Methyl-isoeugenol, a significantly more attractive male lure for the methyl eugenol-responsive Pacific fruit fly, Bactrocera xanthodes (Diptera: Tephritidae)

Bactrocera xanthodes (Broun) (Dacinae), the Pacific fruit fly, is a major pest that is widespread in the South Pacific. It infests the fruit of 34 hosts in 20 families and is a significant impediment to horticultural market access for South Pacific countries. It is weakly responsive to the male attractant methyl eugenol (ME) and consequently is difficult to detect and control. Recently, in Australia and Bangladesh, some weakly ME-responsive species were found to be more attracted to one or more of the eugenol analogues isoeugenol, methyl-isoeugenol and dihydroeugenol. We therefore considered it worthwhile to field test the relative attractiveness of these lures to B. xanthodes. Field trials were conducted in Tonga for 9 weeks between September and November 2017. The male attractants isoeugenol, methyl-isoeugenol, dihydroeugenol and a novel eugenol analogue, 1,2-dimethoxy-4-propylbenzene, were tested in comparison to ME, cue-lure and zingerone. More than three times more male B. xanthodes were caught in methyl-isoeugenol-baited traps (mean 33.0 +/- 1.8 flies/trap/day(FTD)) than in ME traps (10.7 +/- 1.0 FTD) with several individual weekly methyl-isoeugenol trap clearances catching over 600 flies. Bactrocera xanthodes was also caught in 1,2-dimethoxy-4-propylbenzene traps (mean 3.1 +/- 0.5 FTD), but in numbers significantly less than in ME. This is the first record of this species responding to these novel male lures. The significantly greater response of B. xanthodes to methyl-isoeugenol would make it a considerably more effective attractant for use in surveillance and control programs.