6-METHYL-5-HEPTENE-2-ONE, A PUTATIVE SEX AND SPACING PHEROMONE OF THEAPHID HYPERPARASITOID, ALLOXYSTA-VICTRIX (HYMENOPTERA, ALLOXYSTIDAE)

Hyperparasitoids are, considered to reduce the effectiveness of primar y parasitoids as biological control agents of aphids in a variety of c rops. Recently it was shown that volatiles produced by the hyperparasi toid Alloxysta victrix (Westwood) elicit a dispersal in female primary parasitoids thereby potentially reducing primary parasitoid activity in the field at certain times. The active chemical was identified as 6 -methyl-5-heptene-2-one (MHO) which is produced by both male and femal e A. victrix. The function of this chemical in the intraspecific commu nication of A. victrix was studied. Y-tube olfactometer experiments re vealed corresponding effects of MHO and natural odour sources. Males w ere attracted to females especially when not mated. Females were repel led by females. These effects could partly be mimicked with pure MHO i n the olfactometer. In Petri dish experiments the behaviour of A. vict rix in the presence of MHO odour was video-analysed. As in the olfacto meter, males were attracted to the odour and females repelled. We conc lude that MHO is a sex pheromone which attracts A. victrix males and a s spacing pheromone enables an even distribution of females in the fie ld.