Stonebrood in Argentinian wild bees: A neglected disease?

Wild bees serve as essential pollinators for a vast array of flowering plants, with approximately 1,200 distinct species inhabiting the diverse ecosystems of Argentina. Prior research has shown that the intricate complex of pests and pathogens attacking honey bees is widely recognized and documented by the scientific community. However, the specific interactions between fungal pathogens and wild bee fauna remain largely unexplored in current entomological literature. Fungal agents such as those belonging to the Aspergillus genus represent a potential threat that has received minimal attention compared to bacterial or viral infections. The ecological stability of solitary ground-nesting bees depends on understanding these biological pressures within their natural nesting environments. Existing studies frequently overlook the mycological aspects of larval development in non-managed bee species. This absence of evidence motivated a focused examination of the nesting biology and health challenges faced by wild bee populations in the Buenos Aires region.

This investigation evaluates the nesting biology of two solitary ground-nesting wild bee species to determine the factors influencing their survival. The researchers sought to quantify the impact of Aspergillus flavus infections on the mortality rates of larvae within these subterranean environments. By examining brood cells from multiple localities, the study identifies the primary biological agents responsible for larval death. The work specifically targets the knowledge gap regarding how fungal pathogens like Aspergillus influence the survival of Melitoma segmentaria and Ancyloscelis halictoides. Scientists documented the presence and influence of various parasitoids and cleptoparasites that inhabit the same nesting aggregations. This effort provides a detailed record of the developmental hurdles encountered by these pollinators during their vulnerable larval and pupal stages. The study establishes a necessary framework for discussing the broader implications of stonebrood disease within South American wild bee communities.

The experimental process began with the excavation of brood cells from two separate nest aggregations located in different areas of Buenos Aires. These isolated cells were placed in plates and subjected to daily monitoring to track the progression from larvae to adult emergence. Scientists recorded comprehensive data regarding the species identity, collection date, sex, and the presence of any associated parasitoids or cleptoparasites. To identify the causes of death, pollen masses along with dead larvae and pupae were photographed and preserved for microbiological testing. The researchers cultured these biological samples on Yeast-Glucose-Starch-Agar (YGPSA) media plates to isolate and identify fungal growth. Molecular identification involved extracting Deoxyribonucleic Acid (DNA) with a specific commercial kit followed by Polymerase Chain Reaction (PCR) amplification using targeted primers for sequencing. This methodological approach allowed for the precise identification of the fungal species responsible for the observed stonebrood symptoms.

Aspergillus flavus emerged as the most frequent cause of mortality for the wild bee larvae across both studied localities. The investigation revealed three distinct biological threats to the developing bees: the fungus A. flavus, the parasitoid Leiopodus lacertinus, and the parasite Melittobia hawaiiensis. This discovery represents the inaugural record of A. flavus inducing stonebrood disease in wild bee populations throughout South America. The data provided new insights into the nesting biology and reproductive challenges of Melitoma segmentaria and Ancyloscelis halictoides. Microbiological and molecular analyses confirmed the presence of the fungal pathogen in the affected brood cells and pollen masses. Mortality estimates indicated that fungal infections posed a greater risk to larval survival than the recorded insect parasitoids and cleptoparasites. These results demonstrate that stonebrood is a significant, yet previously neglected, factor in the population dynamics of Argentinian ground-nesting bees.

The findings emphasize that Aspergillus flavus is a significant pathogen that impacts the health and survival of solitary wild bees. This research highlights the necessity of including fungal diseases like stonebrood in future assessments of pollinator population declines. The identification of this pathogen in Melitoma segmentaria and Ancyloscelis halictoides suggests that other wild bee species may also be at risk. These results open up essential discussions regarding the environmental factors that facilitate the spread of Aspergillus within ground-nesting bee aggregations. The study underscores the importance of monitoring both fungal and insect-based mortality factors to ensure the conservation of Argentinian bee diversity. Future investigations should explore the transmission pathways of stonebrood between different bee species and their nesting substrates. The authors conclude that addressing these neglected diseases is vital for maintaining the pollination services provided by the 1,200 wild bee species in the region.