Western
Tent Caterpillar Update
Biological Control: At this time of the year (June-July), the damage is done. Tent caterpillars are now digesting and looking for places to pupate. So put away the pesticides and enjoy the goriest horror show that nature has to offer. This is a great time to go out and look at nature’s arsenal for tent caterpillars. With high populations of caterpillars that are easy to find, you may witness nature’s most obvious killers of tent caterpillars: parasitoid flies and disease. Parasitic flies, in the family Tachinidae, are sneaking up behind unwary caterpillars and slapping them in the back of the head with one of their kids! Pictured is a great photo from Washington State Department of Agriculture chief entomologist, Eric LaGasa, showing the white egg of a tachinid fly located just behind the head of the tent caterpillar. Soon, this egg will hatch and a maggot will crawl out to gain entrance inside the caterpillar. Once inside the caterpillar, the maggot will graze on the not-so-vital organs like reproductive organs and fat bodies. Tachinid flies, such as in the genus Gonia, will continue to devour their host when the caterpillar has decided to pupate. Often you will find the devoured or almost-dead pupae and the pleasantly plump tachinid fly pupae in the same cocoon of the tent caterpillar. |
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Tent caterpillar diseases include virus, bacteria and fungi. The most common disease to flourish during a tent caterpillar outbreak is the virus. Pictured is the oozing mess left by a very sick caterpillar. Multiple virus species attack forest tent caterpillars. Viruses tend to lay dormant in tent caterpillars until population outbreaks occur. On normal years, you can sporadically see sick caterpillars. During outbreak years, caterpillars become overcrowded, stressed and the virus will take advantage and proliferate. Generally, caterpillars become listless when sickened and will cease feeding. Often the caterpillar will migrate up the tree out to the tip of an overhanging limb. The caterpillar becomes consumed with virus and begins to ooze. The drippings from the oozing caterpillars land on the foliage beneath. This ooze contains more virus and waits for the next caterpillar to come by and feed on the contaminated foliage. |
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 Virus infected tent caterpillar larvae. |
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Natural control of tent caterpillar outbreaks can take a couple of years. Natural enemies (wasps, flies and disease) will continue to build large populations this year and next, soon bringing tent caterpillars under control again. This phenomenon, in conjunction to climate, reinforces the cyclical nature of tent caterpillars. In the mean time, continue squishing stomping and pinching them as the come. You too are a natural enemy of tent caterpillars!
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