Nesting biology of two sympatric species of Megachile (Chrysosarus) (Megachilidae) in Argentina

Abstract

Leaf cutter bees (genus Megachile) are a diverse group of pollinators of wild and cultivated plants. Many species nest in pre-existing cavities and use diverse building materials to construct their brood cells. For instance, species of subgenus Chrysosarus add a mud layer between two layers of leaves or petals. We studied similarities and differences in their nesting biology from 13 nests of Megachile (Chrysosarus) concava and 72 nests of Megachile (C.) diversa (Megachilidae) obtained in trap nests in northern Argentina. Females of M. concava used trap nests with higher diameters, shorter length, and built a lower number of brood cells per nest compared to females of M. diversa. In the latter species, the sex ratio was female-biased, but we observed male-biased progeny in shorter trap nests, thus the sex ratio of M. diversa could be context-dependent. Reproductive success was different between species: 40.5% for M. concava and 75.8% for M. diversa, desiccation and/or mold being the principal factor of mortality of immature stages. The attack from parasitic species represented 10.8% for M. concava and only 1.2% for M. diversa. Megachile concava, based on observations of a few nests collected during autumn, could be a bivoltine species and oligolectic of Faboideae, while M. diversa is a partially bivoltine or multivoltine, and polylectic species, with a marked turnover of pollen resource throughout its extensive reproductive season. Differences in the trophic niche and, to a lesser extent, in the inner diameter of trap nests used could allow their coexistence in the studied forests.

Keywords:

• leaf cutter bees
• solitary bees
• trap nest
• sympatry

Acknowledgments

To the family Götz and Alparamis S.A. for the permission to conduct this study in Reserva El Bagual, and to A. Di Giacomo for logistical support. To L.I. Pérez for his help in the field, S. Durante and A. Roig Alsina for their collaboration in the determination of Megachile and Coelioxys species, respectively; R. González-Vaquero, V.H. González and two anonymous reviewers provided constructive criticism to previous drafts and A. Torretta and R.I. Saurral for help with the English revision. JPT & HJM are affiliated to CONICET, Argentina.

Disclosure statement

The authors declare that they have no conflict interest.

Additional information

Funding

We thank the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and the Universidad de Buenos Aires for financial support through grants PIP 11220110100312 and UBACyT 20020130200203BA, respectively.