106 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



In the Pacific Northwest western hemlock and Pacific silver fir 

 appear to be the preferred hosts, although grand fir, alpine fir, 

 Douglas-fir, and Sitka spruce are also attacked during outbreaks. 

 In this area on the Olympic Peninsula of Washington, two or more 

 outbreaks have been recorded in which thousands of acres of west- 

 ern hemlock have been severely defoliated. Fortunately, these out- 

 breaks have resulted in the killing of very little merchantable 

 timber. In contrast, an outbreak in 1940-44 in the northern part 

 of Vancouver Island, British Columbia, killed a vast amount of 

 hemlock. 



The small moths, gray or dappled with brown, black, orange, 

 and white, have a wing expanse of 3 4 inch. They appear during 

 August and September, mate, and lay their eggs on the under side 

 of the needles. The eggs remain unhatched during the winter, but 

 in the spring the small, pale caterpillars appear and start feeding 

 on the new foliage of opening buds. They work in much the same 

 way as the spruce budworm, boring into and feeding on the open- 

 ing buds and webbing the new needles together to form a protec- 

 tive case within which they feed. As they develop they become 

 bright green, and the head turns black. If disturbed they actively 

 wiggle backwards and drop to the ground by silken threads. They 

 reach full growth by the last of July, at which time they are a 

 trifle more than y 2 inch long and may have brown heads. 



Usually they confine their work to the new growth, but if they 

 are numerous the larger caterpillars will leave the nests and feed 

 on the older needles, bringing about complete defoliation. Pupation 

 takes place within a web made among the dead needles and frass 

 on the twigs. Prior to emergence, the pupa, which is dark reddish 

 brown with a greenish tint, works partly out of the web so as to 

 allow the moth freedom to emerge. There is but one generation a 

 year. 



The black-headed budworm does a little feeding every year, but 

 its work is scarcely noticeable. When an attack is heavy toward 

 the end of July, the forest takes on a reddish-brown appearance. 

 This is due to the dying of the new foliage that is partly eaten but 

 remains attached to the twigs by the webs of the caterpillars. The 

 small, wriggly, green caterpillars or the brown pupae can be 

 found among the webs at the tips of the branches. For some rea- 

 son outbreaks of this insect on the Olympic Peninsula, which have 

 caused heavy defoliation of hemlock stands over vast areas — even 

 repeated defoliations for two or more years — have killed little or 

 no timber, whereas similar outbreaks on Vancouver Island, a lit- 

 tle farther north, have been disastrous. Comparable defoliation by 

 the hemlock looper apparently is much more damaging than that 

 by the black-headed budworm. 



The larvae of the black-headed budworm are parasitized by 

 numerous insects and are affected by a polyhedral virus disease. 

 These agents become dominant and bring outbreaks under control 

 within 2 to 3 years. 



The pine tube moth or lodgepole pine needle tier, (Argyrotaenia 

 pinatubana Kearf.) (26) (fig. 46) is found in the Rocky Mountain 

 region, where it works on lodgepole and whitebark pines. Usually 



