Taxonomy and color variation in Brazilian Agapostemon bees (Apidae, Caenohalictini)

Abstract

The identification of females in the sister species Agapostemon chapadensis Cockerell, 1900 and Agapostemon semimelleus Cockerell, 1900 has historically been challenging, with metasomal coloration serving as the primary distinguishing feature. However, extensive intraspecific variation observed in this trait has highlighted its unreliability as a diagnostic character. This study analyzed 727 specimens of both species, integrating morphological traits and geographic distribution to delimit species boundaries and investigate color variation. New diagnostic characters, subtle pubescence patterns – such as setae length and distribution in both sexes – are proposed to reliably differentiate the species. Agapostemon chapadensis is largely restricted to Cerrado regions, with individuals typically exhibiting amber-colored metasoma, while A. semimelleus is more widespread, predominantly displaying black metasoma. The observed variation in metasomal coloration may reflect environmental adaptations, as responses to climate or predation pressures. Further research is recommended to elucidate the ecological and evolutionary drivers of these color variations.The identification of females in the sister species Agapostemon chapadensis Cockerell, 1900 and Agapostemon semimelleus Cockerell, 1900 has historically been challenging, with metasomal coloration serving as the primary distinguishing feature. However, extensive intraspecific variation observed in this trait has highlighted its unreliability as a diagnostic character. This study analyzed 727 specimens of both species, integrating morphological traits and geographic distribution to delimit species boundaries and investigate color variation. New diagnostic characters, subtle pubescence patterns – such as setae length and distribution in both sexes – are proposed to reliably differentiate the species. Agapostemon chapadensis is largely restricted to Cerrado regions, with individuals typically exhibiting amber-colored metasoma, while A. semimelleus is more widespread, predominantly displaying black metasoma. The observed variation in metasomal coloration may reflect environmental adaptations, as responses to climate or predation pressures. Further research is recommended to elucidate the ecological and evolutionary drivers of these color variations.