OVIPOSITION, TEMPORAL DISTRIBUTION, AND POTENTIAL IMPACT OF STROBILOMYIA LARICIS MICHELSEN AND S. VIARIA (HUCKETT) (DIPTERA: ANTHOMYIIDAE) ON EASTERN LARCH, LARIX LARICINA (DU ROI) K. KOCH

Abstract

AbstractA 2-year field study was carried out to locate and identify eggs, determine the temporal distributions of eggs and larvae, and assess the impact of Strobilomyia laricis and S. viaria on Larix laricina. Eggs of S. laricis were beige with a patterned surface and usually laid one per cone in the bud scales at the base of the cone. Eggs of S. viaria were white and smooth and usually laid one per cone between the ovuliferous scales of the cone. Strobilomyia laricis oviposited from mid- to late May and S. viaria from late May to mid-June, each species initiating oviposition at a different stage of cone phenology. Peak egg densities of S. laricis were 25 and 65% higher than those of S. viaria in 1990 and 1991, respectively. Larvae of both species completed development at the same time, from mid-June to early July. The mean number of scales eaten per cone did not differ between species; one larva damaged a mean of 8.4 scales per cone in 1990 and 10.7 scales per cone in 1991. As the number of scales per cone increased, the mean number of scales eaten increased and the mean percentage of scales eaten decreased. Cone crops were light in both years. In 1990, the only year we were able to differentiate cone maggot larvae, 44% of cones were damaged by S. laricis and only 16% by S. viaria. Together, S. laricis and S. viaria damaged 60 and 67% of the cones and destroyed 38 and 50% of the potential seed crop in 1990 and 1991, respectively.