The voracious tussock moth, an insect that feeds chiefly on white fir and Douglas fir, is plaguing prime Sierra timberlands east of Chico, the U.S. Forest Service said. “They will eat every needle off a tree and kill it in a year,” said John Neisess, chief pest control manager for California national forests. Tussock moth larvae are wind-borne, spinning hairs that blow into the trees, where they remain until they hatch. The caterpillars voraciously consume every needle of fir trees if they are not deterred. A quarter of the trees that are attacked usually die, Neisess said. Surviving trees can suffer permanent stunting or slowed growth. Hard red splotches mark timber stands infested by the insects in a 50-mile stretch reaching south of Lake Almanor in the Lassen and Plumas national forests, Neisess said. A commercially produced bacteria was used to combat the infestation last year, but “trouble blew up in a lot of other places,” Neisess said.