Lotmaria passim currently appears to be the predominant trypanosome in honey bees worldwide. Although, the specific effects of L. passim by single or mixed with other gut parasites such as Nosema ceranae on honey bees' health is still unclear. We consequently measured bees' survival, parasite loads, the expression of antimicrobial peptides (AMPs) and vitellogenin gene. Thus, (1) bees naturally infected with L. passim, (2) healthy bees inoculated with Nosema ceranae, (3) bees naturally infected with L. passim and inoculated with N. ceranae and (4) healthy bees (control) were maintained under controlled conditions. Honey bees infected with N. ceranae or with mixed infections of L. passim and N. ceranae had significantly lower survival rates than the control group at 20 days post-inoculation (dpi). A competitive suppression was also detected, provided that the L. passim load was significantly affected by the presence of N. ceranae at 15 dpi. Expressions of the AMPs defensin and hymenoptaecin rapidly (two hours post-inoculation) increased in bees infected with N. ceranae and mixed infections. However, this effect was not continuous. In fact, expressions of abaecin, defensin, hymenoptaecin and vitellogenin decreased drastically at 15 dpi in bees with both single and mixed infections. The decrease in the expression of AMPs and vitellogenin throughout this period was consistent with the reduced survivals observed in this study, indicating that mixed infections of L. passim and N. ceranae, and even into a scenario of competition between them, may have a synergic effect on the survival and immune-related gene expressions (biomarkers) of worker bees.
Keywords: AMPs; honey bee; lifespan; microsporidium; trypanosome; vitellogenin.