RECENT OUTBREAK OF THE LARCH SAWFLY, PRISTIPHORA-ERICHSONII (HARTIG), IN SUB-ARCTIC QUEBEC

Larch sawfly oviposition activity as revealed by scarring of long shoots of eastern larch, Larix laricina (DuRoi) K. Koch, was measured at various locations in the high boreal forest and forest tundra in Quebec in 1988 and 1989. The data show that larch sawfly is established up to the tree line, even on isolated larch growing under climatic conditions that are extreme for this tree. Frequency distributions of scarred shoots as a function of time suggest that larch sawfly populations reached outbreak levels in the 1980s, with peak numbers in 1981 for the high boreal, and in 1985 for the subarctic regions sampled. Trends in long shoot production by larch trees started to fluctuate simultaneously with the sudden increase in larch sawfly populations along the Grande Riviere de la Baleine in 1984. In this region in 1985, the proportion of long shoots used by Pristiphora erichsonii averaged 20-35%, which may have limited further population increase. Although foliage reduction and branch mortality were observed, mortality of whole trees was not a general characteristic of this outbreak.