Species Diprion similis - Introduced Pine Sawfly

Diprion simile (misspelling)

Diprion similis (Hartig 1834)

adventive from Europe; ne. US (ME-MN to NC-TN) (map) + WA; in Canada, NF-MB & BC

Pine forests

Adults can be found throughout the season, from first emergence in mid-spring to pupation in mid-fall (in favorable weather they may stay active even longer). Late-emergers and two generations mean all stages of development can be found together at the same time.

hosts: pines (Pinus); 5-needled pines (Subg. Strobus) are preferred, but others may be infested as well

Male | Female

Adults emerge as early as April, depending on the climate, and mate (Females that fail to mate can still lay eggs, which hatch to produce males). The females make slits in needles with their ovipositors to lay their eggs- about 10 per needle. When they first emerge, the larvae feed in groups, but spread out as they get older.

Larva:

There are often two generations, with the first spinning cocoons in early July, emerging in early August, and laying eggs which hatch into the second generation. The second generation generally spins cocoons in September in the litter under the trees.

Most go into diapause in a pre-pupal state until spring, then pupate. Some may not emerge with the others, remaining in diapause until later in the season, or even for 1-3 years.

Empty cocoon:

With exit hole of a chalcid wasp:

First reported in our area: CT 1914

Although a serious pest at times, it normally stunts rather than kills its hosts. It can be a more serious problem with young trees and in cases such as Christmas trees where appearance is important. It has natural enemies and diseases, so large outbreaks are only intermittently seen.

The introduced parasite, Monodontomerus dentipes, has a 75% effective record in NJ.(1)

Fact sheets: anon. (2011)(2) | Wilson (1966)(3)