SASKATCHEWAN — Saskatchewan arborists are hoping to find a way to fight back, as they try to reclaim their beloved trees from the increasing number of tent caterpillar webs across the community.
According to research with the College of Agriculture and Bioresources at the University of Saskatchewan, tent caterpillar populations tend to explode every eight to 10 years, often lasting between two and three years. While the damage caused by the fuzzy beings may look worse than it really is, most trees do recover from the defoliation caused by their attackers. There are three common types of tent caterpillars found in the region: forest tent caterpillars, eastern tent caterpillars and western tent caterpillars.
Life cycle of tent caterpillars
The life of a tent caterpillar starts in mid-summer, when mature larvae emerge from their pupae and begin to mate. Female moths can lay between 150 and 250 eggs, usually in the higher crowns of deciduous trees, in a band around the limbs of trees. The embryos develop into larvae before the temperatures drop but will not emerge until late April to early May. When the eggs hatch, the larvae begin feeding on the new foliage surrounding them. The feeding frenzy continues until the larvae are fully grown, near mid to late June, when they pupate for two weeks before they transform into moths.
While the three species have very similar life cycles, the eastern and western species often build tent-like webs between tree branches for the larvae to pupate in, rather than the silken mats the forest tent caterpillars create on trunks or branches for the duration of pupation. Another difference is that the western tent caterpillar moth appears later in the summer, laying eggs throughout August.
Signs of tent caterpillar infestation
It is not always easy to know if you will have an infestation of tent caterpillars until the following summer. The egg bands are made of a frothy substance that hardens into a shiny, Styrofoam-like material. Once the caterpillars have hatched from the band, they start to create their webbed tents, which increase in size as the larvae grow throughout the feeding period. During severe outbreaks, millions of larvae can starve if the local food supply has been completely consumed before reaching maturity.
The winter and spring weather can also have a huge impact on tent caterpillar populations each year. Cold springs or severe late-spring frosts delay leaf-out on host trees and can even kill the larvae directly. Egg mortality can also be affected by extreme cold winter temperatures in more northern climates.
Another natural factor that can regulate the population of tent caterpillars is parasitoids, natural predators and diseases. The large flesh fly targets caterpillar pupae and can destroy up to 80 per cent of the population in a season. Birds that eat both larvae and moths are also key in reducing caterpillar numbers, as are diseases such as microsporidia, fungi, nuclear polyhedrosis virus (NPV) or cytoplasmic polyhedrosis virus (CPV).
How to control an outbreak
There are a few options to help reduce tent caterpillar populations from year to year. In the fall, early winter or early spring, egg bands can be discarded after gently scraping them away or cutting the twigs they are on.
During the summer months, the cocoons, which are usually found on tree trunks, fences, debris and sheltered areas, can also be scraped off gently and discarded.
If the large tent webbing has already been formed, wait until early morning or late evening to remove the webs. Many of the caterpillar population will be within that webbing during those times of the day.
Using plain water can also help reduce the population in your yard. Knocking the fuzzy pests from the tree with water may be enough to kill them, as they drown easily. However, this practice does not always stop survivors from crawling back up and continuing to damage foliage.
One of the favoured methods of controlling tent caterpillars is Bacillus thuringiensis, most commonly known as Bt. Bt is a bacterium that can be sprayed on the leaves of the host tree, killing the caterpillar after ingestion. While its effectiveness has been proven, it also reduces the already declining numbers of other larval species, such as other moths and butterflies.
What if there is already damage?
Tent caterpillars can wreak havoc on the trees they call home, stripping branches of their leaves. While the caterpillars prefer aspens, they will also feed on oak, basswood, ash, poplar, cherry, plum, raspberry and apple trees.
To help trees recover from defoliation, providing an inch of water on a weekly basis will help keep them healthy. It is also wise not to fertilize when caterpillars are still feeding, as it may add stress to the tree.
