Species: Pteronarcys californica

This species has a semivoltine (2-, 3-, or rarely 4-year) life cycle including a 9-11 month diapause (Branham and Hathaway, 1975; DeWalt and Stewart, 1995; Freilich, 1991; Gaufin et al., 1972; Stewart and Stark, 2002). After three years in the water, mature nymphs emerge along the shoreline but emergence is earlier with higher water temperature (Gregory et al., 2000). Cold air temperature can kill emerging nymphs as was demonstrated on the Jocko River, Montana; where nymphs emerge earlier (early April through early May) than other streams in the United States (Rockwell and Newell, 2009). Emergence is timed with spring water temperature (Gregory et al., 2000). Small scale migration is heaviest near dawn and dusk. Adults are present in Alaska and western Canada mostly in May and June (Stewart and Oswood, 2006). Emergence time in the contiguous states is generally April to June (Stark et al., 1998), mid- to late May to as late as mid-June in eastern Idaho depending on water temperature (Gregory et al., 2000), early April through early May in northwestern Montana (Rockwell and Newell, 2009), and throughout May in southern Alberta (Townsend and Pritchard, 1998). It is on the wing in western mountains during June, July, and August (Needham and Claassen, 1925). Townsend and Pritchard (2000) studied aspects of egg development.