Electroantennogram responses of six Bactrocera and Zeugodacus species to raspberry ketone analogues

Abstract

Environmental context. Queensland fruit fly is a major pest of fruits and vegetables in eastern Australia, sometimes causing complete loss of unprotected crops. Odours that attract fruit flies can help control these pests and this study investigated how six fruit fly species smell these chemicals. The strength of fly responses to tested odours gives insight into the way flies smell and provides information for making better attractants, potentially reducing insecticide use.. The Queensland fruit fly (Bactrocera tryoni, Q-fly) is a major horticultural pest in eastern Australia. The deployment of male lures comprises an important component of several detection and control strategies for this pest. A novel fluorinated analogue of raspberry ketone (RK), raspberry ketone trifluoroacetate (RKTA), has been developed with the aim of further improving Q-fly control. RKTA elicited strong electroantennogram (EAG) responses from Q-flies whereas cuelure (CL) and melolure (ML) responses were not significantly greater than a negative control. Further experimentation showed that RKTA also elicited EAG response from five other fruit fly species, included flies known to be strongly attracted to CL (B. neohumeralis, B. kraussi and B. frauenfeldi), weakly attracted to CL (B. jarvisi), or non-responsive to CL (Zeugodacus cucumis), whereas seven other compounds, RK, CL, ML, raspberry ketone difluoroacetate, raspberry ketone monofluoroacetate, anisyl acetone and trimethylsilyl raspberry ketone, elicited only weak responses comparable with a negative control. However, fly EAG responses to RKTA are likely due at least in part to trifluoroethanoic acid, which is a hydrolysis product of RKTA and elicited strong EAG responses from all six species when tested alone. Furthermore, whereas ethanoic acid, methanoic acid and trifluoroethanoic acid all elicited strong EAG responses in Q-flies, the only corresponding RK ester to elicit an EAG response was RKTA, suggesting that RKTA hydrolyses quickly, whereas CL and ML do not. This is in contrast to the idea that CL readily hydrolyses on contact with atmospheric moisture, an assertion that has been made in the literature repeatedly.