Buds and Shoot Insects

Western Pine Shoot Borer
Eucosma sonomana (Kearfott)

Host:  Ponderosa pine

Figure 161. Figure 161. Damaged (top) and undamaged (bottom) shoots of ponderosa pine caused by western pine shoot borer larvae. Note 'bottlebrush' appearance of damaged shoot.

Symptoms/Signs:  Adults are moths with coppery-red forewings marked with two bright gray transverse bands and a wingspread of about 20 mm. External symptoms include shortened needles and stunted terminal growth. Following emergence of the larvae, exit holes can be found near the center of the shoot. In the year following infestation, a distinct swelling can be seen around the stem, near the exit hole. Occasionally terminals break off where the stem is weakened by the exit hole.

Figure 162. Figure 162. Larva of the western pine shoot borer. Note that larval feeding is restricted to the pith region of the shoots.

Biology:  Eggs are laid on elongating shoots in spring. The larvae feed in the pith of these shoots, vacate in late spring, and drop to the ground to pupate. There they remain dormant through the winter and hatch as adults the following spring.

Effects:  Larvae mine only in the pith of the shoot. Usually shoots remain green for at least a year after attack, however, in some cases shoots are killed outright. Most often shoots live, but become stunted. Frequently, lateral shoots overtop affected shoots and a crook or a fork results. The main result of infestation is reduced height growth, about 25 percent of one year’s vertical growth per attack. Depending on management objectives, this may or may not be important. The insect occurs at low population levels.

Similar Insects and Diseases:  See pine tip moths.

References:  24, 96, 98