Megachile rotundata(F.) was used to study sublethal effects of carbaryl bran bait on a representative solitary nesting bee. Adult females were fed a 25% honey solution contaminated with 2 mg of commercially formulated carbaryl bran bait (2% [AI]) for 4 d and then were released into a greenhouse to nest in wooden blocks. Bees fed contaminated honey performed as well as bees fed plain honey solution. No differences were observed in number of days spent nesting, rate of cell production, offspring survival, investment in offspring, or offspring weight and sex ratio between carbaryl-treated and control bees. Diapausing bees from both carbaryl and control treatments tended to be larger than those emerging in the same season (emergent bees). We also found no sublethal effects onM. rotundatalarvae. Larvae fed provisions contaminated with 1 or 2 mg of carbaryl bran bait gained as much body weight as those fed uncontaminated provisions. We conclude that the 2% [AI] carbryl formulation of bran bait is likely to be the least detrimental to solitary bee pollinators of any insecticide thus far used to control grasshoppers on rangeland.