Balsam fir sawfly
Canada, United States
Damage, symptoms and biology
Balsam fir sawfly eggs are laid in slits cut by adult, female balsam fir sawflies in the current-year foliage of balsam fir trees in late August and September. The eggs overwinter there and hatch in June and July. Initially, larvae feed in groups on foliage that is one-year-old and older. As the larvae age, they feed on the older foliage throughout the tree.
Trees affected by the balsam fir sawfly characteristically have green branch tips and red-coloured needles towards the interior of the tree. Normally, balsam fir sawfly defoliation does not cause tree death, but it can significantly reduce tree growth and, therefore, productivity.
Life cycle (East of the Rockies)
The balsam fir sawfly is native to Canada where it can be found across the country. Balsam fir sawfly larvae feed on fir and spruce, although in different regions, they feed predominantly on a single host plant. For example, in eastern Canada, they feed mostly on balsam fir.
Normally, balsam fir sawfly populations are regulated by natural pathogens, parasites, and predators and outbreaks are short in duration. However, when outbreaks cause severe defoliation to valuable balsam fir stands, the biological control product Abietiv™ has proven effective in reducing balsam fir sawfly populations. Abietiv™ was developed and registered as a commercial product by the Canadian Forest Service of Natural Resources Canada.
Abietiv™ is a microbial pesticide which uses a naturally occurring virus in the balsam fir sawfly population to accelerate the natural collapse of the outbreak, thereby minimizing tree damage. Once eaten by a larva, the virus infects the cells of the insect’s gut. Infected cells, containing the virus, are excreted by balsam fir sawfly larvae before they die and when dead larvae decompose. As a result, the virus contaminates more balsam fir needles which are then eaten by other balsam fir sawfly larvae. In this way, the virus is spread through the balsam fir sawfly population.
Canadian Forest Service Publications
Diet and feeding behaviour
: Feeds on the leaves of plants.
- Free-living defoliator: Feeds on and moves about freely on foliage.
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