ME response from ME-exposed males. However, the male attraction to ME and a significant decrease in response to ME after ME feeding was not observed in our Y-tube assays. These suggest that RC and SC are preferable options to evaluate ME non-responsiveness in B. dorsalis, and that Y-tube tests are difficult to administer correctly.