Optimization of a 4-component chemical attractant for spotted wing drosophila isolated from fermented bait headspace

The invasive spotted wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae), is a serious threat to soft-skinned fresh fruits in US and Europe.  We sought to improve a 4-component chemical attractant, composed of acetic acid, ethanol, acetoin and methionol, by optimizing the amounts of each of the four attractant components.  Within the tested ranges, we found logarithmic increases in SWD trapped with increases in the release of acetoin from polyethylene (PE) sachets and also with increases in the doses of acetic acid or ethanol in the trap drowning solution.  We saw no such increase in SWD trapped with increases in methionol.  A new lure with optimized amounts of acetoin and methionol dispensed from individual PE sachets and acetic acid and ethanol in the trap drowning solution, yielded two times more SWD trapped than a prior reported lure system.  Further field testing showed that simultaneous increases in the release of acetoin and the dose of acetic acid are essential to get an increased fly trap response.  This new optimized formulation is an improvement over the prior reported lure formulation, and should be of greater use in efforts to detect and monitor SWD.