Field capture of northern and western corn rootworm beetles relative to attractant structure and volatility

We used field assays to study attraction of feral northern and western corn rootworm beetles (Diabrotica barberi and D. virgifera virgifera) to a series of mostly nitrogenous and benzenoid synthetic compounds allied with host plant and floral aromas. Vaporization rates were obtained for most field-tested compounds and selected additional lures under both ideal and field-representative, but constant, conditions. Although many test compounds showed at least trace activity for one or both species, methyl benzoate and some of its derivatives, notably methyl anthranilate and methyl 4-methoxybenzoate, merited emphasis as effective new lures for females. Structural alteration of methyl benzoate had consistently negative effects on northern corn rootworm captures despite variable effects on release rate, whereas western corn rootworm was more strongly attracted to methyl anthranilate and methyl 4-methoxybenzoate than to the considerably more volatile parent compound. Phenylacetaldoxime was attractive to females of both species, but no more so than syn-benzaldoxime, included as reference. Release rate was disproportionately low for benzaldoxime, as well as other nitrogenous lures, under field compared with ideal conditions. The attractiveness of salicylaldoxime to northern corn rootworm, despite its low field release rate, and the unattractiveness of methyl salicylate, having a methyl ester in place of the oxime group, similarly highlighted importance of the oxime moiety for reactivity of this species.