Stonebrood in Argentinian wild bees: A neglected disease?

Wild bees are crucial for pollinating flowering plants, with about 1,200 species found in Argentina. While the complex of pests and pathogens that attack honey bees are widely known, few studies have investigated fungal pathogens such as Aspergillus in wild bee fauna. This study focuses on understanding the nesting biology of two solitary ground-nesting wild bees and sheds light on the impact of fungal infections caused by Aspergillus flavus on larval mortality in these bees. Brood cells were excavated from two aggregations of nests from two localities in Buenos Aires, Argentina. Cells were isolated in plates and monitored daily until adult emergence. Data on species, date, sex, and presence of parasitoids and cleptoparasites were recorded, and the total mortality due to insects and fungal pathogens was estimated. Pollen masses, larvae, and dead pupae were photographed and stored for microbiological analysis. Samples were cultured on yeast-glucose-starch-agar (YGPSA) in media plates. In positive samples, DNA was extracted using a specific commercial kit. Molecular analysis involved PCR amplification and sequencing, utilizing specific primers. Data on the nesting biology of Melitoma segmentaria and Ancyloscelis halictoides were presented. We identified three causes of mortality: Aspergillus flavus, Leiopodus lacertinus, and Melittobia hawaiiensis. The most prevalent cause of mortality in both study sites was A. flavus, the first record of this fungus causing stonebrood in wild bees of South America. Our findings open up discussions on the importance of this fungal pathogen for the health of wild bees.