none Between 1973 and 1983 two newly introduced parasites, Agathis pumila (Ratz.) and Chrysocharis laricinellae (Ratz), caused an increasing impact on populations of the larch casebearer, Coleophora laricella (Hbn.), as measured by percentage parasitism based on adult emergence and the associated mortality of hosts that did not produce parasites. Trends in parasite effectiveness are represented by percentages based solely on adult emergence. Only 53.1% of the adult A. pumila successfully emerged in 1983 samples. Furthermore, the number of emerged plus non-emerged A. pumila was only 53.3% of the number expected based on previous samples of that same generation. This mortality of A. pumila took place even in the absence of significant populations of C. laricinellae , indicating that although C. laricinellae may cause some reduction in parasitism by A. pumila , other factors are also responsible.