THE LARGE LARCH SAWELY. 51 
the next year, when they turn to pupa, the adults issuing in due 
course. 
There is no evidence, so far, that there are two generations in 
the year, and yet the caterpillars seem to attain full size in 
a comparatively short time. It is interesting and sometimes 
puzzling as to why, from cocoons collected and _ possibly 
made at the same time and kept in the same conditions, 
there should be such variations in the escape of the adults. 
For example, in my recent experiments with Lophyrus pint, 
the pine sawfly, in 1905, from cocoons collected in the winter 
of 1904 and kept indoors, 117 adults issued, these insects — 
appearing on thirty-seven different days between April and 
August, the first coming away on April 14th and the last on 
August 1st. In 1906, from a number of cocoons made by 
the caterpillars in confinement in 1905, and kept indoors, 
104 adults issued, the insects appearing on thirty-two separate 
days, the earliest on the 1st of June and the last at the end 
of the first week of August. The practical import of this 
is that, as egg-laying takes place at different times according 
to the different flight-times of the adults, infestation must 
be expected not merely at some limited definite period, but. any 
time during the summer when the temperature is favourable. 
Age of Tree Attacked.—Infestation in the larches in Cumber- 
land was upon trees of from twenty to seventy years of age. 
The records elsewhere show that young plants of ten years of 
age may be attacked, but attack has been reported more 
frequently on older and taller trees. In one case in Washington 
County, United States, larches less than 25 feet high had been 
spared, but of those of 30 feet and upwards go per cent. had been 
attacked and almost completely defoliated. The fact that the 
caterpillars work on well-grown trees, and it seems character- 
istically at the crown first, increases greatly the difficulty of 
fighting them. 
Preventive and Remedial Measures.—1. As against the adults 
scarcely anything can be done effectively. They lay high up, 
well out of reach, so that the placing here and there of tarred 
boards standing erect and with the tar frequently replenished, 
which is practised sometimes against sawflies that lay on young 
plants, cannot be tried with hope of success. 
2. If young trees chance to be affected with the caterpillars, 
the caterpillars, especially when they are small and, it may be 
