Tolerance of honey bee adults and larvae toward tyrothricin peptides derived from Brevibacillus parabrevis

Tyrothricin is a peptide complex containing the linear gramicidins and cyclic tyrocidines. The tyrocidines have potent activity against fungal plant pathogens. As these peptides have possible agricultural applications, their toxicity was evaluated toward honey bee adults and larvae. Tyrothricin formulated in sucrose was non-toxic to caged adult honey bees at up to 1.5 g/L over 48-h exposure, which is 100- to 200-fold higher than the amount needed to eradicate high fungal loads (2 × 10 4 spores/mL). Moreover, tyrothricin and the tyrocidines displayed potent in vitro activity toward foulbrood causing pathogens ( Paenibacillus larvae , Melissococcus plutonius , Paenibacillus alvei ) in honey bee larvae. In vivo tyrothricin or tyrocidine treatment delayed infection onset, indicating potential for curing. Tyrothricin was also found to be non-toxic with possible protective action in a semi-field trial on young bees released into hives, indicating the relative safety of the application of these antimicrobial peptides in an agricultural setting.