38 



CIRCULAR 270, U.S. DEPARTMENT OF AGRICULTURE 



infestation is severe a second application may be made 10 days or 2 



weeks later. 



WESTERN TENT CATERPILLAR 



The western tent caterpillar (Malacosoma pluvialis Dyar) is prac- 

 tically limited in its depredations to the region west of the Cascade 

 Mountains. The caterpillars appear in May and June, constructing 

 tents of webbing in the crotches or about the smaller twigs and leaves 

 of the trees. (The tents are similar to those of the eastern tent cater- 

 pillar shown in figure 47.) The caterpillars feed voraciously during 

 the day, devouring all of the leaf tissue except the midribs, and retire 

 at night to the tents, or collect in masses on the larger limbs. These 

 caterpillars occur sporadically and in some years are numerous enough 

 to defoliate not only fruit trees but wild growth and shade trees as well. 



LIFE HISTORY 



The insect passes the winter in the egg stage. The eggs are laid in 

 masses surrounding the twigs, each mass containing several hundred 



Figure 46.— Young pears injured by the syneta leaf beetle. 



eggs covered with a frothy, water-proof material. The young cater- 

 pillars appear about the time the apple buds begin to open. The 

 group hatching from a single egg mass constructs a small silken nest 

 or tent, and as the caterpillars grow this nest is enlarged to provide 

 adequate protection for the colony. The caterpillars are somewhat 

 hairy, tawny brown, with a row of blue spots flanked by orange spots 

 along the back. When full grown they are nearly 2 inches long. As 

 the caterpillars become larger they tend to scatter, and their cocoons 

 may be spun in various sheltered places, such as under loose bark, in 

 curled leaves, or under projecting eaves of nearby buildings. The 

 cocoons are tightly woven of yellow silk, surrounded with a loose mass 

 of silk. The moths emerge in June or July and soon deposit the 

 wintering egg masses. 



