Experimental Host Preferences of Monoctonus paulensis (Hymenoptera: Braconidae), including a Hypothetical Scheme of Host Selection

Abstract

When offered a choice of 5 known dactynotine host species in cage experiments, the aphidiine parasite, Monoctonus paulensis (Ashmead), did not exhibit a distinct preference for a particular species, but parasitized them all with equal frequency. Further tests, utilizing Pyrex® tubes, exposed 2 pairs of aphid hosts to parasite attack, i.e., Acyrthosiphon pisum (Harris) and Therioaphis trifolii (Monell), and Sitobion fragariae (Walker) and Rhopalosiphum padi (L.). The 1st member of each pair was a known host in the Dactynotini, the other species belonged to a different aphid group and was not known to be an acceptable host. Female parasites did not display a preference for attacking S. fragariae in favor of R. padi in these tests, but did prefer A. pisum nymphs to those of T. trifolii . Nymphs of R. padi and T. trifolii were found to be physiologically unsuitable hosts. The results of these tests, combined with field data obtained in an earlier study, were used to depict the host-selection process of this parasite species as it probably occurs in the field.