Order:    Hymenoptera

Family:    Diprionidae

Latin Name:   Neodiprion abietis (Harr.)

Common Names:   Balsam Fir Sawfly

Introduction
Top

The presence of the balsam fir sawfly was recorded in North America in 1910. In Nova Scotia, recorded outbreaks date back to 1942. Outbreaks usually lasted three to four years with a varying number of years in between. There have also been high populations in Quebec, Ontario, and Newfoundland.

The principal host is balsam fir but it can also be found on white spruce, black spruce, and red spruce. Beginning infestation as usually occur in pre-commercial thinnings (PCT’s) of balsam fir stands before moving to unthinned areas.

Adult: resembles a small wasp, with four membranous wings; female brown, male black Lengths: 6-8 mm (female) and 4-5 mm (male).

Egg: Oval-shaped; white.

Larvae: Cylindrical, elongated; initially green, taking on a blackish colour as it matures. Length when mature: 20 mm.

Pupa: Enclosed in an oval cocoon; dimensions slightly larger than the adult (about the same size as a Rice Krispie).

Life History
Top

The balsam fir sawfly overwinters in the egg stage. The adult female cuts a small slit in the edge of the needle with her ovipositor and lays egg in the leaf cuticle. There is generally only one egg placed in each needle and they are usually laid in the current year’s growth.

When the buds open in the spring, the eggs hatch and the larvae feed in colonies of 30 - 100 larvae. They rarely feed on the new shoots but concentrate on the previous year’s growth. The larvae strip the outside of the needle, leaving a central filament that in time shrivels and finally takes on a brick red colour. The larva goes through 6 growth stages (instars) before they are mature and begin to pupate. This takes about one month.

Pupation occurs around mid-June. The pupae can be found on the ground or among the needles in the foliage. The adults hatch about a month after pupation, mate and lay eggs.

Records indicate that there is only one generation per year in Canada.

Damage Symptoms
Top

The damage done by the balsam fir sawfly larvae is threefold:

• feeding causes defoliation
• reduced growth
• tree mortality

The damage is only done by one life stage; the larva. The other stages do not cause direct damage to the tree.

Diagnosing the damage can be done in the winter months by examining the upper parts of the fir crown. By then, the branches are bare of all but the current year’s growth.

In the summer, look for the larvae feeding on the previous year’s growth.

Control Options
Top

These insects are attacked by various parasites and diseases. These will reduce the length of an outbreak but generally do not reduce the population before the damage and mortality occur.

A contact insecticide can be used to control a small population.

Research is ongoing to develop an useful and safe control option using a virus that affects the balsam fir sawfly.