The effect of temperature on the duration of egg, larval, prepupal, and pupal development of the predator Laricobius nigrinus Fender was studied at six constant temperatures (6, 9, 12, 15, 18, and 21°C) where Adelges tsugae Annand was used as prey. Developmental time was inversely proportional to temperature between 6 and 18°C. Laricobius nigrinus did not complete development at 21°C. Significant positive linear relationships were observed between developmental rate and temperature for all life stages. Minimum developmental threshold temperatures were estimated at 5.4°C for eggs, 3.2°C for larvae, 2.9°C for prepupae, and 3.1°C for pupae. Median development times for eggs, larvae, prepupae, and pupae were 59.5, 208.3, 217.4, and 212.8 degree-days (DD) above minimum developmental temperatures, respectively. Development from oviposition to adult eclosion required a minimum temperature of 3.7°C and 666.7 DD. A degree-day model, developed in the laboratory for predicting egg hatch, predicted a degree-day value that was within 4 d of the median egg hatch observed at two field sites in 2000. This regression model is a useful predictor of egg hatch in Victoria, British Columbia, Canada. In addition, the lower development threshold from egg to adult for L. nigrinus (3.7°C) is similar to that for the A. tsugae progrediens (spring) generation from second instar to adult (3.9°C), indicating that L. nigrinus and A. tsugae are adapted to similar climatic regimes.