PARENT SESSION
Poster Session #36: Seed Production, Recruitment, and Pollination.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Small scale foraging strata of wetland bees.

LEONG, JOAN^*,1, ¹ California State Polytechnic University, Pomona, CA

ABSTRACT- Previous studies have documented the existence of distinct foraging strata in bees foraging in vertically-structured vegetation. This study provides evidence for different foraging strata in wetland-inhabiting bees in the absence of much vertical vegetation structure. Bees were sampled by placing colored pan traps (blue, yellow and white) amidst nine populations of a low-growing, yellow-flowered, vernal pool plant species, Blennosperma nanum. Half of the traps were placed directly on the ground, at the same level as the flowers, while the other half were placed on tripods 0.5 meters above ground level. A total of 172 individuals were caught representing twenty-one bee species, the majority in the families Andrenidae, Anthophoridae, and Halictidae. Over 90% of all andrenids, and all anthophorids (mostly Synhalonia) were trapped at ground level. The "high" traps contained significantly more halictids, and trap color significantly influenced the number of halictids caught (ANOVA F=23.8, P<.001 and F=.3.5, P<.05 respectively). In addition, pollen grains of B. nanum were observed on 93% of andrenids, 53% of anthophorids, and 22% of halictids caught in traps. These results suggest that distinct foraging strata apparently exist for these pollinators at a surprisingly small vertical scale. Andrenids and anthophorids appear to forage at ground level only, while halictids forage within a wider vertical stratum. Trap height relative to the height of B. nanum flowers had a strong effect on the kinds and numbers of bees sampled.

KEY WORDS: bee, vernal pool, foraging height, pan trap