European pine sawfly
- French common name: Diprion du pin sylvestre
- Other common names: Lesser pine sawfly
- Scientific name: Neodiprion sertifer (Geoffroy)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Diprionidae
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Partial list of synonyms:
- Diprion sertifer Geoffroy
- Lophyrus sertifer Geoffroy
- Tenthredo sertifer Geoffroy
General information and importance
European pine sawfly is an introduced insect in Canada. It is native to northern Eurasian forests. It was first discovered in North America in New Jersey, United States, in 1925. It was not identified as an introduced species, however, until 1937. By this time, it was already widely distributed leading to the belief that it was likely introduced much earlier. Difficulties in identifying this group of sawflies contributed to the oversight. European pine sawfly was found in southwestern Ontario in 1939. During the next three decades, it became established throughout southern Ontario and in localized areas in the Atlantic provinces. Recent introductions occurred in south coastal British Columbia. Damage has been greatest in pine plantations and on isolated ornamental and urban trees.
The common name ‘sawfly’ refers to the female adult’s saw-like ovipositor, which she uses to cut slits in the foliage of the host tree and deposit her eggs. Unfertilized eggs become males. Adult sawflies resemble their winged bee and wasp relatives with membranous wings. They differ with a broader “waist” between the thorax and abdomen.
Distribution and hosts
This sawfly is indigenous to northern Eurasia, from Europe to Korea and Japan. It was introduced to the northeastern United States and spread westward to the Great Lakes states, with localized populations as far west as Montana and south to Kentucky. European pine sawfly is present throughout southern Ontario, with scattered detections in plantations farther north and west. Localized populations also occur in Atlantic Canada, including the island of Newfoundland, and in south coastal British Columbia.
Principal hosts in North America are all age classes of most hard pines (2 or 3 needles per fascicle). Hosts include pine species introduced to North America, including Scots pine (Pinus sylvestris), Austrian pine (P. nigra), and mugho pine (P. mugo), as well as species native to Canada, including jack pine (P. banksiana), red pine (P. resinosa), pitch pine (P. rigida), lodgepole pine (P. contorta), and ponderosa pine (P. ponderosa). Occasional feeding damage has been observed on eastern white pine (P. strobus). Field evidence suggests European pine sawfly develops best on introduced Scots pine, its principal host in Eurasia.
Tree parts affected
The insect feeds preferentially on older needles of host trees.
Symptoms and signs
European pine sawfly larvae are superficially similar in appearance to the larvae of moths and butterflies (caterpillars). Both groups have three pairs of segmented legs on their thorax and a variable number of unsegmented prolegs, or fleshy leg-like protuberances, on the bottom of their abdominal segments. The difference is that sawfly larvae have either no prolegs or, more commonly, six or more pairs of prolegs on abdominal segments. Caterpillars have five or fewer pairs of prolegs. Significant variation and overlap in the appearance of related sawfly species makes identification challenging unless the characteristics of several life-stages can be observed.
Eggs are yellowish brown and embedded in regularly spaced slits cut along the needle. Larvae hatching from this cluster of eggs the following spring feed gregariously on portions of these needles, leaving characteristic dried, partially consumed needles. Young larvae are 3 to 4 millimetres in length, uniformly grey-green, with a shiny black head. As larvae grow, they feed in conspicuous colonies. They consume entire needles, leaving the needle sheaths. This results in dry, curled tufts as remnants on the twigs and branches. Current-year needles are not consumed unless populations are very high, giving damaged tree crowns a bottle-brush appearance. Mature larvae are 18 to 25 millimetres long. The head is black, and the body is greyish green, with several light and dark longitudinal stripes. There is a pair of black-spotted rings and prolegs on each of the eight abdominal segments. When larvae are disturbed, they will often assume a characteristic defensive pose, with their heads curled back over their bodies. The prepupal stage is brown to pinkish brown. Pupal cocoons are cylindrical and dark brown. Female adults are 7 to 11 millimetres long, with a brownish-reddish yellow head and body, and darker eyes and pronotum (area of thorax closest to head). The long, conspicuous antennae are dark and serrated in females, and plumose (feather-like) in males.
Life cycle
European pine sawfly has one generation per year. Eggs are laid in autumn and are embedded completely in regularly spaced slits cut along the length of a pine needle by the adult female. Development proceeds to the embryonic stage and is then suspended during winter. Moisture content of the host needle tissues appears critical at this stage and may determine which trees are most suitable for the sawfly. Development resumes the following spring. Egg hatch occurs in May depending on local, seasonal temperatures. Young larvae move to the tips of the needles in groups and begin eating the softest needle tissue while avoiding the central vascular bundles and any remaining eggs. Larvae from one cluster of eggs remain together throughout the feeding period. Mature larvae form cocoons on the tree or in the top layers of soil beneath the host tree from late June through July. Once the cocoon is formed, the sawfly larvae moult to a less mobile stage and enter physiological dormancy (diapause) for the remainder of the summer. In some cases, this dormant stage may be extended for another season. Development resumes in late summer when adults emerge from their cocoons, mate, and lay eggs.
Damage
European pine sawfly has become a minor pest in Canada, with reports of occasional local infestations. All age classes of host trees are susceptible, but damage is most severe in small pine trees in plantation or nursery settings, Christmas tree plantations, and ornamental plantings. Tree mortality is infrequent, but tree form may be compromised. Unless infestations are severe, most damage will occur to older foliage and current-year foliage will be retained. It is unusual for significant defoliation to occur several years in a row.
