Use of Crape Myrtle, Lagerstroemia (Myrtales: Lythraceae), Cultivars as a Pollen Source by Native and Non-Native Bees (Hymenoptera: Apidae) in Quincy, Florida

Abstract

Crape myrtle, Lagerstroemia species (Myrtales: Lythraceae), has become a dominant flowering plant in the ecosystems of the southeastern USA. Examination of flower records for bees shows few records of pollinators visiting these species even though they produce dimorphic pollen. Sampling of bees from a multi-cultivar crape myrtle planting at the University of Florida's Institute of Food and Agricultural Sciences, North Florida Research & Education Center in Quincy, Florida, via established transect walks in 2009 and 2010, and intensive net collecting in 2011, indicated that bee species from several functional groups (based on taxonomy, body size, and sociality) visited crape myrtle. Results also indicated that crape myrtle cultivars were used differently by the following major bee species (Hymenoptera: Apidae): the honey bee, Apis mellifera L.; the bumble bees Bombus impatiens Cresson and Bombus fraternus (Smith); and the carpenter bees Xylocopa micans Lepeletier and Xylocopa virginica (L.). Numbers of the native bumble bee species varied significantly between years whereas those of honey bees did not. All bee species displayed a marked preference for specific cultivars through time. Bombus impatiens exhibited a very patchy distribution related to the availability of bahiagrass flowering in the understory; these bees used bahiagrass but quickly returned to crape myrtle when bahiagrass was mowed. This suggests that the relationship between this pollinator and the non-native crape myrtle is a weak interaction and a number of unstudied factors may be affecting it. The presence of artificial colonies of B. impatiens resulted in a patchy distribution of these bees nearest the colonies. In contrast, the presence of a honey bee colony near the plot had no effect on honey bee numbers or distribution within the plot. Crape myrtle appears to provide a pollen source for several native bee species as well as for honey bees. Evidence suggests that certain combinations of crape myrtle cultivars could provide additional spatial and temporal support for a diversity of functional groups of pollinators and may augment pollinator species richness. Moreover, as crape myrtle blooms during summer months when other pollen sources are scarce, it has great potential to alleviate stress on pollinators due to food shortages. This work is congruent with previous research demonstrating that crape myrtle supports a large number of beneficial insects, and it further defines the importance of this non-native plant species in impacting several regulating ecosystem services.