Little is known about the associations of ants (Hymenoptera: Formicidae) with subterranean aphids and mealybugs (Hemiptera: Sternorrhyncha: Aphididae and Pseudococcidae), particularly in Canadian grasslands. Knowledge of host plants for these sternorrhynchans is equally rare. We carried out a plant-based survey of ants and belowground aphids and mealybugs in a native fescue grassland in east-central Alberta, Canada. We found 23 species of ants, 12 of which (species of Lasius F., Myrmica Latreille, Tapinoma Förster, and Temnothorax Mayr) were in association with subterranean sternorrhynchans. Twelve species of aphids and mealybugs were collected; 3 are new records for Canada and 2 are possibly undescribed. Most ant species associated with sternorrhynchans were found with more than one species of sternorrhynchan, sometimes in the same nest. Almost all sternorrhynchans were found on graminoid hosts (Poaceae and Cyperaceae); there was little observed plant-specificity beyond this. There were no significant correlations between presence of subterranean sternorrhynchans and percent cover of different plant types, soil moisture content, slope, aspect, or visible entrances to ant nests.