Pine shoot beetle
- French common name: Grand hylésine des pins
- Other common names: Common pine shoot beetle, larger European pine shoot beetle
- Scientific name: Tomicus piniperda (L.)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Curculionidae
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Partial list of synonyms:
- Blastophagus piniperda Eichoff
- Myelophilus piniperda Eichoff
General information and importance
Pine shoot beetle is one of the most widely distributed forest insects and common pest of pines from western Europe to eastern China and Japan. Reports across this range reveal considerable variation in its habits, seasonality, and nature of the damage. In North America, it was first discovered in the United States in Ohio in 1992, likely introduced in wood packing material several years previously. It was found soon after in several other states surrounding the Great Lakes and in southern Ontario and Quebec. It has since spread throughout most of the eastern forests of the United States but not as widely in eastern Canada. Pine shoot beetle is considered a primary pest in Christmas tree plantations where the adults destroy the living shoots of susceptible trees. They are also secondary pests as they colonize weakened and recently felled trees in which they raise their brood.
Distribution and hosts
Pine shoot beetle is widely distributed and common across its native range from the Atlantic coast of Europe to Japan and Hong Kong in Asia, and from the timberline in Fennoscandia to north Africa. It has been introduced to North America and is currently found in most northeastern United States from Wisconsin to Maine and south to Missouri and Virginia. In Canada, pine shoot beetle is established in southern Ontario and Quebec.
The beetle attacks many pine (Pinus) species in its native range but Scots pine (P. sylvestris) appears to be the principal host in Europe and preferred over native pines in North America. Some North American pine species planted in Europe have been attacked including lodgepole pine (P. contorta) and Monterey pine (P. radiata). In China, Yunnan pine (P. yunnanensis) plantations are particularly susceptible. In North America, most pines appear to be suitable hosts for completion of the life cycle and for shoot feeding by adult beetles. However, the female adult seems more selective about where she lays her eggs, choosing some pine species such as jack pine (P. banksiana) only when there is not a preferred choice such as Scots pine or freshly fallen trees available.
Tree parts affected
Developing shoots (branches). Adult pine shoot beetles bore into the living shoots of host pines causing them to wilt and break off. Brood galleries are excavated by adults under tree bark, often introducing blue-stain fungi, which infect the trees’ vascular systems. Larvae excavate feeding galleries in phloem tissue beneath the bark compromising translocation of water and nutrients, leading to branch dieback.
Symptoms and signs
Pine shoot beetle adults mine current shoots of healthy pine trees throughout the summer and autumn, leaving resin tubes at the entry point near the base of the shoot. Damaged shoots turn yellow-red and bend over. They eventually fall off the tree and accumulate on the ground. Removal of entire shoots by adults causes a noticeable thinning of the tree’s crown, especially at the top.
Successful excavation of brood galleries in felled or weakened trees is indicated by brown and white wood dust in bark crevices near the point of entry. Peeling back bark reveals longitudinal egg galleries along the wood grain; therefore, they are found vertically on standing trees and horizontally on fallen trees. Blue-stain fungi may be introduced by the beetle resulting in characteristic staining under the bark. Larvae are legless, curved grubs with a white body and brown head. Feeding larvae make winding galleries perpendicular to the egg gallery and each of these terminate in a pupal cell under the bark. Mature larvae are 4 to 5 millimetres in length. Pupae resemble adults in form but are white. Adults exit by chewing their way out through the bark, leaving clusters of round holes, each about 1.5 millimetres in diameter. Adults are 3 to 5 millimetres in length, light brown upon emergence, turning dark brown. Standing trees used for brood show significant dieback of limbs and eventual death as the vascular system is progressively damaged.
