Regional, Annual, and Seasonal Variation in Pollinator Guilds: Intrinsic Traits of Bees (Hymenoptera: Apoidea) Underlie Their Patterns of Abundance at Vaccinium ashei (Ericaceae)

Abstract

We studied the numerical importance of bees as pollinators of rabbiteye blueberry, Vaccinium ashei Reade, in the southeastern United States. Most of the 27 bee species were rare at V. ashei flowers. Three taxa of bees were often abundant at V. ashei: the honey bee, Apis mellifera L.; queens of four bumble bee species (Bombus spp.); and the southeastern blueberry bee, Habropoda laboriosa (F.). Most bee species that co-occur with cultivated V. ashei do not visit its flowers either because adults emerge late in the spring following bloom, or their tongues are too short to probe the flowers effectively. The more common bees varied in their regional, annual, and seasonal abundances at cultivated V. ashei, reflecting inherent differences in sociality, foraging predilections, voltinism, and adult phenologies. Our censuses showed that H. laboriosa is a Vaccinium specialist (2 yr, two states, four habitats). Compared with the other common bees, abundance of H. laboriosa at V. ashei was most variable regionally, least variable annually, and most predictable daily during a flowering season. For 6 yr, adult activity of Bombus queens and univoltine H. laboriosa generally spanned the season of V. ashei flowering. Spatial patchiness but local reliability of H. laboriosa may be an outcome of its oligolectic floral preferences. In contrast, polylectic honey and bumble bees were regionally ubiquitous. However, the temporal abundance of honey bees fluctuated markedly at V. ashei, perhaps reflecting their shifting preferences among competing members of a local flora.