WHITE PINE WEEVIL
Mature larvae are yellowish-white, legless grubs with brown heads. They are 3/16 to 1/4 inch long. White pine weevil pupae are creamy white and 3/16 to 1/4 inch long. This insect is also known as the sitka spruce weevil and Englemann spruce weevil.
In mid June, infested branches begin to wilt. One or more of the top branches grow upward to replace the leader which results in a crooked or multiple trunk tree. Adults feed on the buds and bark to a limited extent.
Adults overwinter in litter. In mid to late spring after new growth
has emerged on white pines, the adults emerge and crawl or fly to the new
top growth. These weevils feed on the succulent bark 7 to 10 inches below
the top most bud. Eggs are deposited in a ring around the leader in about
a week. The larvae hatch 1 or 2 weeks later. The larvae often work downward
as they feed on the cambium, completely girdling the leader. As they mature,
the grubs burrow into the pith and form a pupal cell. Some grubs form chip
cocoons just under the bark. Two weeks later the grubs pupate. Then after
twelve more days the new adult molts from the pupal skin. Development takes
7 or 8 weeks. The new adults eventually chew out through the bark of the
dead leader and feed for a short time on the new buds or young growth.
They then seek an overwintering site even though the weather may be warm.
To help confirm that white pine weevil is the cause of the dead white pine or spruce top, use your fingernail and scrape back the bark in the affected area. The bark will be very loose and a dark, moist, powdery material will be present under the bark. As you scrape further down, you should find oval patches of excelsior-like material, about 1/2-inch long. After removing this material from the patch, you will find an area in the sapwood that has been hollowed out. This is the "chip cocoon" of the weevil. You may even find the pupae or yet-to-emerge adults within the cocoon.
Following the emergence of new tree growth, if feeding punctures from the adult are observed, a pesticide may be sprayed on the leader to protect it from egg laying. Chemicals containing cyfluthrin or diflubenzuron may be useful protectants when timed correctly. Whenever adults are observed on the leaders of small white pines, adult weevils may be collected by jarring the tree, causing the weevils to tumble down. The weevils may be destroyed by drowning them in a solvent or by some other means. Tests in Ohio are showing some protection with imidicloprid.
More information on this insect may be found
USDA FDI Leaflet 21
Ohio State Information Note
Prepared by: James R. Baker & S. Bambara, Extension Entomologists
Some information provided by Dave Shetlar, Ohio State University
Published by North Carolina Cooperative Extension Service
© 2001 NC Cooperative Extension Service
Web page last reviewed January, 2011 by the webperson.