Balsam shootboring sawfly

View from above of the larva on damaged annual shoot Thérèse Arcand

French common name: Perce-pousse du sapin
Scientific name: Pleroneura brunneicornis Rohwer
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Xyelidae
Partial list of synonyms:
- Pleroneura borealis Felt

Distribution

Canada

Damage, symptoms and biology

Wilting current-year shoots with a reddish brown appearance are characteristic of attacks by balsam shootboring sawflies. The damage, which is visible in late June, is similar to that caused by late frost. During summer, the weakened current-year shoots drop to the ground in bad weather. Even when present in large numbers, the balsam shootboring sawfly does not cause tree mortality.

In May, the female lays an egg at the base of terminal buds. Upon hatching, the larvae bore a tunnel into the new shoots. When mature, the larvae drop to the ground and spin cocoons, in which they overwinter. It is believed that part of the population remains in the soil in diapause for an entire year.

Other information

Native to North America, the balsam shootboring sawfly occurs in Canada, primarily from Nova Scotia to Alberta, and in the northeastern United States.

The insect generally prefers young firs under two metres in height and growing in open areas or in Christmas tree plantations. Balsam shootboring sawfly infestations are of short duration.

If ornamental or Christmas trees are heavily damaged, it is recommended that the annual shoots be pruned to improve the appearance of the trees. Control measures are not currently used in Christmas tree plantations against this insect.