The Effect of Volatile Metabolites of Lipid Peroxidation on the Aggregation of Redlegged Earth Mites Halotydeus destructor (ACARINA: PENTHALEIDAE) on Damaged Cotyledons of Subterranean Clover

Redlegged earth mites (Halotydeus destructor) aggregated in larger numbers on cotyledons of subterranean clover (Trifolium subterraneum L.) previously damaged either by mite feeding or by mechanical injury than on undamaged cotyledons. This effect lasted for up to 7 days. The total volatile fractions derived from crushed cotyledons and its three major components, 2-(E)-hexenal, 1-octen-3-ol, and 1-octen-1-one, were tested for their effect on the aggregation of mites. Significantly more mites gathered on detached cotyledons treated with the metabolites at low concentrations than on controls, with 2-(E)-hexenal being the most effective. Mites were repelled by higher concentrations of the metabolites and 1-octen-3-one, the most active, killed mites at high concentrations. Fewer mites aggregated on DGI007 (resistant) than on Dalkeith (susceptible) cotyledons treated with droplets of the metabolites. The three volatile metabolites were recovered from the headspace of undamaged and of damaged cotyledons. Crushed cotyledons of Dalkeith produced higher levels of 2-(E)-hexenal and lower levels of 1-octen-3-one than undamaged cotyledons. The results suggest that damage-induced metabolites enhance the aggregation of redlegged earth mites at low concentrations and reduce aggregation at high concentrations.