The Diprionidae are known as the conifer sawflies, though they are not the only family to use conifer trees as hosts (others include Siricidae, Pamphiliidae, Xyelidae, and some genera of Tenthredinidae). Many are destructive pests as larvae, and so their biology has been more extensively studied than some other sawfly groups. Diprionids have stout bodies and distinctive antennal characteristics that make adults easy to recognize (Furniss and Carolin 1977).
Gilpinia is an Old World genus of which two species are introduced and established in North America. Larvae feed on spruce trees. Gilpinia hercyniae is well-known in North America and in Europe as an occasional pest (Jeger et al. 2017).
There are 37 described species worldwide, restricted to the Northern Hemisphere. Two species are introduced in North America (Taeger et al. 2010).
A preliminary key to North American species of Gilpinia is included in Reeks 1941.
Diprionidae are most easily recognized by the distinctive antennae of both sexes, but also are characterized by small, stout bodies. Gilpinia can be separated from other genera in the family by the large cenchri, small mesoscutellum, and the anterior margin of the mesoscutellum (Smith 1971b, Goulet 1992).
The two species that occur in North America were introduced from Europe (USDA 1985).
Gilpinia frutetorum larvae feed on several species of pine, with preference for Pinus resinosa (red pine) and Pinus sylvestris (Scots pine), and G. hercyniae larvae feed on spruce, with preference for Picea glauca (white spruce). Gilpinia hercyniae is also known to feed on Picea mariana (black spruce), Picea abies (Norway spruce), and Picea rubens (red spruce) (Reeks and Barter 1951, Van Driesche et al. 2013).
Gilpinia females oviposit into slits cut longitudinally along the needle. Emerged larvae are solitary feeders, progressing from the tip of the needle to the base. Larvae prefer to feed on older needles and only feed upon new growth after the majority of the old growth has been consumed. At maturity, the larva falls to the ground and builds a cocoon in the leaf litter. Depending on the generation, the prepupa may overwinter in the cocoon before pupating. Gilpinia hercyniae has 1–3 generations per year, and one female can lay up to 65 eggs (USDA 1985, Van Driesche et al. 2013, Jeger et al. 2017).
Gilpinia hercyniae was historically a pest of spruce due to periodic population outbreak events. A G. hycerniae outbreak in Quebec between 1932 and 1935 defoliated about 3.8 million acres. The economic impact was significant, especially since the species prefers mature trees. Populations are now controlled in North America by an introduced virus (Reeks and Barter 1951, Goulet 1981, USDA 1985, Van Driesche et al. 2013).
World: The species of Gilpinia are found throughout forested regions of Europe and central and eastern Asia (Jeger et al. 2017).
North America: The two species of introduced Gilpinia were both first discovered in the Northeast in the early twentieth century and have since become widespread. Their range includes Newfoundland, Quebec, and Manitoba in the north, south through New England and the northern Midwest, to New Jersey and Pennsylvania in the south (Van Driesche et al. 2013). Gilpinia hercyniae is also recorded from Washington State (Looney et al. 2016).
Map data from: GBIF.org (26 June 2019) GBIF Occurrence Download Gilpinia
Details about data used for maps can be found here.