2017-11-25

Balsam Fir Sawfly (BFS)

Photo Credit: Natural Resources Canada

The balsam fir sawfly (Neodiprion abietis) is a native insect that feeds on the needles of balsam fir, black spruce, red spruce and white spruce and was recorded in North America in 1910, with Nova Scotia recording outbreaks as early as 1942 and high populations have been recorded in Quebec, Ontario and Newfoundland.

When feeding the larvae strip the outside of the needle, leaving the central filament that in time shrivels and finally takes on an orange colour. They rarely feed on the previous year's growth. After 3-4 years of infestation, trees will exhibit significant growth loss and become weakened, therefore making them vulnerable to attack by other organisms. The pre-commercial thinning of a balsam fir stand usually serves as the entryway for an infestation.

The adult resembles a small wasp, with four membranous wings, females are brown (6-8 mm), males are black (4-5 mm). Females lay white, oval-shaped eggs and the green cylindrical larvae take on a blackish colour as they mature. The cocoon of the pupa is about the size of a rice-style cereal grain.

 The adult females lay the eggs in the current year’s growth but cutting a small slit in the needle with her ovipositor in the leaf cuticle and the balsam fir sawfly overwinters in this stage. In the next spring, when the buds open, the eggs hatch and the larvae feed in colonies of 30 - 100 larvae.

PHOTO CREDIT: NATURAL RESOURCES CANADA

 In mid-June the insect pupate and they can be found on the ground or among the needles in the foliage. After about a  month of pupation the adults, mate and lay eggs. Records indicate that there is only one generation per year in Canada.

Further Web Resources

CFS Balsam Fir Sawfly FAQs

Information was provided by NRCan and partially excerpted from NS DNR.

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