JoAnne Skelly: Invasive moth species hazardous to trees

I’m finding pretty white moths sitting on our patio. They are about one-inch long with black and white striped legs and a black spot on their heads.

I wondered if I was seeing the invasive white satin moth, Leucoma salicis. After I sent pictures to Wendy Hanson Mazet, horticulturist at University of Nevada Cooperative Extension, she confirmed it was the invasive pest.

White satin moths are relatives of the infamous gypsy moths. In 2017, Nevada Division of Forestry officials said the moth was responsible for 40-70 percent canopy loss in forests at Lake Tahoe Nevada State Park.

The caterpillars eat and skeletonize the leaves of aspen, poplar, willow, and sometimes oak trees, leaving only the veins. If trees are defoliated year after year, they can die.

The silvery-white moths are satiny in appearance, but their bodies are actually black but covered with a dense jacket of white scales and hairs.

Their wingspan is 1 1/2 to 2 inches. The caterpillars, or larval stage of the moths, are almost 2 inches long and range from a pale grayish-brown to black. They have shiny milk-white or yellowish spots along their backs with tufts of reddish brown hairs on the back and sides. Pupae are dark-brown to black, shiny and hairy in a loose cocoon, often inside rolled leaves. The eggs are greenish and flat-round, laid in groups and covered with white froth (University of Wyoming Extension).

After hatching from eggs in August, the caterpillars feed into September before settling in for winter in a web camouflaged to look like bark. After overwintering, they eat again in the early summer of the following year before turning into pupae.

Adult moths emerge from pupae in late June to mid-August, becoming most numerous around mid-July. Females lay eggs on twigs or tree branches starting in July.

Birds, predatory and parasitic insects such as lacewings, wasps and flies attack the larvae. However, sometimes populations soar and trees suffer.

Bio-insecticides containing the bacteria Bacillus thuringiensis var. kustaki are effective management strategies if applied when caterpillars are young.

Homeowners can also use a high pressure hose on affected trees to knock the larvae and eggs loose. Sticky bands applied to the trunk can trap the caterpillars as they climb the tree to feed.

Or, when you find moths, larvae or eggs, put them in a plastic bag and squish them!

For information, go to http://forestry.nv.gov/wp-content/uploads/2012/07/white-satin-moth.pdf.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.