INSECT ENEMIES OF EASTERN FORESTS 563° 
q 
a) 
FIGuRE 154.—Cimbegx americana, the elm sawfly: A, Willow leaves showing loca- 
tion of eggs; B, twig showing incisions made by adult; C, egg; D, newly 
hatched larva; #, mature larvae; F, cocoon; G, open cocoon showing pupa; 
H, pupa, side view; J, mature sawfly; J and K, saw of female. OC, D, J, K, 
much enlarged, the others less enlarged. 
westward into British Columbia. Its principal food plants are elm 
and willow, but occasionally larvae are found feeding on alder, bass- 
wood, birch, maple, and poplar. The larvae are vigorous defoliators, 
and the adults sometimes cause injury by gnawing into the bark of 
twigs. This species is generally rather common in New England, 
and local outbreaks have been observed on the bush and tree willows. 
One year is necessary to complete a generation, and laboratory rec- 
ords show that sometimes a considerable number of prepupal larvae 
in cocoons may hold over in a diapause for at least 21 or 22 months. 
In New England the period for emergence of adults extends from 
about the middle of May to the middle of August. The eggs are de- 
posited in pockets cut into the leaf tissue by the female. Larvae may 
be found from June until October, although probably each completes 
its growth within 6 to 8 weeks. The full-grown larvae crawl to the 
ground and spin tough, brown papery cocoons in the litter or among 
the roots of grass and weeds in the topsoil. The winter is passed as 
