The Bionomics of Sitona scissifrons (Coleoptera: Curculionidae) and its Parasite Microctonus sitonae (Hymenoptera: Braconidae)

Abstract

Sitona scissifrons Say, a predominantly brachypterous weevil, is restricted to vetch, Viccia cracca L., in the Belleville, Ontario, area, though recorded in the literature from various cultivated legumes. Its life history and habits are described. Oviposition was completed by June, and the weevil population declined as a result of natural mortality. New generation weevils, in July and August, usually did not oviposit though many were fertilized before overwintering. A euphorine parasite, Microctonus sitonae Mason, has an overwintered and a midsummer generation that are closely integrated to the univoltine life cycle of S. scissifrons. The population level of the overwintering parasite did not exceed 6 parasites per 100 weevils; that of the mid-summer generation, which also develops in overwintered weevils, was from 33 to 40 parasites per 100 weevils. Factors affecting parasite abundance are discussed; and of these, poor synchronization with the summer-emerged weevils is considered important. Weevil populations were not found to be controlled by the parasites. The immature stages of M. sitonae are compared briefly with those of Centistes lituratus (Haliday), which also parasitizes S. scissifrons and which is here reported from North America for the first time.