Red pine cone beetle

The red pine cone beetle, Conophthorus resinosae, occurs in southeastern Canada and the northern tier of states from Maine to Minnesota. This insect was found on red pines in Crow Wing County just north of Brainerd this August. It breeds by preference in second-year red pine cones, but also attacks current-year red pine shoots. It occasionally attacks second-year jack pine cones. The adult beetle is shiny black, with sparse short fine hairs, and it is about 1/8 inch long. Damage by C. resinosae is often severe enough to make the commercial collection of red pine seed impractical or impossible.

Seasonal activity begins in May when the overwintering adults emerge and attack current-year shoots and second-year cones of red pine. The adults feed for a few weeks and then move to cones for oviposition purposes. Cones are entered by females near the petiole on the underside, often forming an open groove at the cone base. The tunnel is excavated in the pith to the end of the cone. Eggs are deposited singly in niches along the sides of the tunnel. After oviposition is completed the female returns to the base, fills the base of the tunnel with a plug of resin and debris, then vacates the cone. Infested cones soon wither, harden, turn brown, and occasionally drop from the tree.

The larvae feed on seeds and scales in the cone and pupate in frass-lined cells which often are near the base of the cone. During late summer new adults emerge through the plugs in the bases of the tunnels, through the top or sides of the cones. Soon after emergence they bore into current-year red pine shoots and tunnel forward through the pith into vegetative buds where they spend the winter. Weakened at the point of beetle entry, the shoots soon break off and fall to the ground. When cones are scarce, the beetles can complete their life cycles in red and jack pine shoots. There is one generation per year.

Since these beetles overwinter in the shoots which fall to the ground they can be fairly well controlled by raking and disposing of these fallen shoots and any fallen cones.