40 



CIRCULAR 2 7 0, U. S. DEPARTMENT OF AGRICULTURE 



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. 



LIPE HISTORY 



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

 masses smTormding the twigs, each mass containing several hundred 



eggs covered with a frothy, waterproof 

 material. The young caterpillars 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 some- 

 what 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 hi various sheltered 

 places, such as under loose bark, in curled 

 leaves, or under projecting eaves of nearby 

 buildings. The cocoons are tightly woven 

 of vellow silk, surrounded with a loose mass 

 Fl nS E of 4 I^^n fent of «*■ The moths emerge in June, or July 

 caterpillar (Malacosoma and soon deposit the overwintering egg 

 americana F.). masses. 



CONTROL 



Many of the egg masses may be foimd and destroyed when the 

 trees are pruned. If the small caterpillars are numerous, a spray of 

 lead arsenate, 2 pounds to 100 gallons, applied just before the trees 

 bloom, is very effective. If the spraying is done later, the quantity 

 of lead arsenate shoidd be doubled, as the larger caterpillars are more 

 resistant to the poison. Very often the tents can be pruned out and 

 destroyed or burned out with a torch, moving the flame rapidly so as 

 not to injure the tree. The tents should be destroyed at night when 

 most of the caterpillars are congregated in them. 



Fall Webworm 

 Although the habits of the fall webworm (Hyphantria cunea (Drury)) 

 are somewhat similar to those of the tent caterpillar, there is enough 

 difference to remove any difficulty in distinguishing the two insects. 

 As the name implies, the fall webworm appears late in the summer 

 and constructs a loose and very un sightly nest of webbing about a 

 number of twigs (fig. 48). These nests are extended as the caterpillars 

 grow and often enclose entire branches. The caterpillars feed within 

 the webs, devouring the leaves and fruit. When full-grown the cater- 

 pillar is about 1% inches long, covered with long, whitish hairs, and 



