White pine weevils, Pissodes strobi, attack a number of the conifers in North Carolina. They are small (about a 1/4 inch long), brownish weevils marked with whitish and rusty patches. The curved snout is about 1/4 as long as the rest of the body. White pine weevil eggs are small, pearly white and translucent. Mature larvae are fat, yellowish-white, legless grubs with brown heads and 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 other parts of the country.
White pine weevils occur throughout eastern North America within the range of the primary host plant, white pine (Pinus strobus). This weevil infests other pines and spruces, especially Norway spruce. Adults overwinter in litter under host trees. They emerge anytime temperatures reach 65º to 70º F for a couple of days 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 of the terminal stem. The weevils chew a series of feeding holes in the stem of the leader causing the formation of several droplets of clear resin. These resin droplets are fairly obvious as they glisten in the sun. After making the initial series of feeding punctures, females move to the very tip of the leader to make more holes in which small, pearly white, translucent eggs are inserted. Larvae hatch 1 or 2 weeks later. These grubs often work downward as they feed on the cambium, completely girdling the leader. By late May, the larvae girdle the stem and the expanded candles wilt, forming a characteristic "Shepard's crook." By mid to late June, the larvae often burrow past last year's whorl of branches thereby killing the entire top set of branches of the tree. One or more of the top branches may grow upward to replace the leader, which results in a crooked or multiple trunk tree. As they mature, the grubs burrow into the pith and form a pupal cell although some grubs form chip cocoons just under the bark. About 2 weeks later the grubs pupate. Then after 12more 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. The new weevils feed on smaller branches of host trees, but usually doesn't cause significant damage although sometimes the adult feeding is severe enough to kill entire shoots. They then seek an overwintering site even though the weather may be warm.
White pine weevils have one generation per year so there is only one "window of opportunity" to prevent an infestation. Late April to early May is the best time to spray one of the pyrethroids labeled for landscape to kill or repel adult weevils emerging from under infested trees. Only the tops of trees need to be sprayed to protect the leader and upper lateral branches. However, this pest is usually first detected when the leader of a white pine suddenly wilts and turns brown as the white pine weevil grubs burrow down just under the bark. To help confirm that white pine weevil is the cause of the damage on white pine or spruce, 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. If an infestation of grubs is found, the infested portion of the leader should be pruned out and only one of the branches in the top (living) whorl of branches should remain so that this branch will grow upwards to replace the leader. Wrap a wide rubber band strip around the "leader stump" and the branch to be trained. This will hold the branch up and the rubber band will decompose over the summer and drop off. There is risk of girdling the branch if a wire or plastic strap is used and forgotten. This will result in the least disruption of orderly growth and shape.
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 imidacloprid, a systemic insecticide labeled for landscape use.
- Act Now to Control White Pine Weevil. Boggs, J. 2017. Buckeye Yard & Garden onLine. The Ohio State University.
- White Pine Weevil. Day, E. R. and S. M Salom. 2015. Virginia Polytechnic Institute and State University publication 444-270 (ENTO-113NP).
- White Pine Weevil. Hamid, A., T. M. ODell, and S. Katovich. 1995 (revised). Forest Insect & Disease Leaflet 21. U.S. Department of Agriculture Forest Service.
- White Pine Weevil, Pissodes strobi (Peck). Hoover, G. A. Sr. 2011 (revised). Penn State College of Agr. Sciences, Dept. of Entomology. Insect Advice from Extension. Fact Sheet.
- NC State Extension Plant Pathology Publications
- NC State Extension Horticultural Science Publications
- North Carolina Agricultural Chemicals Manual
For assistance with a specific problem, contact your local Cooperative Extension center.
Publication date: May 28, 1997
Revised: Oct. 22, 2019
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