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Caterpillar invasion sparks wildfire worries for Plumas residents

Laura Beaton
Staff Writer

Some residents of Meadow Valley and Bucks Lake are concerned that the tussock moth larvae — caterpillars — are creating a fire threat by defoliating the forests.

Huge swaths of brown-tinged white fir trees cover the ridges and slopes of Plumas National Forest, not only in the La Porte area (as featured in the Aug. 13 story Under Siege) but in the Meadow Valley and Bucks Lake areas as well.


This aerial photo map depicts the Douglas-fir tussock moth outbreak in the Plumas and surrounding forests. Map courtesy Plumas National Forest

Defoliation has also occurred throughout the Lassen, Modoc and Tahoe national forests.

The caterpillars eat the tips of young fir needles, causing the branches to turn brown and shrivel up.

According to a U.S. Forest Service press release, limited outbreaks of the Douglas-fir tussock moth were observed in northern California in 2013 and again in 2014. “Damage (defoliation) for 2014 has already passed, so no control is currently warranted. Evaluations will be conducted this fall to determine what, if any, defoliation might occur in 2015.”

The female tussock moth cannot fly, and stays on the cocoon after hatching. Females emit a pheromone to attract males. After mating, they lay eggs on the cocoon and die.

Thus, predictive evaluations include getting out in the forest and checking egg masses on the cocoons in the fall, according to entomologist Don Owen at California Department of Forestry and Forest Protection.

Owen has had many years of experience as a forest health specialist and has documented numerous tussock moth outbreaks, including one at Bear Mountain near Redding. He said that the fire danger in the short term on the Plumas is not all that great.

Owen said, “The message is that most of these trees that are brown and look bad will recover. It may not look like it now, but they will recover.”

Owen created a PowerPoint presentation, “White fir Recovery and Mortality Following the Douglas-fir Tussock Moth Bear Mountain Outbreak 2005-2007.” The study summarizes key data and presents dozens of photos taken of damaged trees in 2007 side by side with follow-up photos taken of the same white firs in 2009 and 2011.

To access this PowerPoint go to, click on Resources at the bottom of the page and choose the title listed above. Or call 805-550-8583 for more information.

Another excellent source for information on the Douglas-fir tussock moth is “Forest Insect & Disease Leaflet 86,” available from the U.S. Department of Agriculture Forest Service at

This leaflet describes the damage caused by DFTM and explains the life cycle of the moth. It lists several outbreaks and statistics, including an outbreak in the Blue Mountains of Oregon and Washington that killed 39 percent of all trees in the heavily defoliated areas.

Owen said that the Bear Mountain outbreak followed a typical three-year cycle — population release, peak and decline — and he thinks that what’s happening on the Plumas is similar.

He said that a “natural enemy complex” consisting of parasitic insects, predators and virus kicks into action during a DFTM outbreak during the second, or peak, year. The natural enemies attack young caterpillars and usually bring the outbreak to an end a year later.

“I have seen so many outbreaks up and down the state — you have these peak years, then the natural enemies exert a control in the third year.”

Owen said that from an ecological standpoint, the tussock moth caterpillar is taking advantage of a forest that’s a little out of whack. He said white fir is an understory species, and that by thinning out the areas too heavily concentrated, it might actually be helping the overall forest health.

Owen said he worked on the tussock moth outbreak in the late 1980s that occurred on Tamarack Flat in Meadow Valley. At that time they sprayed to help control the outbreak.

He said it is unlikely that a big spraying project like that one will reoccur. He said many people question whether the expense and risk to people and the environment posed by spraying is worth it.

Owen said he and entomologist Danny Cluck will be surveying affected areas of the forest, probably in mid-October. They will analyze egg masses and evaluate the likelihood of further defoliation.

He said that private landowners can choose to spray or log affected areas if they want to. But to his knowledge, timber companies in northeastern California are not planning to take such measures.

Public areas like the national forest can also choose to spray or log, but the public process takes much longer and involves more studies.

PNF Beckwourth Ranger District timber sale and contract specialist Thobe Oestreich said he doesn’t anticipate any timber sales as a result of the outbreak.

“We’re not anticipating mortality. We’ll just keep an eye on it,” he said.

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