INSECT ENEMIES OF WESTERN FORESTS 99 



with a loss of timber estimated at 40 million board feet (fig. 40). 

 Airplane spraying with lead arsenate and DDT was used to con- 

 trol this outbreak. 



Although western hemlock is the preferred host, the caterpillars 

 appear in countless thousands when an outbreak occurs and feed 

 on any foliage at hand. Douglas-fir, Sitka spruce, and western red- 

 cedar may be heavily attacked when in mixture with hemlock; 

 also huckleberry, salal, and broadleaved forest shrubs and trees 

 are frequently eaten. In fact, when the caterpillars are exception- 

 ally numerous, nothing green is left on the infested areas. 



The moths of the hemlock looper are light buff, with a wing ex- 

 panse of about iy 2 inches. The forewings are marked with two 

 wavy lines and the hind wings with one wavy line. They fly, mate, 

 and lay eggs late in September and during October. The eggs are 

 about the size of a pinhead, blue to gray-green or brown with a 

 characteristic impression, and are attached to the moss on the 

 tree trunks, or to twigs or branches. The winter is passed in the 

 egg stage, and the eggs hatch the following spring. The young 

 larvae, which are about % inch long, crawl up the tree trunks and 

 start feeding on the young needles. The first feeding takes place 

 in May, June, and the early part of July and is not particularly 

 noticeable. However, from the middle of July to October the feed- 

 ing of the caterpillars causes a heavily infested forest to turn 

 yellowish red and then brown, as though scorched by fire. Late in 

 summer the caterpillars feed on the foliage, clip off small twigs, 

 crawl over the trunks, cling to shrubs, and drop by silken webs 

 from the trees to the ground. These silken webs may become so 

 abundant that the whole forest looks and feels like one big cob- 

 web. When full grown, the caterpillars are about 1% inches long, 

 green to brown, with diamond-shaped markings on the back. They 

 drop to the ground in August and September and secrete them- 

 selves in protected places, such as crevices of the bark or under 

 debris on the ground, and there transform to pupae. 



The mottled, greenish-brown pupae, about y 2 inch long, are 

 unprotected by a cocoon. The moths appear within 10 to 14 days 

 and during an epidemic are so abundant as to give the impression 

 of a snowstorm in the woods. Creeks, springs, and rivers are cov- 

 ered with the dead bodies, and tree trunks are plastered with them 

 until heavy rains wash them into the ground or carry them away. 

 There is one generation annually. 



Outbreaks of the hemlock looper usually last about 3 years, 

 after which they are generally brought under control by the action 

 of parasites, predators, and disease. A polyhedral virus disease is 

 particularly effective in decimating the caterpillars. Heavy rains 

 during the flight period reduce egg laying, checking an epidemic 

 and hastening its decline. 



Although nature will ultimately bring outbreaks under control, 

 a vast amount of timber may be saved if artificial control meas- 

 ures are applied to protect the trees from heavy defoliation. It has 

 been found that trees can recover from a 50-percent defoliation, 

 and in some cases a 75-percent defoliation is not fatal unless the 

 trees are subsequently attacked by bark beetles. At present, air- 



