Biology of and Host Exploitation by Pleolophus indistinctus (Hymenoptera: Ichneumonidae)

Abstract

Aspects of the biology of Pleolophus indistinctus (Provancher), a parasitoid of cocooned diprionid and tenthredinid sawflies, were studied on 1 host, Neodiprion swainei Middleton, in Quebec Province. Adults emerged from cocoons in June and July, and shortly after, females laid their eggs in host cocoons. Only 4.1% of the progeny emerged in the same year, the remainder overwintered and emerged the following June and July. Adults fed on carbohydrates and animal proteins. The females lived about 4 weeks and during their early life laid an average of 2.2 eggs per day. During oviposition, females destroyed eggs laid by previous females and so eliminated competition. The parasitoid was present in low numbers in every jack pine stand sampled and was recorded from a hardwood stand in 1968 but was not found in black spruce stands. It became the dominant component of the parasitoid complex in low host populations on moist sites. The parasitoid's biology is discussed in relation to factors limiting its population. These factors are the quantity of food available in the host cocoon, the ability of adult parasitoids to discover food and host cocoons, and the duration of host availability.