Jack pine budworm
- French common name: Tordeuse du pin gris
- Scientific name: Choristoneura pinus pinus Freeman
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Lepidoptera
- Family: Tortricidae
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Partial list of synonyms:
- Choristoneura fumiferana (Clemens)
General information and importance
Jack pine budworm is the most common and wide-spread pine-feeding budworm native to North America. For many years, it was referred to as the “pine form” of spruce budworm (Choristoneura fumiferana) because of its near identical appearance, life cycle, and overlapping geographic range with spruce budworm. Genetic analysis, however, has shown jack pine budworm to be more distinct from spruce budworm than are western spruce budworm (C. occidentalis) and two-year cycle spruce budworm (C. occidentalis biennis). An isolated and apparently distinct population of jack pine budworm in the northeastern United States is designated C. pinus maritima, but little is known of its status.
Outbreaks of jack pine budworm were historically more common in the Prairie provinces of Canada and American states bordering Lakes Michigan and Superior. Since the 1980s, however, outbreaks have become recurrent in northern Ontario and occasionally further east. At the same time, outbreaks west of the Great Lakes have diminished. Jack pine budworm outbreaks are different from those of other familiar budworms in that they last for only a few years in any one location and have highly variable return times.
Distribution and hosts
The geographic range of jack pine budworm is associated with that of its principal host, jack pine (Pinus banksiana). Both the tree and the budworm can be found in a broad band from central Alberta through the more southern boreal forest region, east to the Maritime provinces, and south to the United States, specifically the midwestern states adjacent to the Great Lakes.
Secondary hosts include red pine (P. resinosa), eastern white pine (P. strobus), and occasionally the introduced Scots (P. sylvestris) and mugo pine (P. mugo). Reports of jack pine budworm on spruce trees may be related to its similar appearance to spruce budworm. It could also be due to spill-over during outbreaks, as jack pine often occurs in stands mixed with black spruce.
Tree parts affected
Current-year buds, needles, and pollen cones
Symptoms and signs
Eggs are green and laid in two or three overlapping rows on needles. Just before hatch, the dark head of the developing larva can be seen in each fertile egg. Early-stage larvae have reddish brown heads and uniformly pale brown bodies. Final-stage larvae are 20 to 24 millimetres in length, with reddish brown heads and bodies distinctly marked with two rows of cream-coloured spots on each dorsal segment. Jack pine budworm are medium-sized moths with a wingspan of 18 to 24 millimetres, which is slightly smaller than spruce budworm. Wing colour is also similar to spruce budworm, with white and brown markings. One notable difference is a reddish, rather than smoky grey, base colour.
The first signs of damage in spring are less conspicuous than in other budworms. Small larvae of jack pine budworm do not mine needles. They feed within developing pollen cones (microsporangia). Strands of silk may be seen hanging from foliage as small budworms move around the canopy. As new shoots elongate, larvae chew needles off at their base. The excised needles become tangled in silk webbing, giving shoots an untidy appearance. As damaged needles dry in mid-summer, trees appear scorched red.
Top stripping of the sparsely foliated crowns of jack pine trees is observed frequently during outbreaks. Large, ‘wolf’ trees with multiple leaders are a legacy of old trees that have survived repeated damage to their leading shoots over several previous outbreaks.
Life cycle
Jack pine budworm has one generation per year. Eggs are laid on needles in masses of 30 to 60 eggs from late July to mid-August. Eggs hatch 1 to 2 weeks later. The newly hatched budworms do not feed. They move inwards from the foliage to the interior of the tree, settling in protected niches on the branches and trunk where they hibernate.
Larvae emerge in the spring between mid-May and mid-June, typically two to three weeks in advance of bud flush. Unlike spruce budworm, larvae of jack pine budworm are unable to mine old needles. Their survival during this critical period depends on availability of pollen cones on the host. Several small larvae will aggregate in a single cone. As current-year shoots become available, budworms construct a feeding shelter, begin feeding on the developing needles, and complete their growth in July. They often pupate within their feeding shelters.
Adult moths emerge within 2 weeks. Female moths emit a pheromone that attracts males to mate. Warm atmospheric conditions, typical of mid-summer in northern forests, favour increased moth activity at dusk. Moths follow convective air currents above the tree canopy where they may be transported many kilometres.
Outbreaks are most common in mature forests dominated by jack pine. These outbreaks can become synchronized across large areas. The intensity of defoliation is greatest in dense stands with closed canopies. The distinguishing factor of jack pine budworm outbreaks from outbreaks of other conifer-feeding budworms is their short duration and greater frequency. This is related to the reliance of jack pine budworm on pollen cones for survival in the spring. Jack pine produces pollen cones more frequently than most conifers, but pollen cone production is reduced following defoliation. Consequently, at first, jack pine budworm survival is favoured by the abundance of pollen cones. As jack pine budworm numbers increase and cause defoliation, pollen cone production decreases and becomes a negative feedback on survival. As populations decline, natural enemies, especially insect parasitoids, play a significant role in the collapse of outbreaks. The short duration of outbreaks means that most trees recover and become susceptible to a new infestation again within a few years.
The historic outbreak cycle in the Canadian Prairie provinces was around 10 years and associated with fire history. In the United States, outbreak cycles are more variable and related to soil and moisture conditions. Outbreaks since 1980 have occurred farther east in Canada. There is insufficient data to identify temporal patterns.
