Swaine jack pine sawfly

Swaine jack pine sawfly - Colony of young larvae on a jack pine shoot
  • Latin name: Neodiprion swainei Middleton
  • French name: Diprion de Swaine
  • Order: Hymenoptera
  • Family: Diprionidae


Nova Scotia, New Brunswick, Prince Edward Island, Quebec, Ontario, Manitoba, Alberta



Damage, symptoms and biology

Swaine jack pine sawfly activity can be identified in June or July from the presence of egg-laying scars on the current year's needles and needles with chewed margins. Later in the season, empty sheaths, partial or complete defoliation and cocoons at the base of trees may also be seen, indicating that this insect is at work.

The Swaine jack pine sawfly usually attacks old stands. The trees may survive if the the insect only feeds on the old needles. However, complete defoliation generally leads to tree mortality as early as the following year.

The female sawfly typically deposits one egg at the same height on both of the needles in a bundle, on the current year's shoot. Females deposit all their eggs on the same annual shoot. After hatching, the larvae congregate in colonies and begin to feed on old needles in groups of two or three per needle.

The yellowish young larvae eat the outer portion of the needles, leaving only a thin filament. Older larvae, which have a yellowish-green body bearing two dark dorsal lines, eat the entire needle and devour all the old foliage. During heavy infestations, they also attack the current year's needles.

After completing their development, the larvae fall to the ground and spin a cocoon in the litter in which they overwinter. Pupation occurs in the spring and the adults emerge in June. Part of the population remains in diapause for a longer period.

Life cycle (East of the Rockies)

Life cycle (East of the Rockies)
Stage/Month J F M A M J J A S O N D

Other information

Native to North America, the Swaine jack pine sawfly is considered the most serious defoliator of jack pine and has been recorded annually since 1936. Since then, this insect has gained notoriety for the destruction of huge stands of jack pine in Quebec and Ontario. Its distribution range covers essentially the same area as jack pine.

To protect isolated trees, it is advisable to cut off shoots bearing eggs before eclosion. However, if larvae are already present, the best approach is to shake the tree and then destroy all the larvae that fall to the ground.

Canadian Forest Service Publications

Swaine jack pine sawfly

Diet and feeding behaviour

  • Phyllophagous : Feeds on the leaves of plants.
    • Free-living defoliator: Feeds on and moves about freely on foliage.
Information on host(s)

Main host(s)

Jack pine

  • Swaine jack pine sawfly Lateral view of the adult female (length: 6-8 mm)
  • Swaine jack pine sawfly Three larvae feeding on the same jack pine needle
  • Swaine jack pine sawfly Close-up of egg-laying scars
  • Swaine jack pine sawfly Colony of young larvae on a jack pine shoot
  • Swaine jack pine sawfly Colony of young larvae on a jack pine shoot
  • Swaine jack pine sawfly Section of a severely defoliated young jack pine
  • Swaine jack pine sawfly Mature jack pine forest destroyed after a severe attack
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