Stelis montana
Pest description A cleptoparasitic bee (adults 8 to 10 mm) of which the larvae steal food provisions from the host. Female adults lay eggs in uncapped BOB cells while the BOB females are away foraging. Cuckoo bee larvae kill BOB larvae and consume the pollen-nectar provision. Only one parasite develops in each cell.
Management Cuckoo bee pupae may be identified by inspecting semi-translucent straws against a light bulb. Cuckoo bee frass is long and curly and cocoons are harder than those of BOB. Infected straws containing cuckoo bee pupae may be dissected and removed effectively. Larger nest blocks (96-cavity) have been shown to produce more BOB progeny with lower parasitism rates compared to smaller nest blocks (15-cavity).