Species Pristiphora geniculata - Mountain Ash Sawfly

Pristiphora (Pristiphora) geniculata (Hartig 1840)

native to Europe, adventive in NA; widespread in ne. US & Canada; "common east of the Mississippi River"(1)

First detected in Washington State in 2009, and now common throughout the Puget Sound region

Jun-Sep

Main host: Mountain-ash (Sorbus)

Overwinters as cocoon in the dirt. Two generations in the south, one in the north. First generation usually emerges in June and the second at the end of July.

Eggs are laid in slits cut around the edges of the leaflets and hatching occurs in 1 week. These larvae straddle the edge of the leaf and feed around the periphery. When disturbed they raise their abdomens in the form of an "S." Larvae of the 1st and 2nd instars are gregarious; the 4th and 5th instars feed singly. Feeding stops in 2-3 weeks and the larvae drop to the ground and spin cocoons in the duff and top soil. About 20% of these pupate and appear as 2nd generation adults in July.(2)

Looney, C., Smith, D. R., Collman, S. J., Langor, D. W., & Peterson, M. A. (2016). Sawflies (Hymenoptera, Symphyta) newly recorded from Washington State. Journal of Hymenoptera Research, 49, 129.

Fact sheets: Rosetta (2012)(3) | anon. (2011)(4) | Hanson & Walker (2002)(5) | anon. (2000)(6)