During 1965–66, studies of a large population of Hylastes nigrinus (Mannerheim), breeding in roots and stumps of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, killed by Dendroctonus pseudotsugae Hopkins in 1964, were conducted on Marys Peak in western Oregon, near the city of Corvallis.
The emergence and flight of H. nigrinus were at their maximum in late April and early May. Emergence was strongly influenced by temperature and seldom occurred at temperatures below 61° and above 75°F. Flight behavior was strongly affected by light intensity, peaking at intensities between 300 and 1200 ft-c during the late afternoon or early evening. Maturation feeding was found to take place on small roots of dead, old Douglas-fir and on roots of young Douglas-fir weakened after replanting. Egg-galleries, normally running parallel with the grain of the wood, were initiated in June and eggs were kid from the end of that month. Five larval instars were found. Adult beetles as well as full-grown larvae overwintered in the galleries. The majority of the population completed development in 1 year.
The larval population of H. nigrinus was heavily decimated during the fall of 1965 by larvae of the dipteron fly, Medetera vidua Wheeler (Doliohopodidae). Emergence data are presented for scolytid, curculionid, cerambycid, and buprestid species competing with H. nigrinus in stumps or roots.