FOREST HEALTH: Jack Pine Budworm in Ontario
by Mike Francis

Jack pine budworm is the most serious insect affecting jack pine in Ontario. This insect looks similar to the spruce budworm, a close relative which attacks balsam fir and spruces. The jack pine budworm is a solitary feeder native to North America and can be found across Canada coinciding with its preferred host, jack pine. This defoliator prefers jack pine but can also be found on red pine, Scots pine, eastern white pine, and occasionally on fir, spruce, and larch when they are minor components of large jack pine stands. 
Two to three consecutive years of severe defoliation by heavily infested areas of jack pine budworm can cause top mortality and some whole tree mortality in jack pine stands. A reduction in tree growth also occurs during and after an infestation of this defoliator. These impacts can affect wood supply, wildlife habitat, and aesthetics as well as increase conditions that are suitable for high intensity fires.

The life-cycle of the jack pine budworm closely resembles that of the spruce budworm but development occurs approximately two weeks later. Small overwintering second instar larvae emerge from under the bark in late May or early June and begin feeding on the pollen in male flowers or on developing needles of new shoots. The abundance of male flowers determines early survival of the larvae in the spring. The full-grown larva transforms into pupa case on the shoot and in July and early August the adult moth emerges, mates and the female deposits her eggs on the host tree’s needles. These eggs are laid in clusters of two overlapping rows, with approximately 40 eggs per cluster. Within 10 days the eggs hatch and the tiny larvae find protected areas under the bark and spin up a silken shelter where they moult to the second instar and spend the winter.

In Ontario, outbreaks of jack pine budworm occur about every 8-10 years, and typically last 2-4 years in any one location (Figure 1). The most recent outbreak in Ontario began in 2004 when 851 ha of moderate to severe defoliation was aerially mapped in the Sudbury District of the Northeast Region (Table 1), and during regular forest health surveys egg masses were recorded in the Fort Frances District of the Northwest Region. 

In 2005 the infestation dramatically increased in the Northwest Region to 88,445 ha of damage, and also increased in the Northeast Region to 3,552 ha. A small area of moderate to severe defoliation (222 ha) was also seen in the Pembroke District in the Southern Region.

In 2006 areas of defoliation were mapped in the Northwest Region reaching a total of 720,172 ha of moderate to severe defoliation. An increase was also mapped in the Northeast Region. The Southern Region experienced new defoliation in the Parry Sound District with a small increase in the Pembroke District.

The jack pine budworm defoliation in 2005 in the Northwest Region prompted an insect pest management program in 2006. The program was developed by an interdisciplinary team comprised of MNR district, regional and Forest Management Branch staff, staff of the sustainable forest licensees, and representatives of the local citizens’ committee. In accordance with the Forest Management Planning Manual for Ontario’s Crown Forests a range of management options were considered including no treatment, accelerated harvest, redirected harvest, salvage harvest, the use of insecticides, other controls, and a combination of no treatment and other controls. Overall, based on the evaluation of the management options, the planning team decided that aerial spray with Bacillus thuringiensis var. kurstaki (Btk) combined with re-directed harvest and no treatment was the most acceptable way to ensure that tree growing investments are protected with the least impact to the environment. 

The purpose of the spray program was to protect the trees through the outbreak, mitigating wood and wildlife habitat losses as well as diminishing the fire hazard.

A total of 14 spray planes were used to spray 109,131 ha of infested jack pine stands in the Fort Frances, Kenora and Dryden districts in June 2006. Protection and spray deposit was very good in the blocks assessed. Defoliation in sprayed areas averaged 37%, while the control areas had an average of 72% defoliation. 

Mike Francis is Provincial Forest Health Technician with the Ontario Ministry of Natural Resources - Forest Health and Silviculture Section. He can be reached at 705-945-6763.