Sampling native bees in proximity to a highly competitive food resource (Hymenoptera: Apiformes)

The efficacy of sweeping and vacuuming as methods of sampling native bees were compared to those of passive blue and yellow translucent-vane traps located adjacent to a highly attractive forage source, Helianthus spp. (Asteraceae). A total of 35 species of native bees belonging to 12 genera were caught during September, 94 in the passive blue-vane traps, 63 by sweeping, and 54 by vacuuming and yellow-vane traps. Overall, 55.7 of all the native bees trapped in the study across the four treatments were collected in the blue vane traps. There were almost double the number of species, and over five times more individuals in blue vane traps than in the yellow. Agapostemon virescens (Fabr.) was the predominant species collected across all methods (400 of 1208). The majority of females (> 99) captured in the blue vane traps lacked pollen suggesting that the bees may have been diverted by the reflected light from the trap during their flight to the floral sources rather than on their return flight to the nest. Very few Apis mellifera (L.) were taken in the traps, whereas they dominated in sweeping and vacuuming samples. These studies suggest that the blue vane traps can serve as an effective sampling tool for bee diversity studies in proximity to stands of intense floral competition.