Shades of Green: Earth's Forests -- Pests

Unfortunately, insects seem to have developed a reputation as being nothing more than disgusting and squishable annoyances. Insects are, however, vital to the survival of all forests. In abnormally large numbers, a few species can become "pests", but even these unusual occurrences can be part of a natural forest. Normally, there are enough predators to keep the pest populations within their limits.

In addition to the countless indirect ways in which insects are important to us, there are also more immediate benefits. Honey and wax are two very well-known products that come from insects. The honey and wax produced by domestic bees each year is worth hundreds of millions of dollars. The value of the crops that are pollinated by bees are worth 50 times this amount.

Bees are some of the most beneficial insects, but are killed by pesticides meant for other species. Photo by Maya Walters

This is not to say that insects don't harm trees. They do. Insects often kill trees. But do they harm the forest? Insect "pests" have evolved along with the forests and there is no such thing as a forest without a certain number of pest-ridden trees. Insects are just as much a part of the forest as the trees themselves.

In large numbers, grasshoppers can destroy crops that are planted in high densities of a single species, often on land that was once forest. Photo by Maya Walters

We tend to see insects that damage trees as pests because we look at the forest for its economic value. A dying tree with wood damaged by insects is worth little or nothing for timber, but it is worth a great deal to the forest. Woodpeckers drill holes in tree trunks to reach the insects inside; these holes become nesting sites for songbirds, which in turn feed heavily on other tree-damaging insects, keeping their populations low enough to prevent them from doing any serious damage to the forest.

The spruce budworm is one of the most destructive insects in northern coniferous forests (forests which are highly valued by people for their wood, which makes excellent pulp and paper products). The spruce budworm is actually not a worm, but a caterpillar, and mainly damages balsam fir, not spruce. The caterpillars feed on the leaves, buds, and twigs of trees, and a severely infested stand can become completely defoliated.

Severe outbreaks of insect pests, however, are rare, and occur much less frequently in natural forests than in "managed" ones. Most insects, including the spruce budworm, have their own natural enemies, which can usually keep their numbers low enough that they do not cause a problem.

Many insects hollow out tunnels in wood of dead trees to create nests -- the holes here were formed by carpenter ants, which live in the wood but do not eat it, as is commonly thought. Photo by Maya Walters

Insects can cause the most damage in planted "forests". In eastern Canada and the United States, the forests were once a diverse mixture of red spruce, Eastern hemlock, birches, pines, maples and other trees, in total over 20 species. Today, this forest is gone, and has been replaced by plantations of balsam fir and white spruce -- the two species preferred by the spruce budworm. These plantations are perfect habitat for this insect, which has reached epidemic populations. But the spruce budworm isn't the problem -- it existed in the ancient natural forests as well. The problem is the "monoculture", the huge single-species plantations, which allowed the insects to multiply to such huge numbers.

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