COMPETITION AND CO-OPERATION BETWEEN CHRYSOCHARIS LARICINELLAE AND AGATHIS PUMILA ON LARCH CASEBEARER IN QUEBEC

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Abstract
Agathis pumila (Ratzeburg) and Chrysocharis laricinellae (Ratzeburg) compete for their common host, the larch casebearer (Coleophora laricella (Hübner)). An analysis of the mechanism of this competition, based on a 2-year study at Joliette, Que., is presented. A. pumila, in sacrificing part of its own population, prevents a "one stage condition" and helps C. laricinellae build up to a point where the latter becomes host-regulative by massive attack. Competitive displacement of A. pumila by C. laricinellae is less frequent than expected because of the basically different ways in which the two parasite species spread, search for, select, and attack hosts. A. pumila may suffer about 50% loss from multiple parasitism, but apparently this does not affect its survival potential, its reproductive rate, and its ability to provide significant partial control of the larch casebearer.