Redheaded pine sawfly
- French common name: Diprion de LeConte
- Other common names: Red-headed pine sawfly
- Scientific name: Neodiprion lecontei (Fitch)
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Diprionidae
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Partial list of synonyms:
- Diprion lecontei (Fitch)
- Lophyrus lecontei Fitch
General information and importance
Redheaded pine sawfly is native to eastern North America. Significant damage by the insect was infrequent until the 1930s. Damage increased following the extensive planting of pine trees in Canada and the United States. The sawfly then became one of the most destructive insects, attacking young plantations of hard pines (e.g., red pine [Pinus resinosa], Scots pine [P. sylvestris], and jack pine [P. banksiana]) in New Brunswick, Quebec, and Ontario. Discovery of a naturally occurring nucleopolyhedrovirus specific to redheaded pine sawfly led to one of the first successful biological control programs to produce and apply a naturally occurring pathogen against a forest insect pest.
The common name ‘sawfly’ refers to the female adult’s saw-like ovipositor, which is used to cut slits in the foliage of the host tree and deposit eggs. Adult sawflies resemble their winged bee and wasp relatives, with membranous wings but a broader “waist” between the thorax and abdomen.
Distribution and hosts
Redheaded pine sawfly occurs throughout eastern North America, from Ontario to Prince Edward Island in Canada, and to all states primarily east of the Great Plains in the United States, as far south as Florida. The principal hosts are most native and introduced hard pine species, many of which are cultivated commonly in plantations. In Canada, these are native red pine and jack pine, and introduced Scots pine. These species and other pines, such as shortleaf pine (P. echinata), loblolly pine (P. taeda), longleaf pine (P. palustris), slash pine (P. elliottii), Virginia pine (P. virginiana), and the introduced mugo pine (P. mugo), are the preferred host species of redheaded pine sawfly in the United States.
Tree parts affected
Redheaded pine sawfly is a defoliator, feeding openly on older foliage. It is capable of consuming all age classes of pine needles. If trees are completely stripped of foliage, sawflies may damage shoots where the bark is tender.
Symptoms and signs
Feeding 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 a pair of prolegs on six or more abdominal segments, while 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.
Translucent eggs appear as discoloured patches in a row on the edge of pine needles in late June. Newly hatched larvae are whitish, with a brown head. They soon become yellow to pale green. Small larvae eat the outer edges of pine needles, leaving the central portion, which dries to resemble straw. Mature larvae are about 25 millimetres long, pale to deep yellow, with a reddish-brown head. There are four to eight rows of black spots on each segment running lengthwise along the body. Older larvae completely defoliate shoots and sometimes entire trees. Adult redheaded pine sawflies are 5 to 10 millimetres long, with conspicuous, segmented antennae. Females are robust, with a red head and thorax, black abdomen, and serrated antennae. Males are entirely black, with plumose (feather-like) antennae.
As with many sawflies, redheaded pine sawfly larvae feed openly and gregariously on pine shoots. These colonies of larvae and the concentrated damage their feeding produces are conspicuous evidence of an infestation.
Life cycle
There is a single generation per year in Canada and as many as three in Florida, United States. In Canada, female adult redheaded pine sawflies lay translucent whitish eggs (1.8 by 0.6 millimetres) singly in slits they cut into a pine needle in late June and early July. Several eggs may be deposited in a line along a single needle. More than 100 eggs may be laid at a time by a single female sawfly. Unfertilized eggs become males. Larvae emerge in 2 to 3 weeks. Larvae feed gregariously, communicating with pheromones to maintain community structure. They prefer feeding sites on the more exposed, outer shoots of the tree. If threatened, larvae raise the front and rear portions of their bodies in a defensive posture and regurgitate a chemical to discourage predators. Feeding continues until late summer.
Once mature, larvae drop to the ground and spin a reddish brown, paper-like cocoon in the upper layer of soil. They do not pupate immediately because they enter a physiological dormancy (diapause) for the winter. They resume development and pupate the following spring. A portion of this overwintering population may remain in diapause for more than a year. A population of actively feeding sawflies may consist of more than one generation of individuals. Adults bite a circular hole in the end of the cocoon to escape, after which, they mate, and reproduce.
Damage
Trees less than 3 metres tall are particularly susceptible to redheaded pine sawfly. Even a relatively low density of sawflies can completely defoliate and kill small trees, especially in red pine and jack pine plantations. Moderate defoliation stunts growth and creates multiple leaders, reducing the value of the plantation.
