(Diprion similis)  

Mature Larvae of the Introduced Pine Sawfly – Steven Katovich, USDA Forest Service

from PaBIA/Ojibway Yearbook 2015 pg. 98-99

written by Shelagh Grant, Chair of Forest and Wildlife

Surveys conducted by the Ontario Forest Health Monitoring Program indicated that the introduced pine sawfly was remaining at low levels in the Georgian Bay area.  Hence I presume that recent outbreaks on our islands were considered isolated events. Although it was reported that they rarely kill a tree, this does not appear to be the case on our outer islands and adjacent mainland shoreline, where the damage they can inflict is considerable unless checked.  There appear to be other types of sawflies found in our area, such as the white pine sawfly (Neodiprion pinetum), with similar life cycles and manifestation that respond to the same control methods. The major differences relate to the colouring of the adult larvae.

Defoliated Tree by a Pine Sawfly Infestation – John Ghent, USDA Forest Service

This is another imported pest, reportedly from Holland, which is now well established in eastern and central United States and Canada, but only first recorded in Ontario in 1931. The spread of the pest apparently was not rapid, but in the early 1990s the introduced pine sawflies had reached Georgian Bay, and causing mortality of white pines.  Light to moderate defoliation was observed in the Township of the Archipelago in 2000, with pockets of severe defoliation seen along Highway 69 near Pointe au Baril.  Although this pest favours the white pine of all ages, it will attack other pines. Unfortunately this particular pine sawfly is two generational, initially feeding in late May to early June and a second batch from late July through to early September.  The first generation feed only on old needles but the second generation feeds on both new and old, thus capable of major defoliation.

Sawfly Cocoon Attached to a Branch – G. Csoka, Hungary Forest Research Institute

The young larvae are pale greenish yellow with shiny black heads.  Hatching in May or early June, they initially appear in masses, feeding on tender portions of the needles. They later disperse and spread throughout a tree, devouring needles in their entirety.  The older larvae develop double stripes down their back along with many yellow, black and white spots on a dark grey background. By mid-July, they will spin dark brown cocoons that are cylindrical with tough walls.

Masses of young Pine Sawfly Larvae on Pine Branch – Steven Katovich USDA Forest Service

The emerging female sawfly will lay its eggs in slits cut into the needles, made by a saw-like structure at the tip of the abdomen – hence its name.  The second-generation larvae emerge between late July and late August, to begin another cycle.  They are usually more numerous and have been known to completely defoliate a tree since they feast on both the old and new needles. The second generation will spend the winter in their cocoons.

For effective control, it is important to destroy the first generation in its early stages. If still confined to a single branch, this can be pruned and burned.  Spot spraying masses of young larvae is also effective, using registered pesticides such as Malathion which is approved for use by Township of the Archipelago’s By-law No. 03-2.1, article 3 (h).  Read the label carefully and avoid letting mist or spray reach the water. The TOA By-Law is available in its entirety on the township’s website under Residents/By-laws/Fertilizers. Note that Bacillus thuringiensis (B.t.) is not effective on pine sawflies.

The introduced pine sawfly is one pest that does not require drought and stressed trees to thrive.  Although apparently less of a concern compared to several years ago, last August we observed the larvae in relatively large numbers on our island. We will be monitoring our trees closely next spring for any signs of infestation and deal with it accordingly.

from PaBIA/Ojibway Yearbook 2015 pg. 98-99

These additional photos were taken in Pointe au Baril this week (Sept 2015).

Look closely to see the larvae in each photo.