Return of the Pandora Moth

They’re back…! Just about the time we were beginning to forget them, ker-bango, the Pandora Moth has returned. If you don’t believe it, look at the walls of Sisters Rental and other buildings where lights in town are left on overnight. Moths are attracted to light.

The Pandora Moth, Coloradia pandora (Blake) is a phytophagous insect (feeding on plants, including shrubs and trees) that reproduces in impressive populations in eight- to 10-year cycles. “Impressive” means you cannot miss ’em!

The last outbreak of Pandoras began in the summer of 1989 throughout the Deschutes National Forest, and as far south as Klamath Falls. (For some strange reason, they are not found in Idaho or Washington).

By the summer of 1990, there were so many moth larvae (millions!) being squashed by vehicles on Highway 97 south of Bend that ODOT had to sand the roadway, and Golden Mantled ground squirrels, chipmunks, and birds thought they’d died and gone to heaven there were so many moths to eat.

Sunriver was almost in a blackout as store owners turned out lights to keep the adult moths from collecting on sidewalks and being crushed underfoot. For anyone who hasn’t lived in the pine-forested country of Central Oregon long enough to witness this natural phenomenon it can be quite a shock.

The first year the small black caterpillars are difficult to see, and try to keep out of harm’s way by feeding on the needles deep within a cluster. However, that doesn’t keep them safe from the tiny Braconid wasps, a parasite that attacks the moth larvae.

Braconid wasps (as well as tachinid flies) are effective agents that nature devised to feed on Pandora Moth populations. The more moths there are, the more wasps there will be; it’s the way the system works.

The Pandora, being a plant-eater, is confined to devouring the foliage of coniferous trees, mostly ponderosa pine in Central Oregon. They begin on last year’s foliage, but also eat the new foliage of this year’s growth. You would think, to look at a 90 foot Ponderosa completely defoliated by the moths, that they would die. However, Ponderosa Pine and Pandora Moths have been living together for many a moon and because of that both have adapted to not overdoing it.

Through some mysterious signal, moth larvae (caterpillars) stop eating before they kill the trees and begin the process of changing into adults. The larvae leave the tree and begin their journey to sandy soil that has just the right amount of consistency, moisture, and temperature for metamorphosis to take place.

The Pandora Moth requires two years to complete its life cycle. Adults appear the latter part of June and July, and the eggs hatch in August. The young larvae crawl up the trees and feed in groups on the new foliage, then immature larvae spend the first winter hibernating in clusters at the base of the needles.

Epidemics of the Pandora Moth are controlled by a number of natural factors. Perhaps the most important is a type of virus that affects the mature larvae. Once this disease becomes established it runs rampant and few of the insects survive. Direct control measures, such as chemical sprays, have not been devised specifically for the Pandora.

Most chemicals designed to deal with insect infestations kill parasites and smaller predators of the target species before they kill the so-called “pest.” In most cases, it’s best to let nature take her course.

However, being a moth caterpillar has other serious risks. Birds, such as jays, ravens and crows gobble them up, and the Flammulated Owl, Otus flammeolus, pigs out on both larvae and adults. In fact, Flammulated Owls eat just about nothing but insects as they travel from their wintering grounds in Panama to forests of Oregon and Washington where they raise their babies in summer.

In the Greek fable of Pandora’s Box, the lovely Pandora unleashed misery in the world, releasing “Hope” last.

We can rest easy knowing that Mother Nature has also supplied us with hope through natural controls for most of miserable pests that we must endure.