Wheat bulb fly, Delia coarctata, larval attraction to phenolic components of host-plant root exudates

Wheat bulb fly (WBF), Delia coarctata Fall en (Diptera: Anthomyiidae), larvae are a subterranean pest of wheat [Triticum aestivum L. (Poaceae)] and other cereals. Larvae locate host plants through chemotaxis and chemokinesis, utilising the primary plant metabolite carbon dioxide as a ‘search trigger’ and Poaceae-specific secondary plant metabolites exuded from the plant. The aim of this study was to use arena bioassays to identify further compounds involved in the host-finding process. The larval behavioural response to four concentrations of syringic and vanillic acid, chemical constituents of host-plant exudates, were tested. Analysis of the final resting position of D. coarctata larvae by the Rayleigh test of uniformity identified attraction to wheat seedling exudates and to both compounds at the lowest concentrations tested, with syringic acid concentrations being most attractive at 0.1 mg l 1 and vanillic acid being most attractive at 0.001 mg l 1. These results add more detail to the subterranean chemical ecology of this species, allowing a behavioural sequence for host-plant orientation byWBF larvae to be proposed.