Sublethal effects of commercial plant protection product containing spores Bacillus amyloliquefaciens QST 713 (formerly subtilis) on winter adult honeybees

The aim of this study was to assess potential harmful lethal and sublethal effects of commercial plant protection product containing Bacillus amyloliquefaciens QST 713 (formerly subtilis ) spores on winter adult honeybees according to OECD 245 (2017). Caged winter honeybees fed 10 days with a sucrose solution (50% w/w) ad libitum spiked with a maximum application field rate of 1/1 and its 1/10 showed no dose-dependent mortality under laboratory conditions; the No Observed Effect Concentration (NOEC) appears to be higher than or equal 4 × 10 7 colony-forming unit (CFU)/ml diet, resp. 4 × 10 10 CFU/l diet. Although the results of Denaturing Gradient Gel Electrophoresis (DGGE) analysis showed no significant changes in the composition of gut bacterial community between untreated control and experimental groups after 10 days of chronic exposure, the expression of genes encoding antimicrobial peptides was decreased in one/both treated groups in comparison with untreated control group; significantly lower results of expression were detected in genes for Apidaecin, Defensin-1, and Hymenoptaecin. Despite no direct lethal effect of commercial plant protection product containing Bacillus amyloliquefaciens , QST 713 was observed in adult bees following chronic exposure; the decrease in some immunity parameters observed in tested winter bees may potentially impair bee colony health and survival.