HABITAT SELECTION BY THE APHID PARASITE<i>DIAERETIELLA RAPAE</i>(HYMENOPTERA: BRACONIDAE) AND HYPERPARASITE<i>CHARIPS BRASSICAE</i>(HYMENOPTERA: CYNIPIDAE)

Abstract

Abstract A suspected chemical means of habitat selection by Diaeretiella rapae , a primary parasite of aphids on crucifer plants, was investigated in the laboratory with the aid of an olfactometer. Females (and, to a lesser extent, males) were found to be attracted by odor to leaves and leaf juices of a crucifer host plant and to dilute solutions of the mustard oil allyl isothiocyanate. Given a choice of aphid colonies ( Myzus persicae ) on leaves of beet (Chenopodiaceae — mustard oils not present) and collard (Cruciferae — mustard oils present), female D . rapae displayed a marked preference to oviposit in aphids feeding on collard. It is concluded that female D . rapae parasites locate their hosts initially by a response to an odor emanating from the aphid host-plant, followed by visual searching. Male D . rapae were attracted by odor from female D . rapae , suggesting the existence of a sex pheromone in this species.Neither males nor females of Charips brassicae , a hyperparasite of D . rapae , were attracted to collard leaves, though females showed apparent attraction to female D . rapae . As with D . rapae , males of C . brassicae are attracted by odor to females of the same species.The host finding behavior of D . rapae is discussed in relation to that of other insect species belonging to the fauna associated with the plant family Cruciferae.