White pine weevil

Written by V.G. Nealis Revision 2024

• French common name: Charançon du pin blanc
• Other common names: Spruce weevil
• Scientific name: Pissodes strobi (Peck)
• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Coleoptera
• Family: Curculionidae
• Partial list of synonyms:
  • Pissodes engelmanni Hopkins
  • Pissodes sitchensis Hopkins

General information and importance

White pine weevil is a widespread, native insect of young pine (Pinus) and spruce (Picea) trees in North America. Originally, it was thought there were two additional related species attacking Sitka (P. sitchensis) and Engelmann (P. engelmannii) spruce in the west. It is now recognized that there is a single species with a transcontinental gradient in preferred native hosts from predominantly pines in eastern forests to mainly spruce in the west. In mid-continental Canada, both jack pine (P. banksiana) and white spruce (P. glauca) are attacked.

Before large-scale logging operations in the late 19^th century, white pine weevil was a relatively innocuous inhabitant of forest edges and gaps. It occupied areas where young trees grew in temporary, open conditions. These situations were scarce, and so was the weevil. These conditions changed, however, with accelerated harvesting and plantations for afforestation and reforestation. The open, warm conditions and concentration of susceptible age classes in these plantations favoured an increase in white pine weevil populations and subsequent increases in damage.

Distribution and hosts

The distribution of white pine weevil in North America coincides with that of its primary hosts; eastern white pine (P. strobus), jack pine, white spruce, Engelmann spruce, and Sitka spruce. This results in a transcontinental distribution in Canada and extends south to the United States. The American range includes the eastern United States to the northern forests of mid-Atlantic and Lake States, and the Pacific Northwest and Rocky Mountains to Colorado.

Secondary hosts include several other pine and spruce species including non-native Norway spruce (P. abies), blue spruce (P. pungens), and Scots pine (P. sylvestris), especially in plantations for Christmas trees and landscape ornamentals.

Host parts affected

Previous and current years’ leaders

Symptoms and signs

Adult white pine weevils are dark brown beetles. They are 6 to 7 millimetres long and are covered in white and tan spotted scales. They have the characteristic snout of weevils. White pine weevil may be confused with related bark weevils such as the lodgepole pine terminal weevil, Pissodes terminalis, in western North America. The symptomatic distinction is that white pine weevils attack previous year’s leaders and feed downward, whereas lodgepole pine terminal weevils attack current-year leaders and feed upward.

In early spring, resin flow may be evident from feeding pits made by adults on the leader (or leaders) just below the terminal bud. Eggs are laid in some of these pits and plugged with macerated phloem. Once the brood is established, larvae feed downward under the bark, causing discolouration and eventual death of the previous year’s leader. Consequently, the current-year leader above is starved of nutrients and water. It eventually wilts and degenerates into a characteristic ‘shepherd’s crook.’ This is the unmistakable signature of white pine weevil attack. The white, legless larvae within the leader reach 9 to 10 millimetres when fully grown. These larvae form a chamber of wood chips (chip cocoon) in the centre of the dead leader and pupate. By late summer, this leader is riddled with circular holes where mature weevils have emerged.

In subsequent years, damaged trees initiate many new shoots from the point where the leader was killed. Several of these may survive and continue to grow, resulting in a tree with multiple leaders. The legacy of repeated attacks on young white pine and other hosts can be seen several decades later in mature trees with crooked stems, multiple stems or leaders, and twisted tops.

Life cycle

White pine weevil has one generation per year. Eggs are laid in feeding pits just below the terminal bud cluster and plugged with macerated phloem. Hundreds of eggs may be laid in a single leader, making competition a significant factor in survival of larvae.

Following the hatch, larvae feed downward on the nutritious phloem where they are protected under the bark. As the larvae mature, their feeding tunnels girdle the leader, stopping the flow of nutrients through the terminal leader to new growth above. Pupal chambers made of strands of wood are formed in the pith of the leader. Following pupation, adults chew their way out of the leader and feed for several weeks before moving to the ground to overwinter. They emerge from overwintering sites the following spring and disperse to other trees, where they aggregate on terminal leaders to feed, mate, and oviposit.

