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How to identify it
- Wilting current-year shoots with a reddish-brown look, visible in late June, are the characteristic sign. The new shoot tips appear flattened, with the center turning red and dying.[1][2]
- The larva inside the shoot is yellowish white and about 6 mm long when mature. The adult resembles a small wasp, 5 to 6 mm long, with black and white stripes on the abdomen, and flies in early to mid spring.[2]
- The damage looks like late frost injury, so check for a tunnel in the wilted shoot. During summer the weakened shoots drop to the ground in bad weather.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Balsam twig aphid | Another insect of new balsam fir growth. The shootboring sawfly leaves a tunneled, wilted, reddish shoot tip with a yellowish-white larva inside, and the shoot later drops.[1][2] |
| Balsam gall midge | Another balsam fir Christmas tree pest. The shootboring sawfly kills the whole new shoot tip, which flattens, reddens and may drop in bad weather.[1][2] |
| Balsam woolly adelgid | The shootboring sawfly's damage is confined to the current year's shoots on young firs and lasts one season; it does not kill trees.[1] |
Where it lives
Native to North America; occurs in Canada primarily from Nova Scotia to Alberta, and in the northeastern United States. The iNaturalist taxon page spells the species name Pleroneura bruneicornis.[1]
Biology and life cycle
The host is balsam fir, and the insect prefers young trees under two meters tall growing in the open or in Christmas tree plantations.[1]
Adults fly in early to mid spring. In May the female lays an egg at the base of a terminal bud, and the hatched larva bores a tunnel into the new shoot, feeding from mid spring to early summer.[1][2]
Mature larvae drop to the ground and spin cocoons in which they overwinter, pupating the following spring; part of the population is thought to stay in the soil in diapause for a whole extra year. Infestations are of short duration.[1][2]
Damage and signs
Health risk
Neither source mentions any effect on people or pets; the adult resembles a small wasp and the larva lives inside fir shoots.[2][1]
Control
Prevention
Control measures are not currently used against this insect in Christmas tree plantations; infestations are short-lived and the trees are not harmed in the long run.[1][2]
Traps and physical control
If ornamental or Christmas trees are heavily damaged, prune off the affected annual shoots to improve the trees' appearance.[1]
Pesticides
Nova Scotia's guide notes that registered insecticides, applied according to label instructions, target the flying adults in spring; check what is currently registered with extension or the provincial or state forestry agency.[2]
Common questions
- The new tips on my young balsam firs wilted and turned red in June. Was it frost?
- Possibly, but the balsam shootboring sawfly causes the same look. Split a wilted shoot: a tunnel, or a small yellowish-white larva inside, means sawfly. The shoots often drop off later in summer.[1][2]
- Will it kill my Christmas trees?
- No. Even large numbers do not cause tree mortality, the damage is cosmetic, and infestations do not last. Prune the damaged shoots to tidy the trees.[1][2]
- Is there a spray?
- Christmas tree growers do not currently treat for it. Where a spray is used, it is aimed at the flying adults in early to mid spring, before eggs are laid at the bud bases in May.[1][2]
Sources
- Natural Resources Canada, Canadian Forest Service, “Balsam shootboring sawfly, Trees, insects, mites, and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/8030 (accessed 2026-11-10)
- Nova Scotia Department of Natural Resources, “A Field Guide to Pests of the Acadian Forest (Report FOR 2017-14), balsam shootboring sawfly entry.” novascotia.ca/natr/woodlot/pdf/Woodlot-Field-Guide-to-Pests-of-the-Acadian-Forest.pdf (accessed 2026-11-10)
- iNaturalist, “Pleroneura brunneicornis taxon page (order and family).” www.inaturalist.org/taxa/548344 (accessed 2026-11-10)