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



wasps, sarcophagid beetles, mites, and birds. Some of these have 

 proved very effective in holding it in check. From 1929 to 1934, 

 five species of parasites of European origin were colonized and 

 liberated in Washington. Four of these have become established 

 and at least one, Apanteles solitarius Ratz., has become abundant 

 enough to show apparent effect. 



Direct control is obtained by spraying the trees in the spring 

 with a stomach poison, such as lead arsenate. When egg masses 

 are exceptionally abundant they should be treated with creosote. 



TENT CATERPILLARS 



Tent caterpillars (Malacosoma spp.) (1^9), which are responsi- 

 ble for the defoliation of many different species of trees and 

 shrubs, can be recognized by the large compact webs at the ter- 

 minals of branches, which are such a common sight during April 

 and May. The various species are indigenous to this continent, 

 being widely distributed over the United States. Outbreaks were 

 recorded from Massachusetts as early as 1646. Coniferous trees 

 are sometimes attacked, but the preferred hosts are deciduous 

 trees and shrubs. While large forest areas are sometimes defoli- 

 ated, the resultant damage is usually of no great importance, since 

 deciduous trees can readily recover from the loss of foliage. 



The caterpillars that construct the tents are usually yellow to 

 brown, with rows of blue or orange spots and lines, and are lightly 

 covered with long hairs. A heavy, silk-lined cocoon is usually 

 formed in bark crevices or in leaves webbed together. The adults 

 are tawny yellow or brown moths, or millers, and are frequently 

 seen flying about lights at night. 



Tent caterpillars usually have but one generation a year. Adult 

 moths appear in midsummer and deposit masses of eggs in bands 

 encircling small twigs. The eggs do not hatch until the leaves ap- 

 pear the following spring. The young larvae feed on the new 

 foliage, construct the large tents on terminal branches, and reach 

 maturity early in the summer. They then form pupae, and the 

 adult moths appear soon after. 



Aside from the several species of predaceous beetles and bugs 

 that feed on the caterpillars, there are parasitic insects that lay 

 their eggs within those of the moth, and their minute larvae de- 

 velop within the host eggs and destroy them. Further control is 

 accomplished by parasitic insects that breed within the caterpillars 

 and the pupae. Birds also play an active part in controlling the 

 tent caterpillars, many species feeding on the caterpillars, others 

 feeding on the eggs, and still others on the moths. Often the most 

 complete control is accomplished by a wilt disease that rapidly 

 spreads among the colonies of caterpillars and leaves few sur- 

 vivors. 



There are six common species of tent caterpillars in the West, 

 and they are most easily distinguished in the field by the markings 

 on the larvae. 



The forest tent caterpillar (Malacosoma disstria Hbn.) is dusky 

 brown with a row of diamond or keyhole-shaped white spots along 

 the back and sides and with fine brown hairs. It feeds in large 