Damage
Outbreaks of jack pine budworm can affect hundreds of thousands of hectares of forests in a shifting mosaic of damage. Mortality of dominant trees is infrequent and distributed evenly across any one forest that was defoliated. Survey estimates of mortality of intermediate and suppressed trees are substantially greater. The estimates include natural thinning processes in these size classes and so surveys may inflate the effects of budworm damage. Secondary infections by root rot (Armillaria) also contribute to these mortality estimates. Top stripping is common but generally does not affect the merchantable portion of the tree. Radial growth can decline up to 50% with severe defoliation, but trees usually recover in a few years.
Damage to cones may occur in managed seed orchards. However, the naturally high propensity for jack pine to produce new cones reduces the significance of this damage.
The death of intermediate and suppressed trees and accumulation of dead needles on the forest floor following an outbreak contribute to the likelihood of wildfire. Jack pine is a fire-adapted species, growing on open, dry sites, and relying on fire for regeneration. These budworm-related changes may enhance forest renewal.
Prevention and management
Aerial application of insecticides to reduce damage is the most common intervention during extensive outbreaks. Forecasting populations with pheromone traps and estimates of egg mass densities are less accurate predictors of future damage by jack pine budworm compared to spruce budworm. Pheromones and insecticides are defined as pest control products and are regulated in Canada. Products registered for use against jack pine budworm under specific situations may change from year to year. Therefore, please search Health Canada’s Pesticide Product Information Database for currently registered products 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. Chemical pesticides may be toxic to humans, animals, birds, fish, and other beneficial insects. Apply registered products only as necessary and according to 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.
As most trees survive defoliation, accelerated or re-scheduled harvesting is often feasible, depending on the local timber supply and forest management objectives. Salvage harvesting can recover some commercial value where mortality has already occurred.
Hazard-rating systems indicate silvicultural approaches to reducing impacts. Older forests with low stocking rates and on poor sites are most susceptible to defoliation. Jack pine forests should be kept well-stocked and harvested on a shorter rotation.
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 for any particular pest.
Photos
Newly emerged jack pine budworm moth next to its empty pupal case attached to a pine shoot.
Thérèse Arcand
Jack pine budworm larva on a Scots pine shoot.
Thérèse Arcand
Jack pine budworm pupa tied with silk to pine needles. Note also the cast skin from the last moult near the pupa.
Thérèse Arcand
Adult jack pine budworm, pinned with wings spread.
Thérèse Arcand
Jack pine budworm egg mass on a jack pine needle.
Thérèse Arcand
Jack pine budworm egg masses on jack pine needles.
Thérèse Arcand
Jack pine budworm larva on a jack pine shoot.
Thérèse Arcand
Jack pine budworm larva on male flower-bearing jack pine shoot.
Thérèse Arcand
A dominant jack pine tree severely defoliated by jack pine budworm.
René Martineau
Jack pine stand moderately defoliated by jack pine budworm. Note that most defoliation has occurred in the upper crowns of infested trees.
René Martineau
Young jack pine stand moderately defoliated by jack pine budworm. Note that most defoliation has occurred in the upper crowns of the infested trees.
René Martineau
Selected references
Gross, H.L. 1992. Impact analysis for a jack pine budworm infestation in Ontario. Canadian Journal of Forest Research 22(6): 818–831. https://doi.org/10.1139/x92-111
Hall, R.J.; Volney, W.J.A.; Wang, Y. 1998. Using a geographic information system (GIS) to associate forest stand characteristics with top kill due to defoliation by the jack pine budworm. Canadian Journal of Forest Research 28(9): 1317–1327. https://doi.org/10.1139/x98-108
Hughes, J.S.; Fortin, M.-J.; Nealis, V.; Régnière J. 2014. Pollen cone production in jack pine: spatial and temporal patterns subject to natural disturbance by the jack pine budworm. Canadian Journal of Forest Research 44(3): 195–211. https://doi.org/10.1139/cjfr-2013-0089
MacQuarrie, C. 2020. Jack pine budworm. Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre. Sault Ste. Marie, Ontario. Frontline Express 86. 2 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/ec792437-bc1b-4073-821e-1a26920166fd?fromSearchPage=true
Nealis, V.G. 2016. Comparative ecology of conifer-feeding spruce budworms. The Canadian Entomologist 148 (S1): S33–S57. https://doi.org/10.4039/tce.2015.15
Nealis, V.G.; Magnussen, S.; Hopkin, A.A., 2003. A lagged, density-dependent relationship between jack pine budworm Choristoneura pinus pinus and its host tree Pinus banksiana. Ecological Entomology 28(2): 183–192. https://doi.org/10.1046/j.1365-2311.2003.00502.x
Volney, W.J.A, 1988. Analysis of historic jack pine budworm outbreaks in the Prairie provinces of Canada. Canadian Journal of Forest Research 18(9): 1152–1158. https://doi.org/10.1139/x88-177
Volney, W.J.A.; McCullough, D.G. 1994. Jack pine budworm population behavior in northwestern Wisconsin. Canadian Journal of Forest Research 24(3): 502–510. https://doi.org/10.1139/x94-067