Pathogenicity bioassays of Ascosphaera apis strains from Spanish provinces in bee larvae from Northern Argentina

Abstract

Beekeeping is one of the main economic activities in several countries, and Argentina has become one of the most important exporters of honey and other products from hives. Ascosferosis, an emerging disease caused by the fungus Ascosphaera apis, affects bee larvae, causing mortality in the colonies. While many studies have focused on the infections of European Apis mellifera bees, we studied hybrid Apis mellifera scutellata bees from northern Argentina and fungal strains isolated from commercial pollen from Spanish provinces, to determine the susceptibility of local bees to the entomopathogenic A. apis. Different groups of larvae were administered sugar syrup suspensions with ascospores at different concentrations: a lower concentration of 5 × 103 spores/mL was used to know the susceptibility of the larvae and a higher concentration of 5 × 106 spores/mL was used to determine the pathogenicity, resulting in an average infection of 30% of the mummified larvae. Besides, an intermediate concentration of 5 × 104 spores/mL was administered, which allowed us to identify the most pathogenic strain at this concentration. This work provides the first approximation to the pathogenic effect of Spanish fungal strains on larvae of bees from northern Argentina.