Life cycle
Pine shoot beetle completes one generation per year. Adults emerge from their overwintering sites under the outer bark on the lower stems of pine trees once spring temperatures are greater than 10°C. They are one of the earliest bark beetles to fly in the spring in North America. Adults are strong fliers and can move considerable distances in search of new host trees, which they locate by detecting host odours (plant volatiles). Adults may feed briefly on foliage but soon colonize freshly cut stumps, logs, and stressed, living trees. The beetles are monogamous, both sexes excavating brood galleries under the bark. Females lay eggs singly on either side of the gallery while the male adult removes frass. When egg laying is complete, the adults withdraw from the gallery. They may resume feeding on shoots in preparation for establishing additional new broods.
Larvae feed through the phloem in winding, separate galleries 2.5 to 10.0 centimetres long and perpendicular to the egg galleries. They complete larval development in late May or June and pupate at the end of the feeding gallery. In July, new adults emerge through individual exit holes, which they chew through the bark. Adults then fly to living trees where they begin maturation feeding in current pine shoots, burrowing through the middle of the shoot pith. Each adult may destroy as many as six healthy shoots during this maturation feeding. Adults exit these shoots following the first subfreezing temperatures in late autumn and move down the tree to overwintering sites under the bark at the base of the tree. Preferred overwintering locations are just above the duff layer where they are protected by snow cover. However, overwintering beetles may be found on tree trunks up to 0.5 metres above the soil line when beetle populations are more abundant. In warmer climates, adults may remain in the shoots for the winter, although this is rare.
Damage
Early fears that pine shoot beetle would invade natural pine forests in North America have not come to pass. For the most part, damage has been restricted to stressed Scots pine and native jack pine planted on poor sites. The most significant economic damage is caused by adult pine shoot beetles mining fresh shoots of trees. Damaged shoots turn yellow and are deformed, eventually breaking off, affecting growth and appearance, the latter of which is of importance in nurseries and Christmas tree plantations. Secondary damage is caused by adults colonizing stressed and recently fallen trees and establishing a brood beneath the bark. Feeding larvae construct galleries in phloem tissue beneath the bark causing branch dieback in living trees and eventual tree mortality.
Prevention and management
The clear association of pine shoot beetle with freshly felled trees, stumps, and stressed trees growing on poor sites provides clear strategies for prevention and management. Thinning out non-vigorous trees, replacing non-native species such as Scots pine, cutting stumps at ground level, and removing windfall are all silvicultural practices aimed at sanitizing stands and preventing increases in populations of pine shoot beetle. Population levels can be assessed with monitoring tools such as baited traps, which capture flying adult beetles and “bait logs” (freshly cut bolts of pine placed out early in the spring prior to first adult flight before temperatures reach 10°C) to focus colonization of pine shoot beetle. These bait logs provide an indication of local pest densities and infested bolts can be chipped or burned to destroy broods before emergence.
Following discovery of pine shoot beetle in the 1990s, regulatory (quarantine) policies were introduced by both Canadian and American government agencies. The objective was to reduce inadvertent movement of pine shoot beetle, especially via the Christmas tree market. However, these regulations have now been lifted given the apparent low risk of pine shoot beetle entering native pine forests and the argument that the costs associated with regulation outweigh the benefits of any delayed future damage that might result.
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 particular pest.
Pesticides registered for use against pine shoot beetle 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.
Photos
Damage
Gyorgy Csoka, Hungary Forest Research Institute, www.forestryimages.org
Beat Forster, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), www.forestryimages.org
Lateral view
Maja Jurc, University of Ljubljana, www.forestryimages.org
Dorsal view
Pest and Diseases Image Library, www.forestryimages.org
Lateral view lateral view; Bohemia C., Stark & Bolestav, 22 May 1994, M. Knizek & det M. Knizek
Pest and Diseases Image Library, www.forestryimages.org
Selected references
Bogdanski, B.E.C.; Corbett, L.; Dyk, A.; Grypma, D. 2018. Pine shoot beetle, Tomicus piniperda (Linnaeus): analysis of regulatory options for Canada. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Information Report BC-X-443. 26 p.
