574 MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
defoliating large stands of trees two or more years In succession. In 
such outbreaks an enormous mortality of trees is usually the result, 
especially when an infestation of the eastern larch beetle (Dendroc- 
tonus simplex) is associated with the sawfly infestation. During the 
outbreaks in the early eighties, widespread destruction of larch, espe- 
cially in mature stands, occurred throughout the Northeastern States 
and the eastern provinces of Canada. 
The adults emerge from late in May to early in July, and the females 
lay their eggs in slits cut in the young twigs of the larch. During 
periods of heavy infestation the oviposition injury causes a marked 
twisting of the growing twigs. The eggs hatch in about a week. The 
young larvae feed at first along the edges of leaves that arise from 
twigs of the previous year’s erowth, and later devour entire leaves 
on all parts of the trees. The larvae usually become full grown in 
July or August, depending on the climatic range. Sometimes larvae 
are found well into September, and laboratory. records indicate that 
occasionally there may be a partial second generation. When full 
grown the larvae spin tough, brown cocoons in the duff on the ground 
beneath the trees, in which they pass the winter (fig. 162). 
FicgurE 162.—Larvae and cocoons of the larch sawfly (Pristiphora erichsonii). 
(Courtesy Conn. Agr. Expt. Sta.) 
A hymenopterous parasite, J/esoleius tenthredinis Morley, a natu- 
ral enemy of the larch sawfly in Europe, has been introduced into 
Canada and the United States and is now firmly established in these 
countries. This species is more fully discussed on page 603. Rodents 
are important predators on this insect, destroying vast numbers of 
cocoons. Diseases affecting the larvae and the cocoons sometimes 
take a tremendous toll, especially when conditions are tavorable for 
epidemics. 
