Outbreaks of the hickory bark borer occur periodically throughout the northeastern United States, and during the past five years many hickory trees in this vicinity have died.
The adult is a small black beetle appearing in May and June, which eats holes in the axils of the leaf stems causing them to fall early--usually in July and August. Brood galleries are then made longitudinally just under the bark of the trunk by the female, and a row of eggs is placed along either side of this brood chamber. On hatching the grubs, which are at first very small, tunnel at right angles to the central chamber, each making its own separate gallery. These galleries never meet or cross each other, but must necessarily diverge toward their extremities as they become larger. The effect of this is to girdle the tree which soon dies. The larvae pass the winter under the bark, finish their development in the spring, pupate, and the adults emerge in May and June from small round holes about the size of bird shot.
For control measures, Dr. Hopkins advises examining the trees during the fall and marking all dead and dying trees within an area of several square miles. Then between October 1 and May 1, cut all such trees and dispose of the infested portion to destroy the insects before the adults emerge.
Many forms of treatment have been devised and recommended by tree doctors for the control of this insect. Some of them may be worth trying; most are of doubtful value, and some are absolutely injurious to the trees. On July 3, 1914, some affected hickory trees on the Station grounds were sprayed heavily with powdered lead arsenate, 4 lbs. in 50 gallons of water, to which one pint of "Black Leaf No. 40" was added. Two days later many dead beetles were found on the tar walks under the trees, and a few were observed each day up until about the middle of August. Most of the trees treated, however, had been so badly injured by the insect that they were removed. Since then this insect has caused little damage on the grounds, though a few hickory trees still remain. In 1901 an outbreak of the hickory bark beetle caused the death of 110 trees on the Hillhouse place in New Haven; then the destructive work of the insect ceased and the few remaining hickory trees are still standing and in fairly good condition. I mention these instances to show that nature's control methods through parasites and natural enemies is far more effective with certain pests than any which man has yet devised. Of course, we hope that in the future man will make better progress along this line.