TWENTY-SIXTH REPORT OF STATE ENTOMOLOGIST 35 



all of the leaf tissues leaving just the leaf ribs. The application 

 of a lead arsenate spray 1 pound to 50 gallons of water in late 

 April or early May, depending on the season, would give effec- 

 tive control. Annual spraying is not essential. It is safe to 

 advise spraying only following seasons of severe infestation, or 

 when the lower leaves of the plant exhibit many fine holes 

 from feeding by the young worms early in the season. 



THE FOREST TENT CATERPILLAR 



The most conspicuous insect on shade trees in 1936 was the 

 forest tent caterpillar (Malacosoraa disstria Hbn.) Along the 

 upper Yellowstone and particularly in Livingston's Island Park, 

 Cottonwood trees were completely defoliated by these insects. 

 Of the hundreds of trees in that park only one was noticed 

 which had been overlooked by the caterpillars. The trees sent 

 out new growth during the latter part of the summer and prob- 

 ably suffered no permanent injury but the appearance and use- 

 fulness of the park up to July was ruined. In the case of such 

 tall trees control is difficult if not impossible without proper 

 equipment for dusting or spraying the foliage rather early in 

 the season while the caterpillars are still small. At that time 

 they are easily killed by arsenicals. 



This species does not build a tent like its close relative the 

 apple tree tent caterpillar and for that reason has been named 

 the "tentless" tent caterpillar. The larvae instead of hiding 

 away in a tent congregate in great masses in the crotches of 

 the branches. They are about two inches long when full grown 

 and are a dusky brown in color with fine yellowish-brown 

 stripes on the back and sides. They are covered with long fine 

 brown hairs. There is but a single brood. Pupation occurs in 

 a silken cocoon attached to any convenient place on the trees or 

 nearby objects. The adult moths vary in color from reddish to 

 fawn, the males being smaller and much darker than the fe- 

 males. They emerge from the cocoons in midsummer and the 

 females deposit their eggs in rings around the smaller twigs. 

 The eggs develop into young caterpillars by fall but the young 

 worms do not leave the egg shell until the following spring 

 when the leaves begin to unfurl. 



