From Pine Beetles to Budworms: A Field Guide to Some of Canada's Worst Forest Offenders.
Insects are useful creatures indeed. Our lives have been enriched by their presence, and it is quite unlikely that we could survive on earth without them. They provide numerous products and services of great value. But a few insects can make us forget the beneficial nature of the vast majority.
Many of the tasty fruits and vegetables we rely on would disappear if it were not for pollinators of the six-legged kind. In some cultures, insects themselves are an item on the menu! And let's not forget honey, silk, and other useful products made by insects.
As to services, if it were not for the voracious appetite of some dung-feeding insects, the ground in some parts of the world would be covered in mounds of smelly animal droppings. Our knowledge of genetics and other areas of biology would not be as profound without the study of these invertebrates. In addition, insects, by the diversity of their behaviour, adaptations and colours, are fascinating in their own right.
Despite these benefits, there is a bad-bug minority whose damage can cost millions of dollars to the economy and wreak havoc on ecosystems. It is these bad bugs that tarnish the reputation of insects as a whole. Such is the case with some insects found in Canadian forests that are a thorn in the side of many foresters.
Here is a look at six species of insects that can leave a path of destruction in their wake. Some, like the Spruce Budworm, are native to Canada and are only truly harmful when their numbers grow out of balance. Others, like the Asian Longhorned Beetle, are non-native. Because they do not have natural predators to keep them in check, they multiply rapidly and seem to eat every tree in sight!
First, the native species:
Mountain Pine Beetle (Dendroctonus ponderosae)
Range: Western North America
Description: A stout reddish beetle 6 mm in length
Food: pine trees, especially lodgepole pine
Bad Bug Lore: Woodpeckers find this beetle's grubs tasty. The mountain pine beetle is very cold resistant, as it develops a kind of antifreeze in its body when the winter temperatures decline. The temperature has to persist at -40 C over several days in order to kill enough beetles to affect populations.
Bad Bug Damage: The tiny mountain pine beetle plays a natural role in the lifecycle of a forest. It tends to target trees that are weaker due to age, crowding, poor growing conditions, or other factors, thereby serving to recycle forests and contribute to natural succession. Trees killed by these beetles are an important component of the ecosystem, providing nesting, roosting, and feeding sites for many woodland birds. However, in British Columbia, unusually warm winters, forest fire suppression, and large, dense stands of mature lodgepole pine have allowed their numbers to explode to epidemic proportions. Under these conditions, the mountain pine beetle will attack a large proportion of the pine trees, healthy or not. The larvae kill pine trees by burrowing under the bark. Adult beetles kill trees by transmitting a fungus that grows through the wood. Healthy trees with good spacing are an effective deterrent to mountain pine beetles.
Forest Tent Caterpillar (Malacosoma distria)
Description: Adult is a yellow-brown, stout, hairy moth. Larvae are blue with red stripes and white dots, slender and hairy, 3 to 7 cm in length.
Food: Deciduous trees, with aspen and poplar being favourites.
Bad Bug Lore: An important food source for more than 60 species of birds, such as the northern oriole. Some bird populations, such as cuckoo, have been found to increase during years of tent caterpillar outbreaks. Although they are named tent caterpillars, these larvae do not actually spin a tent. Instead, they form a silken mat on the trunk or branch where they congregate when at rest or during moulting periods.
Bad Bug damage: Outbreaks occur in six to 16-year intervals and can last up to a maximum of five or six years. Forest tent caterpillars will almost completely exfoliate their host trees, although this seldom kills the tree. Repeated defoliation can lead to some dieback or reduced growth, which can be a concern for commercial tree plantations. In Canada, Btk, a natural pesticide is sometimes used to control outbreaks in plantations. Although Btk does not pose a threat to humans and other vertebrates, it does kill the caterpillars of beneficial butterflies and moths. It should be used only when absolutely necessary.
Spruce budworm (Choristoneura fumiferana)
Range: North America, east of the Rocky Mountains
Description: Adults are extremely variable, with colours ranging from dull grey to while. Wingspan 2.1-3 cm. Larvae are small, 1.9-2.4 cm long with black heads and dark brown body.
Food: Larvae feed on the new shoots of spruce and fir trees. May also feed on cones.
Bad Bug Lore: When feeding, the spruce budworm mines under the leaf bud caps and feeds on the expanding shoot within. Spruce budworms usually target trees that are old, and as such, play a role in forest regeneration. Evening grosbeaks love to eat spruce budworms, which are an important food source during outbreak years.
