The pesky Spruce Budworm

By Al Lowe
Contributor

We have all heard about this little insect, even if we don't know very much about it. It causes immense damage to the forests of Eastern North America. In Northern Ontario, where so much of our well-being depends on the evergreen trees, we should be very concerned about this little pest.
What does this insect do, to cause the immense damage we hear about so much? Actually, in spite of its name, this budworm prefers balsam fir as its favourite food, although it does heavily infest the spruce trees as well. The little caterpillar (the larvae) appear just as the buds on these trees are beginning to grow. These are the new needle buds, not the flowers. The caterpillars feed on these buds. If the infestation is heavy, then all the new growth for that year is eaten. And if that infestation persists for a few years, then the whole stand of trees dies, and the forest is useless for most practical purposes.
The Spruce Budworm, whose scientific name is Christomeura fumigerana, is a little brown moth in the adult stage. These are around in July and August - plain, brownish, mottled little insects which you wouldn't pay any attention to at all. They lay their eggs in masses on the fir and spruce trees. Eggs hatch in about ten days, into tiny caterpillars. These promptly spin little shelters for themselves in crevices in bark, and hibernate until the following spring. Then they emerge and begin to eat. They eat continuously during the warm parts of the days, for about five weeks. By then, they are about an inch long.
The larvae then form pupae, which are small motionless structures. Inside, however, the larvae are changing into the adult moths, a process which takes about 10 days to so. When the moths come out, the whole process starts all over again. Note that these insects are in hibernation for almost 10 months out of the year.
There are some natural controls on the Budworm. First, the birds. Birds such as warblers, chickadees, and nuthatches, to name a few, consume an enormous quantity of moths, eggs and larvae. But for birds alone to quell a heavy infestation would take several years. A sharp frost in the spring after the larvae have hatched, will reduce numbers dramatically. However, this is an 'iffy' probability, one which you can't count on. The Budworm is subject to quite a few diseases as well. But this too can't be counted on.
Control by man is almost always by spraying, chiefly with chemicals. New Brunswick has been spraying for nearly 50 years, a program which has generated violent controversy ever since it began. A few years ago, a new type of spray was developed, using a bacterium (called Bt) which affects the budworm caterpillar, but not too much else. It is not nearly as effective as some other forms of insecticide, but it apparently has no effect on birds, or other forms of life.
The controversy over spraying with chemicals will go on for a very long time, probably with no ultimate solution. Here in the north, we depend on the survival of the boreal forest. The outcome of the whole argument is of great concern to all of us.