7
ders of dense stands wherever the soil and other conditions are most favorable for rapid growth.
The unfavorable conditions for injury are slow growth, dense pure stands, and mixed stands of pine and hardwood.
Under the former conditions the thrifty, vigorous terminals are especially favored as breeding places for the weevil; and where these are killed, the vital energy of the tree is thrown into the lateral branches. Open stands, therefore, favor the development of large branches and a spreading crown, while under conditions unfavorable to weevil injury the terminals are smaller and, even if they are killed, the close stand or lateral shade will tend to produce an upward or vertical growth of the topmost branches, the stronger one taking the lead and soon repairing the damage.
NATURAL ENEMIES.
Numerous parasitic and predatory insect enemies attack the developing broods in the terminals. Woodpeckers, also, feed on the matured
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Fig. 6.—Barrel for terminal shoots infested by white-pine weevil, with wire screen over end allowing escape of parasites but preventing the escape of weevils. (Original.)
larvæ, pupæ, and adults. Some of the larvæ apparently die from disease, and when the large numbers of them are crowded together the larger ones appear to feed on the smaller ones, so that on the average not more than from 3 to 5 per cent of the hatched larvæ ever reach maturity and emerge from the infested terminals. However, each female is capable of depositing more than one hundred eggs each year for several years; thus the depredations are continuous. During some years the damage will be slight, while in other years it will be very severe, the amount of injury depending on the number of adults that survive and the conditions presented for their attack and development.
METHODS OF CONTROL.
It will be seen that in the successful control of this pest, as in the control of forest insects in general, much depends on special features in
