The Biology of the Mountain-ash Sawfly, Pristiphora geniculata (Htg.) (Hymenoptera: Tenthredinidae), in Eastern Canada

Abstract

The mountain-ash sawfly, Pristiphora geniculata (Htg.), a pest on Sorbus spp., is known to occur in Europe, Asia, and North America. It has two generations a year in eastern Canada but only one in northern Quebec. The first generation predominates. The sawfly overwinters as a larva in a cocoon in litter or soil. Adults emerge from late May to early July, and lay eggs in pockets between the epidermal lavers around the edges of leaflets. The eggs hatch in about a week and the larvae feed from two to three weeks. The second generation, which starts in late July, is usually small. Adults producing the first generation may come from both generations of the preceding year whereas adults producing the second generation stem only from the first. Parthenogenesis is facultative and arrhenotokous; about 61% of adults reared were females. The male larvae have four instars and the female five. Some larvae remain in diapause up to five years. Foliage consumption of female larvae was about 1.4 times that of male larvae.P. geniculata lacks adequate density-dependent control factors and an important limiting factor may be its scattered food supply. The introduction of parasites, predators, or disease organisms might be beneficial.