With summer winding down and temperatures starting to cool off, many residents of North Central West Virginia look forward to Mother Nature's awesome display of natural fireworks as the region's varieties of deciduous trees shed their multi-hued leaves.
For Lewis and Upshur counties, however, that transformation will be muted this year as many of the region's oak trees have been infested with a destructive insect that causes leaves to prematurely turn brown.
"It's not really a danger to the trees, it's more of an ugly at this point," said Sherri Hutchinson, forest entomologist for the state Department of Agriculture's Plant Industries Division. "We get these nuisance-type outbreaks because the populations get real high. Through a natural cycle of predators, the populations will crash, but it gets very ugly, with the trees turning brown like that."
The culprit is the scarlet oak sawfly, also known as a slug sawfly. The insect, which resembles a small housefly, emerges in the spring and the females lay eggs in fully-grown oak leaves. When the caterpillar-like larvae hatch, they feed on the underside of leaves, she said. Several larvae, which are yellow-green and look slimy, share the same leaf and feed on the leaf tissue, leaving a fine network of veins that give the leaf a transparent, lacy look.
The feeding insects also cause the leaves to turn brown, she said.
"They start high on the tree at the beginning of summer and the trees get a brown top," she said. "As it gets later in the season, the brown leaves can go all the way to the bottom, depending on the extent of the infestation."
In 1997 and 1998, the sawfly infested between 115,000 and 185,000 acres of forest in Wayne, Cabell, Mason and Putnam counties. This summer, sawfly defoliation was clearly evident in about 18,000 acres of forest in Lewis and Upshur counties.
"Before that, there were really no bad outbreaks since the late 1960s or early 1970s," she said. "Because they are native pests, when the natural bacteria and other predators are not evident, the sawfly populations go up."
Fully grown larvae are 1/2-inch long, she said. After molting for the last time, the sawflies lose their coat of slime and fall from the leaves where they pupate in the loose soil around the tree base. There can be up to three generations per summer, which explains the gradual defoliation, Hutchinson said.
"From a foresting situation, there's really nothing that can be done," she said. "For yard trees, people can use Sevin or another contact insecticide to kill the sawflies."
Regional writer James Fisher can be reached at 626-1446 or by e-mail at firstname.lastname@example.org