Adult weevils may live up to four years. They produce only one new generation per year.

Damage

Attacks are most common on vigorously growing trees with leader diameters greater than 4 millimetres and overall tree heights of less than 6 metres. This preference for smaller trees means attack rates on most trees decline markedly after about 20 years. This makes white pine weevil a more significant pest in afforestation, reforestation, Christmas tree plantations, and tree nurseries.

White pine weevil kills at least 2 years of terminal leader growth in one season of attack. In small trees (<0.5 metres) the entire length of the stem may be mined in one year, causing tree death. Several new leaders will develop in the following years and many will be attacked. Trees rarely die from attacks, but there are negative consequences from multiple leaders on wood quality for forestry and shape for Christmas trees and ornamentals.

Prevention and management

Pest management strategies for a particular pest vary depending on several factors. These include:

• the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
• the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
• an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
• how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
• the value of the host(s) versus the costs of pest management approaches; and
• consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.

Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any pest.

Ecological conditions favouring attack and successful development of white pine weevil are manageable through the specific silvicultural practices of the previous century. These practices ensure white pine is regenerated under a shelter cover of overstory trees (commonly referred to as “shelterwood”), such as oak and/or mature white pine. Similarly, in the western range where white spruce regenerates under the protection of aspen (Populus), shelter from the latter trees keeps the understory cool and less favourable to weevil activity and limits the size of the host’s leader, making the leader less favourable for weevil oviposition. Once conifers susceptible to white pine weevil are well established, the shelterwood trees are cut to release the regenerating pine or spruce. The released trees then grow rapidly out of the susceptible size class. Small harvest blocks and selective harvesting also maintain at least partial shade, which may reduce the favourability of the habitat for white pine weevil. Large harvest blocks followed by planting of susceptible host trees in the open space (common procedures in modern commercial forestry practices) cause greater damage by this insect.

Mechanical methods such as clipping infested leaders and destroying the brood before it emerges in summer can reduce populations. These methods, however, are labour intensive and usually must be repeated over several consecutive years. This approach is often used in Christmas tree production and field-grown ornamental pines and spruces.

Considerable effort has gone into selecting less susceptible (or resistant) trees. Heritable, genetic variation in attributes that resist weevil attacks, such as rapid growth rates and density of defensive resin canals, have been identified but not widely exploited. Variation in resistance associated with site conditions such as adequate drainage and nutrients that enhance the vigour of young trees are likely a more practical silvicultural mitigation measure.

Biological controls have also been investigated. Lonchaea corticis Taylor, a predatory fly, is a common and effective natural enemy in natural populations but methods to enhance their populations for active management have not yet been developed.

The principal difficulty with pesticide treatments is that the adults are active in open, warm sites relatively early in spring and difficult to target with ground applications. Once larvae are feeding under the bark, they are protected from topical applications. Pesticides registered for use against white pine weevil under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered pesticides and product information for use against this insect. The application of any registered product should be based on population size and applied only when necessary and against the approved life stage. It is also recommended to consult a local tree care professional. Pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and follow all directions and precautions noted on the manufacturer’s label. In some jurisdictions and situations, only a licensed professional can apply pesticides. Consulting relevant local authorities to determine local regulations that are in place is recommended.

Selected references

Alfaro, R.I.; Borden, J.H.; Fraser, R.G.; Yanchuk. A. 1995. The white pine weevil in British Columbia: basis for an integrated pest management system. The Forestry Chronicle 71(1): 66–73. https://doi.org/10.5558/tfc71066-1  

Alfaro, R.I.; Borden, J.H.; King, J.N.; Tomlin, E.S.; McIntosh, R.L.; Bohlmann, J. 2002. Mechanisms of resistance in conifers against shoot infesting insects. The case of the white pine weevil Pissodes strobi (Peck) (Coleoptera: Curculionidae). Pages 105–130 in M.R. Wagner, K.M. Clancy, F. Lieutier, and T.D. Paine, editors. Mechanisms and deployment of resistance in trees to insects. Springer Dordrecht. Netherlands. 332 p.

