Insect and Mammal Predation of Yellowheaded Spruce Sawfly Cocoons (Hymenoptera: Tenthredinidae) 1

Abstract

Predation by small mammals and insects on overwintering cocoons of the yellow headed spruce sawfly, Pikonema alaskensis (Rohwer), was measured using an exclusion cage technique. In exposed soil cores mammals preyed on a total of 45.2% of the “planted” cocoons and insects preyed on an additional 20.3%. Insects preyed on 38.8% of the cocoons in cores enclosed by mammal exclusion cages. Eight species of small mammals were trapped in the study areas. Elaterid and carabid larvae were the dominant insect predators. In the soil cores 95.2% of the sawfly cocoons were at a depth of 2 cm or less. Mammal and insect predation rate was slightly heavier on cocoons in the surface stratum than on cocoons deeper in the soil.