Prevention and management
Redheaded pine sawfly only became significant pest with the extensive planting of pine in commercial plantations early in the 20th century. Exposed trees in nurseries and ornamental settings are at greatest risk. As a native insect, however, it has many natural enemies. These enemies often quickly respond to outbreaks and reduce damaging population levels. A naturally occurring nucleopolyhedrovirus was found in 1950 and was developed as the control agent, Lecontvirus. It is the only viral product used routinely in Canada and has been effective as a foliar treatment against this insect in small-scale commercial situations. When only a few colonies are present on small trees, insects can be picked off by hand and destroyed.
Promoting tree vigour and selecting favourable growing sites away from overstory trees to encourage rapid release of young pines has been recommended, although sawflies also favour open, exposed situations. Avoiding areas with marginal moisture and nutrient conditions is an important silvicultural component of plantation management for pines.
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 redheaded 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
Male adult redheaded pine sawfly at rest on a red pine needle (dorsal view). Males are entirely black, with plumose (feather-like) antennae.
Thérèse Arcand
Small larvae of redheaded pine sawfly eat the outer edges of pine needles, leaving the central portion, which dries to resemble straw.
Thérèse Arcand
A red pine shoot with most of its second-year needles eaten. A few redheaded pine sawfly larvae are feeding on needles in the lower part of the photo.
Thérèse Arcand
Female adult redheaded pine sawfly at rest on a red pine needle (dorsal view). Note the red head and thorax of the female.
Thérèse Arcand
Lateral (upper) and dorsal (lower) views of two mature larvae of redheaded pine sawfly on red pine needles.
Thérèse Arcand
Redheaded pine sawfly cocoons: the larger one contains a female; the smaller one contains a male.
Thérèse Arcand
Redheaded pine sawfly adults mating (dorsal view). The larger female is on the left and the smaller male is on the right.
Thérèse Arcand
Redheaded pine sawfly adults mating (lateral view). The larger female is on the left and the smaller male is on the right.
Thérèse Arcand
A colony of redheaded pine sawfly feeding gregariously on Scots pine needles.
Thérèse Arcand
A close-up of a colony of redheaded pine sawfly feeding gregariously on Scots pine needles.
Thérèse Arcand
A close-up of a colony of redheaded pine sawfly feeding gregariously on red pine needles.
Thérèse Arcand
A colony of redheaded pine sawfly feeding gregariously on needles of a red pine shoot.
Thérèse Arcand
Two young redheaded pine sawfly larvae on a red pine needle.
Thérèse Arcand
Close-up of redheaded pine sawfly eggs laid in a row in slits cut along edges of red pine needles.
Jean-Paul Laplante
Young red pine plantation where severe defoliation by redheaded pine sawfly has resulted in tree mortality.
Pierre Therrien
Redheaded pine sawfly eggs laid in a row in slits cut along edges of pine needles.
Jean-Paul Laplante
A young red pine killed as a result of redheaded pine sawfly defoliation.
Pierre Therrien
Red pine branch stripped of its second-year needles by redheaded pine sawfly larvae.
Pierre Duval
A colony of redheaded pine sawfly feeding gregariously on red pine needles.
Pierre Therrien
Young red pine defoliated by redheaded pine sawfly.
Claude Monnier
Selected references
Benjamin, D.M. 1955. The biology and ecology of the red-headed pine sawfly. US Department of Agriculture, Forest Service. Washington, D.C. Technical Bulletin No. 1118. 57 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
Cunningham, J.C.; de Groot, P.; Kaupp, W.J. 1986. A review of aerial spray trials with Lecontvirus for control of redheaded pine sawfly, Neodiprion lecontei (Hymenoptera: Diprionidae) in Ontario. Proceedings of the Entomological Society of Ontario 117: 65–72.
Flowers, R.W.; Costa, J.T. 2003. Larval communication and group foraging dynamics of red-headed pine sawfly, Neodiprion lecontei (Fitch) (Hymenoptera: Symphyta: Diprionidae). Annals of the Entomological Society of America 96(3): 336–343. https://doi.org/10.1603/0013-8746(2003)096[0336:LCAGFD]2.0.CO;2
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
Wilson, L.F.; Averill, R.D. 1978. Redheaded pine sawfly. United States Department of Agriculture, Forest Service. Washington, D.C. Forest Insect & Disease Leaflet 14.