Bad Bug Damage: Outbreaks occur in 30-year cycles and can last 10-15 years. Spruce budworms are voracious defoliators. There is generally little impact from a single year of defoliation, but several consecutive years of needle-munching can make the trees more susceptible to disease and other insects. Chemical pesticides are seldom used to control the spruce budworm. Improved forestry practices or, if necessary, the use of pheromone traps, Btk, or experimental biocides are now the control methods of choice where economic losses are a concern.
Now, the alien forest offenders:
Gypsy Moth (Lymantria dispar)
Origins and range: Europe and Asia; now also found in Eastern North America
Description: In adults, the sexes differ. The females, which are white, are much larger than the males, with a wingspan of 5-7 cm. Males are brown, wingspan is 3-4 cm. Larvae are 5-7cm and charcoal grey in colour with a double row of five blue and six red dots on their backs. Small tufts of hair stick out of these dots.
Food: deciduous trees, especially oak
Bad Bug Lore: M. Leopold Trouvelot, who planned to raise the moth for silk production, deliberately introduced this bad bug to North America in the late 19 th century. Unfortunately, some of the moths escaped and have been causing damage ever since. Unlike their Asian counterparts, European gypsy moth females cannot fly. They emerge from their cocoon swollen with eggs, and release a pheromone that attracts the fully mobile males. The female only mates once and then lays all her eggs in one mass. Since females cannot fly, the species spreads in the caterpillar stage. Young larvae emerge from their eggs, climb to the top of a tree and hang from a branch by a silky thread. This allows the wind to pick them up and carry them to neighbouring trees.
Bad Bug Damage: In comparison to other types of forest pests, the gypsy moth is but a small-time offender. Nonetheless, it can cause short-term damage to trees by devouring all the leaves. Because broad-leaved trees are generally resilient, they usually survive such defoliating attacks. Gypsy moth caterpillars can indirectly harm wildlife by defoliating oaks. When this happens, the oaks conserve energy by ceasing the production of acorns, upon which many species of wildlife depend to survive the winter months.
Asian Longhorn Beetle (Anoplophora glabripennis)
Origins and range: China, Korea, Japan. In Canada it has been detected in the city of Vaughan, Ontario, where it is under eradication.
Description: The adults are large bluish-black beetles (2.5 to 3.5 cm in length) with white spots and very long antennae.
Food: The larvae feed on a variety of hardwood trees. In Asia the primary hosts are maple poplar and willow ( Salix).
Bad Bug Lore: In Asia, this beautiful yet destructive insect is also called the Starry Skied Beetle. There are several native beetles that are similar looking to the Asian Longhorn Beetle, such as the white-spotted sawyer beetle.
Bad Bug Damage: The Asian Longhorn Beetle, which has been introduced to our country by “hitch-hiking” on wooden packing material from other countries, is causing quite a stir. Even though it has not yet made its way into Canadian forests, the Canadian Food Inspection Agency (CFIA) has taken measures to control its spread. This is because it poses a significant threat to our deciduous forests. The larvae of this beetle kill hardwood trees by burrowing deep under the bark, weakening and killing the tree. The CFIA is currently implementing an aggressive eradication campaign.
Brown Spruce Longhorn Beetle ( Tetropium fuscum )
Origins and range:Northern Europe, Western Russia. In Canada, it has been found in Nova Scotia.
Description: 1-1.5 cm long. Brown or reddish-brown with two or three stripes that run lengthwise along the back. The body is flattened and the head is dark. It has long, reddish antennae.
Food: Larvae of this beetle feed on spruce trees by tunneling through the trunks.
Bad Bug Lore: In Europe, this beetle is relatively harmless, and usually feeds on sick and dying trees. Here in Canada, the beetle attacks healthy trees. Since there are no natural predators, their numbers are increasing at an alarming rate.
Bad Bug Damage: Like their Asian Longhorn counterparts, these destructive beetles have arrived by hitching a ride on wooden packing material. The Brown Spruce Longhorn Beetle arrived by ship, and its port of entry was Halifax, sometime in the late 1980s. It has since destroyed thousands of spruce trees in that city's parks. The city is considering taking a drastic step by destroying the nearly ten thousand spruce trees that have been affected by the beetle. Like the Asian Longhorned Beetle, the Brown Spruce Longhorn Beetle has the potential to destroy large tracts of forest in Canada.
Every bug plays a part
These so-called "bad" bugs have become problematic simply because their numbers are out of check, either because they are living outside their natural range or because of environmental factors. Under normal circumstances, these species can be beneficial to the forest because they play an important role in the ecosystem. For instance, native wood-boring beetles break down dead or dying trees. This allows fungus to enter and speed up decomposition. Also, the beetle larvae feed woodpeckers and other birds. In the forest, such processes have been going on for years, and they are as natural as birdsong or the gentle flow of a mountain stream.