ASSAYS FOR THE EFFECTS OF VOLATILE COMPOUNDS FROM ARTIFICIALLY DAMAGED COTYLEDONS OF SUBTERRANEAN CLOVER ON THE REDLEGGED EARTH MITE, HALOTYDEUS DESTRUCTOR

The effects on the redlegged earth mite (Halotydeus destructor) (Acari na: Penthaleidae) of volatile compounds released from artificially dam aged cotyledons of subterranean clover (Trifolium subterraneum L.), a host plant, were investigated with different assays. Mites were repell ed by the volatile compounds in flask tube and in trimmed cotyledon di sc tests. No differences could be shown between different tissue amoun ts and between resistant and susceptible varieties. When a membrane sa chet was used containing either 2-(E)-hexenal, a compound produced by damaged subclover cotyledons, or the total volatile compounds collecte d from damaged cotyledons of Dalkeith (susceptible) admired with 1% gl ucose, mites gathered to low but were deterred by high concentrations of the compounds. Volatile compounds collected from the resistant vari ety DGI007 were more deterrent than those from the susceptible Dalkeit h. Membrane sachets containing 30 p.p.m. of 2-(E)-hexenal and 1% gluco se were less preferred than cotyledons of Dalkeith (susceptible) but w ere not different from DGI007 (resistant). By increasing the glucose c oncentration to 5%, the membrane sachets with 30 p.p.m. of 2-(E)-hexen al were preferred to cotyledons of either variety. The results indicat e that the membrane feeding technique provides a sensitive way of assa ying volatile compounds from damaged subclover cotyledons against the mite.