Authors: Eric R. Day and Scott M. Salom, Virginia Polytechnic Institute and State University

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Cucujiformia
Superfamily	Curculionoidea
Family	Curculionidae
Subfamily	Molytinae
Tribe	Pissodini
Genus	Pissodes

Scientific Name

Pissodes strobi

Common Name

white pine weevil

Distribution and Hosts

The white pine weevil (WPW) is found throughout North America, Europe and northern Asia. Its preferred hosts are Eastern White Pine and Norway and Sitka Spruces, but it can attack Scots and other pines as well.

Description of Damage

The WPW usually attacks only the upright terminal leader. The previous year's leader (first whorl) and the new growth both die from the attack. Damage is first evident in March or early April when overwintering females chew holes in the leader for feeding and egg laying. These holes, 20-25 cm below the terminal bud, produce resinous bleeding that eventually dries to a white crust. By late May or early June, the larval damage is evident as the current year's leader droops like a shepherds crook, turns pale yellow and then brown. In July, the attacked shoot will have 3 mm diameter exit holes and tunnels and sawdust under the bark. A lateral shoot will eventually take over as the terminal leader but may have to be trained and have competing shoots removed. Trees of medium size, 1-12 m tall, are most commonly attacked. WPW is a serious pest of forest plantations, Christmas tree farms, yard plantings, and landscapes.

Identification

The immature stage found in the leader is a small, creamy-white, legless grub with a dark brown head. The adult is a small brown weevil 4-6 mm long. It is covered with irregular shaped patches of brown and white scales. Near the end of each wing cover are a large white patch and a brown patch.

Life History

One generation of WPW occurs per year. Adults remain hidden and overwinter in the litter on the ground or other protected places after emerging from infested terminal shoots in July. When the weather warms in March, they become active and fly to the upright leaders of the host trees. Adults feed for seven to ten days by chewing tiny holes in the bark. They then begin to deposit eggs individually in their feeding punctures. Within several days, the eggs hatch and the tiny larvae begin feeding under the bark, within the shoot, and down the stem. During this time, terminal buds open and new shoots develop normally. As the larvae become larger and the tunneling more extensive, the new growth wilts, droops, and by early July turns brown. By the end of June or early July, the larvae enter the pupal stage and transform to adults that chew their way out of the stem. Adults may fly in summer and fall, but they usually seek hibernation sites in the ground litter. They do little if any feeding until the following spring.

Control for Homeowners and Backyard Situations

Remove and destroy the infested top of the tree in the late spring before weevils emerge and seek hiding sites. In early March, treat the top sections of the tree with an insecticide such as permethrin. This will interrupt the egg laying by the adults and establishment of larvae.

Control for Commercial Production

Scouting

Look for resinous bleeding in late March or early April to find when adult females are feeding and laying eggs. Also check trees in June to determine which tops are actively infested with WPW. Check for a final time in the fall to determine the percent of trees that are infested.

Threshold for Christmas Tree Farms and Forestry Plantations

If fall surveys indicate that more than 5 percent of the trees were infested with WPW the previous season, plan on treating the whole plantation or block.

Mechanical Control

Prune out and destroy infested tops in late June. Make sure stems are cut below where weevils are feeding. Tops must be cut before the weevils make exit holes and leave.

Cultural Control

Remove all old unattended stands of white pine and Norway spruce that may be harboring populations of WPW.

Chemical Control

Treat the terminal leader with a registered insecticide before the buds open. Do not treat the lateral shoots, as they are not the infestation points. Apply the insecticide no later than late March or early April. For valuable specimen trees it may be necessary to treat each year. Consult the latest Horticultural and Forest Crops Pest Management Guide, Virginia Cooperative Extension publication 456-017, for current labeled insecticides.

Remarks

Repeated terminal dieback caused by WPW can give trees an asymmetrical crooked appearance that is aesthetically pleasing to many people. Often the nice old gnarly pine tree has been given its appearance by repeated attacks of WPW.

References

Day, E.,Salom, S. White Pine Weevil. Publication Number 444-270, Revised 2003. http://www.ext.vt.edu/pubs/entomology/444-270/444-270.html.
University of British Columbia. Pissodes strobi (Curculionidae). The Sitka spruce weevil (white pine weevil). http://www.forestry.ubc.ca/fetch21/FRST308/lab4/pissodes_strobi/sitka.html

Importance

The white pine weevil is the most serious insect pest of eastern white pine. Weevil larvea kill the last two-year's terminal growth and repeated attacks cause trees to become stunted and deformed to the point of being commercially unusable. Trees up to 3 feet tall may be killed. The weevil also attacks Norway spruce and jack pine and, to a lesser extent, pitch pine, red pine, Scots pine, and red spruce. It is found throughout the range of eastern white pine.

Identifying the lnsect

Adult white pine weevils are brown beetles about 1/4 inch (6 mm) long. They have a long snout with antennae attached. White and tan spots of various sizes cover the body. The most conspicuous spots are towards the back of the wingcovers. Full-grown larvae are legless grubs with reddish-brown heads. They are 1/2 inch (12 mm) long.

Identifying the Injury

In the spring, resin droplets ooze from feeding punctures on the terminal shoot, especially near the terminal bud. The most conspicuous sign of current weevil damage is a drooping of the terminal shoot caused by larval feeding. In the South, this "shepherd's crook" is usually noticeable in early June and by August it turns reddish brown. The terminal shoot dies, and one or more branches in the uppermost live whorl will assume dominance. This gives the tree a forked, crooked, or bushy form.

Biology

Adults overwinter in the litter beneath host trees and emerge in the spring to feed on the leaders of their hosts. Females deposit eggs in small punctures in the bark of the leaders. The young larvae bore downward, side by side, in a ring. After feeding for 5 to 6 weeks, the larvae construct pupal chambers in the wood or pith of the terminal shoot, and cover themselves with shredded wood and bark. New adults leave the tree by late summer and do some feeding before overwintering. There is one generation per year.

Control

Control of the white pine weevil is difficult. It is possible, however, to reduce the damage by making conditions in a young stand unfavorable for egg laying. Pine grown under a canopy of hardwoods is relatively free of weevil damage but requires intensive management. Under certain circumstances, insecticides can be used to protect the tops of trees.

Gallery

References

Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html