INSECT ENEMIES OF WESTERN FORESTS 39 



Dioryetria dbietella D. and S. is a gxay moth about three-fourths 

 of an inch in length. The reddish caterpillars feed in the twigs and 

 cones of knobcone, lodgepole, western white, sugar, and ponderosa 

 pines, and many of the balsam firs. There appear to be two annual 

 generations. 



The Zimmerman pine moth {Pinipestis zhnmerrnani Grote), a me- 

 dium-sized moth, light to reddish gray, closely related to the above, 

 is reported by Brunner {9) as being destructive to all coniferous trees, 

 especially ponderosa pine, throughout the Pacific Northw^est. He 

 credits the "spike top" of mature trees and the spike top, stmiting, 

 and destruction of smaller trees, to the work of this insect. However, 

 its importance has probably been greatly overemphasized, as its dam- 

 age is usually negligible in most localities. 



PiNE-Trp Moths 



The pine-tip moths belonging to the genus Rhyacionia may cause 

 considerable damage to new leaders and shoots of young pine in lo- 

 calities where heavy infestation occurs, especially in plantations or 

 on cut-over lands where trees are openly spaced and growing on 

 sunny exposures. Trees from seedling size up to a heig-ht of about 

 25 feet are the most susceptible to injury. The small moths are yel- 

 low, gray, or reddish brown. They lay their eggs on the pine needles, 

 and the young caterpillars start feeding at the tips of shoots, bur- 

 rowing into the buds and down into the new growth. Their work is 

 characterized by a resinous exudation at the point of attack, but they 

 do not form a pitch nodule on the stem. Though trees are seldom 

 killed, they are often deformed or forked, and height growth is re- 

 tarded. Several species have been described from the Western States, 

 where they normally work on the tips of young forest trees. Two 

 species are particularly destructive in the pine plantations of the 

 Nebraska National Forest. 



Rhyacionia frustrana hushneUi Busck {28^^ 38 ^ 83) causes a limited 

 amount of damage to seedlings and saplings in its native range in the 

 Black Hills, the Lake States, and northwestern Nebraska but has done 

 serious damage where introduced in the isolated pine plantations of 

 the Nebraska National Forest. In the ponderosa pine plantations 

 of this forest about 90 percent of the leaders have been injured an- 

 nually for many years by this tip moth. The adult moths are small, 

 with a wing spread of about one-half inch. The front wings are 

 mottled with yellowish gray and reddish brown. The larvae are 

 yellowish and when full grown are nearly a half inch long. A single 

 generation occurs in the Black Hills, the moths flying late in May 

 and early in June to lay their eggs on the pine needles, and the larvae 

 feeding during June and July. In Nebraska two generations de- 

 velop annually, the moths flying in April and May and again late in 

 June and early in July. The winter is passed in the pupal stage in 

 cocoons spun by the larvae in the litter or soil. 



Rhyacionia neomexicana Dyar has caused considerable injury to 

 ponderosa pine seedlings and saplings at various places in the South- 

 west and is becoming a serious pest at present in the Nebraska Na- 

 tional Forest plantations. It is known to occur in New Mexico, 

 Arizona, southern and eastern Colorado, the Black Hills, and Ne- 



