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 num bers 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 tot al volatile fractions derived from crushed cotyledons and its three ma jor components, 2-(E)-hexenal, 1-octen-3-ol, and 1-octen-1-one, were t ested 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 mos t effective. Mites were repelled by higher concentrations of the metab olites and 1-octen-3-one, the most active, killed mites at high concen trations. Fewer mites aggregated on DGI007 (resistant) than on Dalkeit h (susceptible) cotyledons treated with droplets of the metabolites. T he three volatile metabolites were recovered from the headspace of und amaged and of damaged cotyledons. Crushed cotyledons of Dalkeith produ ced higher levels of 2-(E)-hexenal and lower levels of 1-octen-3-one t han undamaged cotyledons. The results suggest that damage-induced meta bolites enhance the aggregation of redlegged earth mites at low concen trations and reduce aggregation at high concentrations.