White pine weevil
Publication date: May 10, 2019Pissodes strobi
Adult white pine weevils are brown with white spots. This species of weevil is found in spruce and pine ecosystems throughout Canada. White pine weevil or spruce leader weevil is a weevil in the family Curculionidae (weevils or snout beetles) in the order Coleoptera.
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Description
In early spring adult weevils make short flights to disperse after overwintering. Adults females lay their eggs at the tip of the previous year’s leader in spring. The eggs are laid inside the female's feeding hole and then packed in place with fecal matter. The larvae hatch and feed downwards along the leader. The feeding kills the leader and it curls into a characteristic “shepherd’s crook” form.
The larvae pupate in chip cocoons at the base of the leader and new adults emerge in August or September of the same year. If weather conditions are unfavorable, then larvae or pupae may overwinter and emerge in the following spring. The life cycle is completed within one year.
Once a suitable host tree is identified, successful attack depends on weevil numbers and host suitability. Weevil larvae must be present in sufficient numbers overcome the host tree’s defense effort.
Host tree species
White pine weevil attacks several commercially important conifer hosts. The most important hosts in British Columbia are sitka spruce, Engelmann spruce and white spruce. Other hosts in North America include eastern white pine (Pinus strobus), Jack pine, and Norway spruce (Picea abies).
Damage symptoms
This weevil damages the tree leader which is the new growth formed over the past two years.
Weevil damage can cause a forked or dwarfed tree form, and repeated attacks can cause severe stem deformation over time. Weevil attacks can cause growth losses, a reduction in wood quality, a decrease in lumber recovery and potential tree death.
Management
Weevil outbreaks are facilitated by monocultures of host trees on warm, highly productive sites. Management recommendations for controlling weevil outbreak include:
- Dense replanting of host trees
- Planting non-host species
- Planting a species mixture that will provide deciduous overstory (shading) for the developing host trees
Although it is unlikely that these methods will completely eliminate the weevil from commercially important plantations, the impact of weevil damage may be reduced.
Tree breeding programs initiated by the British Columbia Ministry of Forests have focused on the identification of resistance traits in Sitka spruce. Planting resistant host trees in highly susceptible areas can also reduce damage.
Identification images
Weevil on a pine leader
Close-up of an adult weevil
Damage caused by a white pine weevil to a spruce
Further reading
For more information about the white pine weevil, read the Field Guide to Forest Damage in B.C. (PDF, 6.5MB)