The elm sawfly, Cumbex americana Leach, is the largest of the 
North American sawflies. It is widely distributed, occurring from 
coast to coast in southern Canada and throughout the Northeas- 
tern States west to Colorado. The larvae feed primarily on the 
foliage of elm and willow, but are also observed occasionally on 
basswood, birch, maple, poplar, and alder. The antennae of the 
adults are tinged with orange, the head and thorax black, the 
wings smoky brown, and they are about 25 mm. long. The female’s 
abdomen is usually steel-blue, with three or four yellowish spots 
on each side and a faint whitish spot near the thorax. In the male, 
the whitish spot near the thorax is distinct, but there are no 
yellowish spots on the sides. Full-grown larvae are yellowish- 
white or greenish-white and about 48 mm. long, with a pebbly 
skin and a black dorsal stripe. While feeding, the larva usually 
coils its rear end around a stem or twig; at rest it usually lies 
coiled up like a snail fig. 175). 
COURTESY CONN. AGR. EXPT. STA. 
FIGURE 175.—Larva of elm 
sawfly, Cimbex americana. 
Adults appear from about mid-May to mid-August, and the 
eges are deposited in pockets cut into leaf tissues. Larvae occur 
from June until October, depending on location. When they be- 
come full-grown, they crawl to the ground and spin tough, papery 
cocoons in the litter or just below the surface of the soil. Winter 
is spent in the larval stage, and pupation occurs in the spring. 
There is one generation per year. 
The elm sawfly is of minor importance as a defoliator of forest 
trees, but occasionally seriously defoliates shade tree elms. Willow 
also has been heavily attacked in the Northern Great Plains area. 
The larvae partially or entirely defoliate the trees, while the 
adults chew the thin, tender bark of twigs, girdling and killing 
them. 
Trichiosoma triangulum Kirby occurs fairly commonly in the 
Eastern States. The larvae are solitary feeders on the foliage of 
birch, poplar, willow, and wild cherry. At maturity, they are 
about 37 mm. long. The head is creamy white, the body greenish- 
white, and the eye spots and spiracles blackish. The life cycle is 
similar to that of the elm sawfly. 
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