Observations on the Habits of an introduced Pine Sawfly, Diprion simile Htg.
Diprion similis, Htg., was recorded for the first time in Canada in Ontario in 1931, and larvae were observed on Pinus mugo [montana] in Montreal in August 1933. In preliminary observations during 1934 the overwintered larvae were found to pupate in mid-May, and adults were on the wing in late May and early June. The eggs of the first generation hatched in 10-14 days, and the larvae spun cocoons in the second or third week in July. The adults emerged after 11-16 days. The eggs of the second generation hatched in 7-8 days, but the period of larval development was lengthened by the low night temperatures during August, and most of the larvae did not spin their cocoons until mid-September. Some larvae pupated at irregular intervals throughout the season, and some may probably remain in their cocoons for one, two or three seasons. In the Montreal area, however, there seemed to be two well-defined generations. The infestation in 1934 was confined to two areas, but all species of pine commonly grown in Quebec are liable to attack. In experiments, Pinus mugo P. sylvestris, P. banksiana, P. resinosa and P. strobus were readily selected for oviposition, but P. strobus was preferred. In a plantation where overwintering cocoons were observed on P. strobus and P. sylvestris, most of them were either on the branches or on the needles. The severe winter of 1933-34 apparently destroyed all the cocoons formed on the branches of the trees, but enough of those on the ground and on the lower 3 ft. of the trunks survived to re-establish the infestation. A few of the summer cocoons were constructed on trees other than pine, low-lying shrubs and blades of grass. On the branches of the trees the cocoons were usually clustered at the bases of the smaller twigs. Those on the trunks were either in crevices of the bark or in the scars left by fallen branches.