Abstract
A life table of Bessa harveyi (Townsend), a parasite of yellowheaded spruce sawfly, Pikonema alaskensis (Rohwer), was constructed from field samples of eggs, firstinstar maggots, and adults. Major mortality factors of the parasite, in order of importance, were overwintering maggot mortality, superparasitism, egg infertility and sloughing, and fall emergence. Overwintering mortality included flooding, desiccation, freezing, predation, encapsulation by the host, and failure of adult flies to exit host cocoons. No obligatory diapause was detected when B. harveyi maggots were reared in the host at room temperature (21–22°C) and under constant light. The mean time for maggot development was 8.4 days (SE = 0.33). The sex percentage of 151 laboratory-reared puparia was 51.7% females. Total B. harveyi parasitism on P. alaskensis larvae was 16.7% in 1978 and 21.2% in 1979. B. harveyi is not well adapted to P. alaskensis . Therefore, B. harveyi is a polyphagous parasite that concentrates on the most predominant host in its range. We conclude that no practical method of improving the effectiveness of B. harveyi on P. alaskensis currently exists.
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