First reported incidence of Bacillus velezensis exhibiting effective antagonism against a blowfly species, Lucilia cuprina

Bacillus sp. PHP1601 (Bacillales: Bacillaceae), a member of the B. subtilis sensu lato, possesses an interesting ability to antagonise fly larvae. Blowflies are considered occupational nuisances and recognised as vectors of disease. A study was undertaken to evaluate the biocontrol potential of Bacillus sp. PHP1601 against Lucilia cuprina (Wiedemann) (Diptera, Calliphoridae) larvae. Bioassays were established to determine the biocontrol efficacy of various treatment formulations, i.e., vegetative cell (10²–10¹⁰ cells g⁻¹), endospore (10²–10¹⁰ endospores g⁻¹), cell-free supernatant (1–30% v w⁻¹) and crude biosurfactant extract (5–1000 μg g⁻¹) against second instar L. cuprina fly larvae reared on milk agar medium. All treatments demonstrated a dose-dependent larvicidal response over a 240 h period. Even at the lowest cell and endospore concentrations tested (i.e., 10² cells/endospores g⁻¹) the pupation stage was inhibited, effectively interrupting the fly reproduction cycle. Larvae antagonism elicited by partially purified biosurfactant extracts indicated the likely contribution of bioactive lipopeptide compounds to the mechanism of inhibition. Larvae cadavers recovered from these treatments displayed substantial physiological discolouration and lacked structural integrity. PHP1601 was confirmed to be a strain of B. velezensis based on multiple-locus sequence analysis of 16S rRNA, gyrA, rpoB and dnaJ housekeeping genes. This study constitutes the first report of a strain of B. velezensis demonstrating a larvicidal response towards a member of the suborder Brachycera.