Molecular characterization and pathogenicity of fungal isolates against the small hive beetle (Aethina tumida) a destructive pest of honey bee (Apis mellifera) colonies

The small hive beetle (SHB) Aethina tumida, an invasive species from sub-Saharan Africa, was confirmed in the Southeastern United States in Florida in 1998 and has become a serious pest of honey bees. This destructive insect has already invaded more than 30 states, and threaten the honey bee industry in the southern US. The chemicals currently used for the control of SHB are not effective and leave residues in honey products. This study was designed to identify unknown fungal pathogens from dead SHB and develop a sustainable and environmentally friendly alternative control strategy for SHB. Dead SHB were collected from several commercial apiaries in Florida; they were surface-sterilized and plated in Petri dishes containing Sabouraud Maltose Agar and yeast (SMAY), and incubated for 3-10 days to investigate the recovery of primary causal agents. The unknown fungi from dead SHB were identified using DNA fingerprinting techniques and were tested against SHB in spray tower and soil-based bioassays. The analysis of DNA sequences from unknown fungi revealed two potential biological control agents, Metarhizium anisopliae and Beauveria bassiana. In spray tower bioassays, the LC₅₀ for M anisopliae was 0.8 x 10⁶ and 1.0  x 10⁴ conidia ml^-1 for larvae and adults respectively. The LC₅₀ for B. bassiana was 1.0 x 10⁷ and 2.0 x 10⁵ conidia ml^-1 for larvae and adults respectively. In soil bioassays, 100% mortality of SHB occurred within 21 days post treatment for both fungi. Thus, these fungal pathogens offer new and environmental sound avenues for successful control of SHB in honey bee colonies.