EVIDENCE FOR MORTALITY IN ADDITION TO SUCCESSFUL PARASITISM OF NEEDLEMINING LARCH CASEBEARER (LEPIDOPTERA: COLEOPHORIDAE) LARVAE BY AGATHIS PUMILA (RATZ.) (HYMENOPTERA: BRACONIDAE)

In an attempt to control the larch casebearer, Coleophora laricella (Hübner), in western North America with biological agents, insect parasites from Europe and Japan were introduced (Denton 1972, 1979; Ryan et al. 1987). The braconid Agathis pumila (Ratz.) has become widely established and apparently has been responsible for markedly reduced casebearer densities (Ryan 1983, 1986; Ryan et al. 1987). Parasitization by it in many research plots reached 80-95% (unpublished data), then declined following reductions in the casebearer populations in a typically delayed density-dependent manner. I present here a partial explanation for why casebearer densities declined so drastically, to levels even lower than could perhaps be explained by parasitization at such high levels.