Life Tables of the Yellowheaded Spruce Sawfly, Pikonema alaskensis (Rohwer) (Hymenoptera: Tenthredinidae) in Minnesota 1

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Abstract
From 1973–75, life tables of the yellowheaded spruce sawfly, Pikonema alaskensis (Rohwer), were constructed for use in selecting appropriate life stages for release of biological control agents. Plots were established in white spruce, Picea glauca (Moench) Voss, plantations near Grand Rapids, Minnesota. Sampling techniques utilizing the individual tree as the sampling unit are discussed. Six sections of the life tables are reported on as follows: (1) Overwintering predation by insects and small mammals killed 66.43% of sawfly cocoons in the soil. (2) 7 species of small mammals were present in the spruce plantation habitat and the predominant species changed from Microtus to Sorex and Blarina after sawfly larvae drop from the trees. (3) Field observations of insect, spider, and bird predators are presented. (4) Parasitism of the late instars ranged from 1.49–19.64%. No egg parasites were collected. (5) Life tables for the 1975 generation are given with a discussion of the different survival rates according to level in the tree. (6) Results show that the egg and early larval stages are the most appropriate points in the life cycle for release of biological control agents.

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