Eastern carpenter bees (Xylocopa virginica) are experiencing wing discoloration, with St. Louis, MO as a hotspot

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Madeleine F. Thompson, Nina S. Fogel and Gerardo R. Camilo, Department of Biology, Saint Louis University, St. Louis, MO

Background/Question/Methods
Cities are novel environments that provide never encountered challenges to plants and animals. How organisms respond to these challenges is a newer avenue of research in ecology and evolution. The Eastern carpenter bee, Xylocopa virginica, is the largest, and one of the most common, bee species in eastern North America. The species thrives in cities due to abundant sources of accessible wood that they use for nesting. Within the urbanized area of St. Louis, MO, USA, over 10% of individuals have a unique wing discoloration that causes portions of the wings to be translucent.
Our objective is to provide foundational information on the morph by (1) quantitatively describing the manifestation of the wing morph and (2) investigating the prevalence of the morph in the species’ home range. We photographed the right forewing of 88 specimens captured in St. Louis with the wing discoloration to quantify the pattern of discoloration. The variation among the morphs was then calculated using the R package ‘patternize’ and compared to standard dark wing individuals. We also searched the 25,000+ observations of X. virginica on iNaturalist to document the prevalence and potential spread of the morph within the species’ range.

Results/Conclusions
Color pattern analysis shows the morph’s presence is not an all-or-none phenomenon, but follows a generalized gradient. When present, the discoloration is most commonly found at the distal and posterior region of the forewing. Vascularized portions located anteriorly and proximally on the wing rarely exhibited discoloration. Occurrence results from iNaturalist show the presence of the morph is concentrated around urban centers in at least 28 states and one Canadian province within the species’ range. However, St. Louis had one of the highest proportions of individuals with the morph. Since wings in bees serve thermoregulation purposes, we posit that this morph detected in X. virginica may possess a fitness advantage in urban settings, unlike other manifestations of clear wings that result from disease and deleterious mutations.
As locations around the globe become increasingly urbanized, human expansion’s impact on wildlife fitness is of increasing concern and importance. Our findings on the manifestation and prevalence of the morph will guide continued research in examining the underlying mechanism and the role of urbanization in this phenomenon. Future research can identify the potential impacts urbanization may be having on urban pollinators, including how they and other species could be adapting to anthropogenic changes