In the temperate climates of middle Europe and North America, two distinct honeybee (Apis mellifera) populations are found in colonies: short-living summer bees emerge in spring and survive until summer, whereas long-living winter bees emerge in late August and overwinter. Besides the difference in their life spans, each of these populations fulfills a different role in the colonies and individual bees have distinct physiological and immunological adaptations depending on their roles. For instance, winter worker bees have higher vitellogenin levels and larger reserves of nutrients in the fat body than summer bees. The differences between the immune systems of both populations are well described at the constitutive level; however, our knowledge of its inducibility is still very limited. In this study, we focus on the response of 10-day-old honeybee workers to immune challenges triggered in vivo by injecting heat-killed bacteria, with particular focus on honeybees that emerge and live under hive conditions. Responses to bacterial injections differed between summer and winter bees. The latter induced more intense response, including higher expression of antimicrobial genes and antimicrobial activity, as well as a significant decrease in vitellogenin gene expression and its concentration in the hemolymph. The intense immune response observed in winter honeybees may contribute to our understanding of the relationships between colony fitness and infection with pathogens, as well as its association with successful overwintering.

European foulbrood (EFB) is an infectious disease of honey bees caused by the bacterium Melissococcus plutonius. A method for DNA isolation and conventional PCR diagnosis was developed using hive debris, which was non-invasively collected on paper sheets placed on the bottom boards of hives. Field trials utilized 23 honey bee colonies with clinically positive symptoms and 21 colonies without symptoms. Bayes statistics were applied to calculate the comparable parameters for EFB diagnostics when using honey, hive debris, or samples of adult bees. The reliability of the conventional PCR was 100% at 6.7 × 10³ Colony Forming Unit of M. plutonius in 1 g of debris. The sensitivity of the method for the sampled honey, hive debris, and adult bees was 0.867, 0.714, and 1.000, respectively. The specificity for the tested matrices was 0.842, 0.800, and 0.833. The predictive values for the positive tests from selected populations with 52% prevalence were 0.813, 0.833, and 0.842, and the real accuracies were 0.853, 0.750, and 0.912, for the honey, hive debris, and adult bees, respectively. It was concluded that hive debris can effectively be utilized to non-invasively monitor EFB in honey bee colonies.

The green microalga Chlorella vulgaris Beijerinck (Chlorellaceae) is widely used as a food supplement for humans and animals. In beekeeping practice, Chlorella vulgaris has potential as a pollen supplement. We studied whether Chlorella extracts display antimicrobial properties against Paenibacillus larvae, the causative agent of the honey bee bacterial disease American foulbrood. We identified components responsible for antimicrobial activity and evaluated the added values of Chlorella as a food supplement for honey bees. Different extracts (water, acetone, methanol) were prepared from Chlorella biomass (phototrophically and heterotrophically cultivated) and screened for antimicrobial activity against ERIC I and ERIC II genotypes of P. larvae. Active acetone extracts of phototrophically cultivated Chlorella vulgaris biomass were fractioned via preparative reverse-phase chromatography. Antimicrobial activity was detected for 9 of the resulting 33 fractions. Further analysis revealed the chemical composition of the active fractions. C. vulgaris extracts showed a significant antimicrobial effect against vegetative cells and spores of P. larvae strains of ERIC I and ERIC II genotypes. The lowest MIC of the most active acetone extract was 6.3 µg/mL for both tested genotypes. In the majority of the active fractions, monolinolenin, fatty acid linoleic acid, and methyl esters of linoleic and/or palmitic acid were identified via high-performance liquid chromatography coupled with high-resolution mass spectrometry analysis. Based on our results, we concluded that algal C. vulgaris food supplements not only contain nutritional but also potential prophylactic properties for honey bee health.

Humic substances (HS) are increasingly investigated as natural additives to support health in humans and animals, yet their effects on honey bees remain insufficiently characterised. This study evaluated the impact of a commercial HS-based product on immunity and oxidative status of Apis mellifera . Newly emerged worker bees were kept under laboratory conditions and fed sugar syrup supplemented with 0.5% HS for seven days, while the control group received unsupplemented syrup. Effects of HS were evaluated by analysing the expression of selected immune-related genes, quantifying antimicrobial peptides (AMPs), measuring the activity of antioxidant enzymes, evaluating lipid peroxidation, and characterising hemocyte populations. HS supplementation significantly increased relative gene expression of superoxide dismutase 1 and prophenoloxidase , while expression of genes for apidaecin and defensin 1 decreased. HS supplementation significantly increased relative gene expression of superoxide dismutase 1 and prophenoloxidase , while expression of genes for apidaecin and defensin 1 decreased. Similarly, catalase enzymatic activity was significantly decreased in the HS group. No significant changes were detected in gene expression for other AMPs and relative abundance of AMPs, or other antioxidant parameters. HS supplementation significantly increased the proportion of medium granular hemocytes ( p < 0.05) at the expense of high granular cells ( p < 0.01). In conclusion, the 7-day administration of HS at 0.5% did not adversely affect bee health and modulated selected immune parameters. The biological significance of these immunomodulatory effects requires confirmation through challenge studies and field trials under natural conditions.