Formation of lipoxygenase products in Phaseolus vulgaris L. leaves as a response to twospotted spider mite (Acari: Tetranychidae) feeding and their effect on spider mite populations

We investigated volatile emission from horticultural dwarf bush bean leaves in response to either mechanical wounding or feeding by adult twospotted spider mites, Tetranychus urticae Koch. After treatment (mechanical wounding or mite feeding) leaflets were incubated in glass vials. Air samples from the vials were then analyzed by gas chromatography. The principal volatiles detected with our system were${\rm C}_{6}\text{-aldehydes}$which is consistent with lipoxygenase-mediated peroxidation of polyunsaturated fatty acids induced by the damage. A biochemical model is proposed to explain this result. Experimental arenas were then used to expose mites to a range of concentrations of these aldehydes from those concentrations found in the above trial to 10-fold greater concentrations. Both mortality and reduced fecundity were observed at the highest concentrations of hexanal and trans-2-hexenal but only fecundity was affected at lower concentrations. These results were consistent with our model and other reports that this inducible response mechanism only affects mite fecundity when spider mites are used as the eliciting stimulus.