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Balsam fir sawfly
Thérèse Arcand
New fir shoot, showing many needles bearing egg-slits
Thérèse Arcand
Close-up of egg outside of egg-slit
Thérèse Arcand
Mature larva on fir twig (length: 20 mm)
Thérèse Arcand
Female and male adults near their respective cocoons (length: 6-8 mm and 4-5 mm, respectively)
Thérèse Arcand
Fir twig defoliated: 1) current year's foliage is intact; 2) 1-year-old needles are chewed and reddened; and 3) 2-year-old needles have disappeared
René Martineau
Close-up of a reddened fir crown following an outbreak
Latin name: Neodiprion abietis (Harris)
English name:
Balsam fir sawfly
French name:
Diprion du sapin
Order:
Hymenoptera
Family:
Diprionidae
Main host(s)
Balsam fir, black spruce, white spruce
Phyllophagous
- Free-living defoliator
Micro-habitat(s)
Needle
Distribution
Canada
Damage, symptoms and biology
The first sign of the presence of the balsam fir sawfly is the reddening of the needles in the interior of the crown in July on twigs that are one year old and older. In winter, the presence of the insect is recognized by the partial defoliation of the upper part of crowns, which current-year shoots are still green. The eggs deposited on the needles of unaffected current-year shoots are then visible. Balsam fir sawflies overwinter as eggs and the larvae emerge from the eggs when the buds open in the spring.
The larvae live in colonies and feed on the needles, causing them to turn brown. Immature larvae eat only parts of the needle, while mature larvae will consume the entire needle, except for the central part. The affected needles shrivel, dry out and drop off.
After several years of infestation, significant growth loss will occur in affected species and the trees become weakened, making them susceptible to attack by other organisms. Balsam fir sawflies seldom cause tree mortality, even during severe and prolonged infestations.
Life Cycle (East of the Rockies)
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Balsam fir sawfly is a native species and is widespread in Canada. Outbreaks generally occur in conjunction with three other insects: spruce budworm, eastern blackheaded budworm and balsam woolly adelgid. The insect was first reported in Canada in 1936. Outbreaks of varying intensity and duration occur every year, depending on the province. In Quebec, it attacks primarily average-age stands dominated by balsam fir and where density is moderate to low.
Control measures are not recommended due to the effectiveness of natural factors, including a virus that has largely contributed to maintaining populations at low levels. However, when crowns are invaded by feeding larvae, they can be made to drop to the ground by striking the trunks with an instrument.