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

Abstract

AbstractA 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.