CABI Digital Library. 2021. Tomicus piniperda (common pine shoot beetle). CABI Compendium. Datasheet 54154. https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium [Accessed June 2024]
Haack, R.A.; Lawrence, R.K.; Heaton, G.C. 2000. Seasonal shoot-feeding by Tomicus piniperda (Coleoptera: Scolytidae) in Michigan. The Great Lakes Entomologist 33(1): 1–8. https://doi.org/10.22543/0090-0222.2009
Haack, R.A.; Poland, T.M. 2001. Evolving management strategies for a recently discovered exotic forest pest: the pine shoot beetle, Tomicus piniperda (Coleoptera). Biological Invasions 3: 307–322. https://doi.org/10.1023/A:1015298114837
Hausner, G.; Iranpour, M.; Kim, J.-J.; Breuil, C.; Davis, C.N.; Gibb, E.A.; Reid, J.; Loewen, P.C.; Hopkin, A.A. 2005. Fungi vectored by the introduced bark beetle Tomicus piniperda in Ontario, Canada, and comments on the taxonomy of Leptographium lundbergii, Leptographium terebrantis, Leptographium truncatum, and Leptographium wingfieldii. Canadian Journal of Botany 83(10): 1222–1237. https://doi.org/10.1139/b05-095
Humphreys, N.; Allen, E. 1998. The pine shoot beetle. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. Exotic Forest Pest Advisory 2. 4 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/ac22a6e1-4355-4064-bd0c-8ccaafd7a1b4?fromSearchPage=true
Långström, B. 1983. Life cycles and shoot-feeding of the pine shoot beetles. Swedish University of Agricultural Sciences, Faculty of Forestry. Uppsala, Sweden. Studia Forestalia Suecica 163. 29 p. https://core.ac.uk/download/pdf/11697170.pdf [Accessed September 2024]
Långström, B.; Lisha, L.; Hongpin, L.; Peng, C.; Haoran, L.; Hellqvist, C.; Lieutier, F. 2002. Shoot feeding ecology of Tomicus piniperda and T. minor (Col., Scolytidae) in southern China. Journal of Applied Entomology 126(7–8): 333–342. https://doi.org/10.1046/j.1439-0418.2002.00651.x
Morgan, R.E.; de Groot, P.; Smith, S.M. 2004. Susceptibility of pine plantations to attack by the pine shoot beetle (Tomicus piniperda) in southern Ontario. Canadian Journal of Forest Research 34(12): 2528–2540. https://doi.org/10.1139/x04-135
Petrice, T.R.; Haack, R.A.; Poland, T.M. 2002. Selection of overwintering sites by Tomicus piniperda (Coleoptera: Scolytidae) during fall shoot departure. Journal of Entomological Science 37(1): 48–59. https://doi.org/10.18474/0749-8004-37.1.48
Poland, T.M.; de Groot, P.; Burke, S.; Wakarchuk, D.; Haack, R.A.; Nott, R.; Scarr, T.A. 2003. Development of an improved attractive lure for the pine shoot beetle, Tomicus piniperda (Coleoptera: Scolytidae). Agricultural and Forest Entomology 5(4): 293–300. https://doi.org/10.1046/j.1461-9563.2003.00191.x
Siegert, N.W.; McCullough, D.G. 2001. Preference of Tomicus piniperda (Coleoptera: Scolytidae) parent adults and shoot-feeding progeny adults for three pine species. The Canadian Entomologist 133(3): 343–353. https://doi.org/10.4039/Ent133343-3
Ye, H.; Haack, R.A.; Petrice, T.R. 2002. Tomicus piniperda (Coleoptera: Scolytidae) within and between tree movement when migrating to overwintering sites. The Great Lakes Entomologist 35(2):183–192. https://www.nrs.fs.usda.gov/pubs/jrnl/2002/nc_2002_hui_001.pdf [Accessed September 2024]