Red pine sawfly
- French common name: Diprion du pin rouge
- Other common names: Red-pine sawfly, black-headed jack-pine sawfly
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Scientific names:
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Neodiprion nanulus
Schedl
- Neodiprion nanulus contortae
- Neodiprion nanulus nanulus
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Neodiprion nanulus
Schedl
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Diprionidae
General information and importance
The red pine sawfly is native to North America. Two subspecies are recognized, Neodiprion nanulus nanulus, east of the Rocky Mountains, and Neodiprion nanulus contortae, in and west of the Rocky Mountains. Both subspecies feed on hard pines (2- and 3-needle pines) and are similar in their appearance and life history. Their main distinction is that they predominantly occur on different sides of the Rocky Mountains and are associated with the different hard-pine species that characterize these respective forest ecozones. For example, N. n. nanulus occurs to the east of the mountains on jack pine (Pinus banksiana). N. n. contortae occurs in the interior montane and coastal forests of British Columbia, west of the mountains on lodgepole pine (P. contorta var. latifolia).
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. 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
Neodiprion n. nanulus occurs in Canada, east of the Rocky Mountains from northeastern British Columbia east to Nova Scotia and Prince Edward Island. In the United States, it occurs from Wisconsin to southern Illinois and east to the Atlantic states as far south as Pennsylvania. In its American range, it feeds on a greater variety of pines, including red pine (P. resinosa), jack pine, pitch pine (P. rigida) and, to a lesser extent, shortleaf pine (P. echinata) and introduced Scots pine (P. sylvestris).
Neodiprion n. contortae occurs in the Rocky Mountains in western Alberta and into central British Columbia, south through the high-elevation forests to Montana and Idaho. It is common in cool Pacific coastal forests from Oregon, north through British Columbia. It has recently been reported for the first time in the coastal forests of southeast Alaska. In interior forests, it feeds on lodgepole pine and ponderosa pine (P. ponderosa). On the coast, it also feeds on shore pine (P. contorta var. contorta).
Tree parts affected
Older needles (one-year or older).
Symptoms and signs
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 (fleshy leg-like protuberances) on the bottom of their abdominal segments. Sawfly larvae either have no prolegs or, more commonly, six or more pairs on their 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.
In the fall, eggs may appear as swellings on the edge of needles. Larvae hatch in May and feed in colonies, moving from shoot to shoot as all older needles are consumed. Mature larvae are up to 21 millimetres long. The head is uniformly brown to black. The body is green to yellowish green, with a yellowish-green stripe along the middle of the back (middorsal), a broad green stripe on the upper side (subdorsal), and a series of paler green-grey stripes located more ventrally. Pine trees heavily damaged by sawflies may have all old needles removed, with only current-year growth surviving at the ends of the shoots.
Life cycle
The female adult sawflies of both subspecies lay their eggs in slits cut along the margins of needles of their pine hosts in the fall. Unfertilized eggs become males. As many as 10 eggs may be laid per needle in pines with short needles such as jack or lodgepole pine. More than 10 eggs per needle can be laid in pine hosts with longer needles such as red pine and ponderosa pine. The insect overwinters in the egg stage. Eggs hatch in the spring and the sawfly larvae feed in colonies on 1-year or older needles. Once the old needles of the entire shoot are consumed, colonies migrate to a new shoot to continue feeding. Female sawfly larvae complete five instars (feeding stages) and male larvae complete four. Mature larvae spin cocoons in the soil beneath the trees in early July and enter physiological dormancy (diapause) for the rest of the summer. A variable proportion may spend 2 or more years in this dormant state. Most adults emerge in September to October to mate and lay eggs. Several species of natural enemies have been recorded attacking larval and cocoon stages.
Damage
Damaging outbreaks mostly occur in plantations and pole-sized trees. Mature trees may also be attacked, especially in isolated or ornamental situations. The sawflies consume old needles unless populations are very high, so trees typically retain current-year growth. Tree mortality is uncommon even when all old needles are consumed, unless outbreaks last for more than 2 years. Neodiprion n. nanulus infrequently causes significant defoliation. However, Neodiprion n. contortae occasionally causes damage in interior and coastal forests in British Columbia. The latter subspecies has also been reported for recently causing significant defoliation in southeast Alaska. Tree mortality caused by either subspecies of sawfly is uncommon.
Prevention and management
Sawfly outbreaks on ornamental trees and in plantations are unsightly and retard growth for the period of defoliation. However, affected trees usually recover. The sawflies feed in conspicuous colonies and can be handpicked off smaller, high-value trees.
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 red 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
Larvae of red pine sawfly (N. n. nanulus) feeding gregariously on jack pine needles.
Jean-Paul Laplante
Red pine sawfly cocoons: the larger one contains a female; the smaller one contains a male.
Thérèse Arcand
Male adult red pine sawfly (N. n. nanulus) at rest on jack pine needles (dorsal view). Males are entirely black, with plumose (feather-like) antennae.
Thérèse Arcand
Female adult red pine sawfly (N. n. nanulus) at rest on jack pine needles (dorsal view). Females are larger than males and are more brown in colour.
Thérèse Arcand
Larva of red pine sawfly (N. n. contortae) on a red pine needle.
Thérèse Arcand
Larvae of red pine sawfly (N. n. nanulus) feeding gregariously on jack pine needles.
Robert W. Duncan Centre de foresterie du Pacifique, Victoria (Colombie-Britannique) / Pacific Forestry Centre, Victoria, British Columbia
Larvae of red pine sawfly (N. n. nanulus) feeding gregariously on jack pine needles.
Robert W. Duncan Centre de foresterie du Pacifique, Victoria (Colombie-Britannique) / Pacific Forestry Centre, Victoria, British Columbia
Larvae of red pine sawfly (N. n. nanulus) feeding gregariously on jack pine needles.
Robert W. Duncan Centre de foresterie du Pacifique, Victoria (Colombie-Britannique) / Pacific Forestry Centre, Victoria, British Columbia
Selected references
Ciesla, W.M.; Smith, D.R. 2011. Diprionid sawflies on lodgepole and ponderosa pines. United States Department of Agriculture, Forest Service, Pacific Northwest Region (R6). Portland, Oregon. Forest Insect & Disease Leaflet 179. 12 p.
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
Dahlsten, D.L. 1966. Some biological attributes of sawflies in the Neodiprion fulviceps complex in a brushfield pine plantation. The Canadian Entomologist 98(10): 1055–1083. https://doi.org/10.4039/Ent981055-10
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
Graham, E.; Mulvey, R. 2013. A new state record, Neodiprion nanulus contortae Ross collected from shore pine in southeast Alaska. Newsletter of the Alaskan Entomological Society 6: 1–3.
Ross, H.H. 1955. The taxonomy and evolution of the sawfly genus Neodiprion. Forest Science 1(3): 196–209.
Underwood, G.R. 1967. Parasites of the red-pine sawfly, Neodiprion nanulus nanulus (Hymenoptera: Diprionidae), in New Brunswick. The Canadian Entomologist 99(10): 1114–1116. https://doi.org/10.4039/Ent991114-10
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