Effects of Vairimorpha (Nosema) ceranae and Lotmaria passim on antimicrobial peptide expression in the digestive tract of honey bees (Apis mellifera L.)

Vairimorpha (Nosema) ceranae and Lotmaria passim are two commonly encountered digestive tract parasites of the Western honey bee (Apis mellifera L.). Although these parasites are associated with colony losses, little is known regarding how they affect the bee humoral defense response, particularly at the level of the digestive tract where the parasites are found. Using locally-obtained parasite isolates, the effects of both single and mixed V. ceranae and L. passim infections on the bee humoral defense response were evaluated at the digestive tract level by quantifying the expression of three antimicrobial peptides (apidaecin, defensin-1, hymenoptaecin) at five timepoints post-infection. Parasite density was also monitored in digestive tract tissues at these five timepoints to determine if the parasites, particularly L. passim, have distinct host tissue preferences. In general, it was found that bees do not elicit distinct humoral defense responses within the digestive tract in response to infection with either single or mixed V. ceranae and L. passim infections. Increased L. passim density in hindgut tissues compared to midgut tissues at each of the five timepoints suggests a hindgut preference for the parasite. Interestingly, for bees that received mixed infections, both L. passim and V. ceranae densities were elevated in hindgut tissues, suggesting that there could be an interaction occurring between the two parasites.