Foraging behavior and floral preference of Melissodes tepaneca
One of the chief drivers of wild pollinator decline is diminishing natural habitat and floral resource availability through increased human land use. Native, solitary bees provide a significant portion of pollination services for animal pollinated crops, yet comparatively little is understood of their foraging behavior or dietary breadth in comparison to their managed, non-native counterparts. Understanding the patterns of resource use among native bees in areas undergoing increased urbanization and agricultural intensification will provide valuable insight into wild pollinator conservation and management practices. Our study examines the floral resource usage of Melissodes tepaneca, a solitary species with a generalist diet that ranges across the eastern and southern US. We investigate floral resource usage across local (50m) and landscape scales (1km) by sampling, imaging, and identifying pollen loads on 68 individuals from 10 sites across south and central Texas. In each site, two observers net-collected bees within a 50 m2plot for 15 minutes, and pan-trapped for 24 hours during three periods, in May, June, and July of 2012. We also conducted exhaustive vegetation surveys in each plot, documenting floral density and diversity, and collecting anthers for the pollen reference collection. Insects were pinned and identified, then pollen loads were extracted via vortexing insects in ethanol, preening scopa, and centrifugation of the pollen-ethanol solution. Pollen loads were imaged using fuchsine dye, identified to species using the pollen reference, and then counted to a maximum of 300 grains per sample.
Our results indicate that the diet of M. tepanaca was comprised largely of Gaillardia pulchella, Cirsium texanum, and Monarda citriodora (mean 2.1%, 1.14%, 0.4%, respectively). This collection of pollen was not proportional to the composition of the available floral resources at local or landscape-scales. Floral abundance at both local and landscape scales was not a significant indicator of composition within the M. tepaneca pollen loads. M. tepaneca foraged primarily on G. pulchella, C. texanum, and M. citriodora, even in sites where the species were not abundant at local or landscape scales (mean 0.39%, 0.02%, 0.13%, respectively). We found that similar species dominated the diets of M. tepaneca, regardless of whether specimens were caught by net or in pan-traps. These results are indicative of a resource preference in M. tepanaca, and suggest that both netting and pan-trapped specimens provide comparable information regarding the pollen usage of native bees.