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Tree-eating insects munching their way across Interior

Posted: Tuesday, July 15, 2003

FAIRBANKS (AP) The mild winter and a population boom has resulted in a smorgasbord for insects that are munching their way across Alaska's Interior.

Call it the attack of the five-millimeter larvae. The birch leaf miner, birch leaf roller, aspen leaf miner and spruce budworm munched through Interior tree canopies from May through early June.

The insects are defoliators, or leaf-eating insects, and they are enjoying a veritable-all-you-can-eat buffet high in the trees.

''You've kind of got a double-whammy of higher insect survival and trees less able to provide defense,'' said Bob Wheeler, a forestry specialist with the Alaska Cooperative Extension.

Milder winters and warmer summers can create problems for trees' water supply, Wheeler said.

''With warming conditions, drought stress becomes more of a concern,'' he said.

Adult leaf miners, or sawflies are about three millimeters long and emerge from their subterranean winter cocoons in early May. They cut tiny slits on the surface of young birch or aspen leaves and lay their eggs inside.

Flat enough to live inside the leaf, the larvae ''mine'' green chlorophyll from the plant cells. With the chlorophyll gone, the leaf not only loses its component for photosynthesis, the conversion of light into usable energy, but its healthy green coloring.

When the insects leave in late June, the dying leaf is rife with colorless track marks. Fattened from their monthlong feast, the larvae drop to the ground in mid-June and spin protective cocoons.

Wintering as eggs on the bud stalks of birch trees, leaf rollers hatch in early May. As the tiny caterpillars feed on the infant buds and young leaves, they begin to roll the leaves into cocoons to wait out the next stage in their maturity.

As June turns to July, the mature caterpillars fall to the soil below and begin to pupate. By August, they emerge as small gray moths and flutter back into the trees to plant the next generation.

Spruce budworm larvae find a cozy notch or crevice in spruce foliage for the winter, spinning a cocoon against the cold. They emerge in mid-May and plunge into the lush infant buds of the spruce tree.

''It looks like someone took a lawnmower to it,'' Wheeler said, describing the budworm damage to spruce needles.

Budworms pupate among the spruce foliage until late June and soon emerge as adult moths, roughly a half inch long. They lay their green eggs in clusters of spruce needles.

After nearly 100 spruces on her three-acre lot were stricken with shriveled, worm-like needles, Rosie Creek resident Melody Springer contacted Wheeler for advice. It was indeed a budworm infestation, he concluded.

''The good news is that they (the trees) generally come back from this,'' Springer said, ''but the bad news is this cycle can go on for years. It's not so pretty to see all those brown tips on the spruce trees, but hopefully they'll stay healthy.''

Insecticides will do no good this season, as most of the bugs are already out of the trees and into the ground growing toward adulthood. The best times to combat the tiny leaf munchers are in May and June.

Wheeler doesn't think there's cause for concern over the defoliator epidemic just yet.

''You shouldn't think of this as being an extreme level of damage, because it can get a lot worse,'' he said.



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