No. 4.] SHADE-TREE INSECT PROBLEM. 



91 



pest of no mean rank. Fortunately, however, its increase 

 is largely controlled by parasites, which, when the caterpil- 

 lars are numerous, soon gain the ascendency. This accounts 

 for the occurrence of the insect in force only at somewhat 

 extended intervals. 



The white, froth-covered eggs of this insect are com- 

 mon objects on the trunks of trees chosen as food plants. 



a«£(D£Marw &tf 



Fig. 7. Different stages of the tussock moth : a, caterpillar; b, female pupa; c, male 

 pupa ; d, male moth ; e, same, wings spread; /, female moth ; g, female moth on cocoon ; 

 h, egg mass with froth over it ; i, cocoons on tree trunk ; A-, same, showing females and 

 egg masses also ; all slightly enlarged. — From Howard, Yearbook, United States De- 

 partment of Agriculture, 1895. 



The egg masses are laid by the wingless female moths, — 

 mere spider-like creatures, — in late summer or fall, on the 

 old cocoons, and are covered with a brittle white varnish. 

 The number of eggs laid by a single female ranges from 75 



