Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) is an important natural enemy of root maggots (Delia spp.) (Diptera: Anthomyiidae), which are serious pests of brassicaceous crops in North America and Europe. Adults of A. bilineata feed on eggs and larvae of root maggots, and A. bilineata larvae parasitize Delia spp. pupae. Emergence and seasonal activity patterns of A. bilineata were investigated during 2003–2005 in canola (Brassica rapa L. and Brassica napus L.) in central Alberta, Canada, in relation to degree-day (DD) accumulations and Julian date. Captures of A. bilineata adults from pitfall traps within emergence cages situated over canola stubble from the previous year indicated that ≈428, 493, and 455 DD (soil base 5.57°C) and 187, 189, and 180 Julian days were required for 50% emergence in 2003, 2004, and 2005, respectively (3-yr mean = 185.1 ± 2.8 Julian days [SEM]). Captures of A. bilineata adults from pitfall traps placed in current canola crops determined that 50% levels of activity density required 379 DD and 180 Julian days in 2004. A logistic model that described the relationship of degree-days and Julian days with emergence of adult beetles was appraised, and good correspondence was evident between predicted and observed cumulative emergence patterns. Emergence and seasonal activity periods of A. bilineata in canola were well synchronized with occurrence of preimaginal life stages of its principal hosts, Delia radicum (L.) and Delia platura Meigen, with beetle emergence beginning shortly after the onset of root maggot oviposition.