Prevention and management
Damaging outbreaks are less frequent than previously reported and most likely occur in localized settings, such as pine Christmas tree plantations, nurseries, and on ornamentals. In many cases, conspicuous colonies of feeding sawfly larvae can be removed by hand and destroyed on low numbers of smaller trees.
Despite being an introduced species, European pine sawfly is attacked by a diverse assemblage of native natural enemies, including larval and cocoon parasitoids and predacious insects, birds, and small mammals. Predation of cocoons in the soil by small mammals is considered a major factor in both the native and introduced ranges of European pine sawfly. A study of small-mammal predation of N. sertifer by a Canadian ecologist, C.S. Holling, is one of the most classic and frequently cited publications in animal ecology.
Several species of European parasitoids were introduced to Canada as biological control agents. The most successful was a parasitic wasp, Pleolophus basizonus. A nuclear polyhedrosis virus specific to European pine sawfly was imported from Europe and developed as a control agent. It has been effective at reducing high populations of the sawfly. It is not persistent in an area once populations decline. Introduction of natural enemies and further development of the virus ended in 1980, as damaging populations of European pine sawfly in Canada became infrequent.
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 European pine sawfly 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
Close-up of mature European pine sawfly larva (lateral view) on a jack pine needle.
Thérèse Arcand
European pine sawfly cocoons: the larger one contains a female; the smaller one contains a male.
Thérèse Arcand
European pine sawfly eggs laid in slits cut into Scots pine needles. Eggs are laid in the fall.
Carole Germain
Close-up of a colony European pine sawfly larvae feeding gregariously on pine needles. All needles have been chewed near to their base.
Thérèse Arcand
Multiple European pine sawfly cocoons on a pine twig.
Thérèse Arcand
Mugho pine shoot with second-year needles defoliated by European pine sawfly larvae.
Thérèse Arcand
A newly emerged male adult European pine sawfly next to its cocoon.
Thérèse Arcand
Mature European pine sawfly larvae viewed from three perspectives: ventral (left larva), dorsal (middle larva), and lateral (right larva).
Service canadien des Forêts
Characteristic dried, partially consumed needles resulting from feeding by first and second instar larvae of European pine sawfly. These needles are where eggs of the sawfly were laid the previous year.
Rayanne Lehman, Pennsylvania Department of Agriculture, www.forestryimages.org
Colony of European pine sawfly larvae feeding on the second-year needles of pine.
Jim Occi, BugPics, www.forestryimages.org
Female adult European pine sawfly at rest on a pine needle.
Louis-Michel Nageleisen, Département de la Santé des Forêts - France, www.forestryimages.org
Male adult European pine sawfly at rest on a pine needle.
Louis-Michel Nageleisen, Département de la Santé des Forêts - France, www.forestryimages.org
Mature European pine sawfly larva (lateral view) in a characteristic defensive posture on a defoliated Scots pine twig.
Louis-Michel Nageleisen, Département de la Santé des Forêts - France, www.forestryimages.org
European pine sawfly eggs laid in slits cut into a pine needle. Eggs are laid in the fall.
E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, www.forestryimages.org
Mature European pine sawfly larvae feeding gregariously on Scots pine needles.
Robert W. Duncan Centre de foresterie du Pacifique, Victoria (Colombie-Britannique) / Pacific Forestry Centre, Victoria, British Columbia
Selected references
Coppel, H.C.; Benjamin, D.M. 1965. Bionomics of the Nearctic pine-feeding diprionids. Annual Review of Entomology 10: 69–96. https://doi.org/10.1146/annurev.en.10.010165.000441
Duncan, R.W. 2006. Conifer defoliators of British Columbia. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre. Victoria, British Columbia. 359 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/0d752df6-d7a9-4d7d-b14d-9a35f1f36ef9?fromSearchPage=true
Griffiths, K.J. 1959. Observations on the European pine sawfly, Neodiprion sertifer (Geoff.), and its parasites in southern Ontario. The Canadian Entomologist 91(8): 501–512. https://doi.org/10.4039/Ent91501-8
Griffiths, K.J.; Cunningham, J.C.; Otvos, I.S. 1984. Neodiprion sertifer (Geoffroy), European pine sawfly (Hymenoptera: Diprionidae). Pages 331–340 in J.S. Kelleher and M.A. Hulme, editors. Biological control programmes against insects and weeds in Canada, 1969-1980. Commonwealth Agricultural Bureaux. Slough, England.
Holling, C.S. 1959. The components of predation as revealed by a study of small-mammal predation of the European pine sawfly. The Canadian Entomologist 91(5): 294–320. https://doi.org/10.4039/Ent91293-5
Lyons, L.A. 1964. European pine sawfly, Neodiprion sertifer (Geoff.) (Hymenoptera: Diprionidae). A review with emphasis on studies in Ontario. Proceedings of the Entomological Society of Ontario 94: 5–37.
MacQuarrie, C.J.K.; Lyons, D.B.; Seehausen, M.L.; Smith, S.S. 2016. A history of biological control in Canadian forests, 1882–2014. The Canadian Entomologist 148(Supplement S1): S239–S269. https://doi.org/10.4039/tce.2015.66
Ross, H.H. 1955. The taxonomy and evolution of the sawfly genus Neodiprion. Forest Science 1(3): 196–209.
Wallace, D.R.; Cunningham, J.C. 1995. Diprionid sawflies. Pages 193–232 in J.A. Armstrong and W.G.H. Ives, editors. Forest insect pests in Canada. Natural Resources Canada, Canadian Forest Service, Science and Sustainable Development Directorate. Ottawa, Ontario. https://publications.gc.ca/site/eng/9.889231/publication.html