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Spider predators of the spruce budworm Christoneura Fumiferana (Clem), at Lillooet, British Columbia Turnbull, Albert Lloyd

Abstract

In the region of Lillooet, B.C. a small population of spruce budworm, Ohoristoneura fumiferana (Clem.), has maintained a relatively constant sub-epidemic level for several decades, feeding on Douglas fir, Pseudotsuga taxifolia (Poir.) Britt. No tree mortality has occurred. This population has been under observation for ten years, and it is apparent that an effective natural control complex is operating in the area. Spiders are prominent among the predators of insects in the region. Field observations revealed that many spiders captured both larvae and moths of the spruce budworm. A collection of arboreal spiders of the region was made and identified. Feeding tests were conducted with spiders to determine the budworm-feeding species. Both caged and free spiders were tested. Population samples were taken to determine the relative abundance of spider species in the area, and to discover any differences that may exist between spider populations in the infested forest and in the non-infested forest. Four families were found to comprise eighty percent of the arboreal spiders of the Lillooet district, and seventy percent consisted of only two families, the Thomisidae and the Salticidae. The Thomisids do not capture spruce budworm larvae, but may capture moths. The Salticids capture both larvae and moths. Families Argiopidae and Theridiidae occasionally capture larvae and frequently capture moths. No difference was demonstrated between spider populations in the infested forest and the non-infested forest.

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