King, J.N.; Alfaro, R.I.; Cartwright, C. 2004. Genetic resistance of Sitka spruce (Picea sitchensis) populations to the white pine weevil (Pissodes strobi): distribution of resistance. Forestry 77(4): 269–278. https://doi.org/10.1093/forestry/77.4.269 

Laffin, R.D.; Langor, D.W.; Sperling, F.A.H. 2004. Population structure and gene flow in the white pine weevil, Pissodes strobi (Coleoptera: Curculionidae). Annals of the Entomological Society of America 97(5): 949–956. https://doi.org/10.1603/0013-8746(2004)097[0949:PSAGFI]2.0.CO;2

Lavallée, R.; Archambault, L.; Morissette, J. 1996. Influence of drainage and edge vegetation on levels of attack and biological performance of the white pine weevil. Forest Ecology and Management 83(1–3): 133–144. https://doi.org/10.1016/0378-1127(95)03676-8

Lavallée, R.; Bonneau, G.; Coulombe, C. 1997.  Mechanical and biological control of the white pine weevil. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre. Sainte-Foy, Quebec. Laurentian Forestry Centre Information Leaflet LFC 28. 11 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/2029f926-b1b2-4a07-96fa-9a97f0263d09?fromSearchPage=true

Major, J.E.; Mosseler, A.; Barsi, D.C.; Clouthier, A.; Campbell, M. 2009. Impact of three silvicultural treatments on weevil incidence, growth, phenology, and branch-level dynamics of Pinus strobus from large and small populations. Canadian Journal of Forest Research 39(1): 12–25. https://doi.org/10.1139/X08-153

Nealis, V.G. 1998. Population dynamics of the white pine weevil, Pissodes strobi, infesting jack pine, Pinus banksiana, in Ontario, Canada. Ecological Entomology 23(3): 305–313.  https://doi.org/10.1046/j.1365-2311.1998.00136.x

Ostry, M.E.; Laflamme, G.; Katovich; Forest S.A. 2010. Silvicultural approaches for management of eastern white pine to minimize impacts of damaging agents. 2010. Forest Pathology 40(3–4): 332–346. https://doi.org/10.1111/j.1439-0329.2010.00661.x

Tomlin, E.S.; Borden J.H. 1996. Feeding responses of the white pine weevil, Pissodes strobi (Peck) (Coleoptera: Curculionidae), in relation to host resistance in British Columbia. The Canadian Entomologist 128(4): 539–549. https://doi.org/10.4039/Ent128539-4

Wallace, D.R.; Sullivan, C.R. 1985. The white pine weevil, Pissodes strobi (Coleoptera: Curculionidae): a review emphasizing behavior and development in relation to physical factors. Proceedings of the Entomological Society of Ontario, Supplement to Vol. 116: 39–62.

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Photos

Adult white pine weevil (dorsal view)

Thérèse Arcand

Adult white pine weevil near the exit hole of its pupal chamber

Thérèse Arcand

Larvae of white pine weevil that have been exposed within the terminal shoot of eastern white pine.

Thérèse Arcand

White pine weevil eggs that have been deposited by the female in a small feeding pit in the terminal shoot of Norway spruce.

Thérèse Arcand

Circular exit holes where white pine weevil adults have emerged on a terminal shoot of black spruce .

Thérèse Arcand

Holes chewed in the terminal shoot of Norway spruce by white pine weevil adults where they have both fed and laid eggs.

Thérèse Arcand

Typical appearance of dead terminal shoot of Norway spruce infested by white pine weevil.

Marc Bolduc

Typical appearance of dead terminal shoot of spruce infested by white pine weevil.

Marc Bolduc

Typical appearance of dead terminal shoot of eastern white pine infested by white pine weevil.

Jean-Pierre Bérubé

Adult white pine weevil (lateral view).

Thérèse Arcand

Typical appearance of dead terminal shoot of eastern white pine infested by white pine weevil.

Jean-Pierre Bérubé

White pine weevil pupa in its pupal cell in the terminal shoot of eastern white pine.

Thérèse Arcand