Western Pine Shoot Borer – Eucosoma sonomana

Western Pine Shoot Borer (Eucosoma sonomana)

Latin Name: Eucosoma sonomana

Common Name: Western Pine Shoot Borer


  • Adults are coppery-red moths with two brilliant grey transverse stripes on their forewings and a wingspread of around 20 mm.
  • Shortened needles and slowed terminal growth are two external signs. Exit holes can be discovered in the middle of the stalk when the larvae emerge.
  • A year after infection, noticeable swelling around the stem, near the exit hole. Terminals might break off when the exit hole weakens the stem.


Throughout western North America

Host plants:

Ponderosa pine (Pinus ponderosae), Lodgepole pine (Pinus contorta) ,  Jeffrey pine (Pinus jeffreyi) and Engelmann spruce (Picea engelmanii).

Damages caused by Western Pine Shoot Borer:

Larval mining in the terminal shoots slows or prevents the elongation of the shoots and needles, which might affect the growth of new buds. Shoots are generally killed by larval mining in lateral shoots. Each terminal shoot attack inhibits yearly height growth by 25% and can potentially harm tree shape. The Western pine shoot borer attacks begin when trees reach around breast height (4.5 feet) and steadily grow over the next 25 to 30 years.

Life history and Habits:

Young larvae hatch from the eggs and penetrate shoots around terminal buds, where they mine downward in the pith, leaving no trace of their attack. By mid-summer, the larvae had completed their development. In most cases, each shoot has just one larva, which eats any circular exit hole in the bottom section of the shoot, falls to the ground, and pupates for the winter. Shoot borer pupae overwinter in ground litter under afflicted trees as cocoons.