Overwintering Is Associated with Reduced Expression of Immune Genes and Higher Susceptibility to Virus Infection in Honey Bees



The eusocial honey bee, Apis mellifera, has evolved remarkable abilities to survive extreme
seasonal differences in temperature and availability of resources by dividing the worker
caste into two groups that differ in physiology and lifespan: summer and winter bees. Most
of the recent major losses of managed honey bee colonies occur during the winter, suggest-
ing that winter bees may have compromised immune function and higher susceptibility to
diseases. We tested this hypothesis by comparing the expression of eight immune genes
and naturally occurring infection levels of deformed wing virus (DWV), one of the most wide-
spread viruses in A. mellifera populations, between summer and winter bees. Possible inter-
actions between immune response and physiological activity were tested by measuring the
expression of vitellogenin and methyl farnesoate epoxidase, a gene coding for the last
enzyme involved in juvenile hormone biosynthesis. Our data show that high DWV loads in
winter bees correlate with reduced expression of genes involved in the cellular immune
response and physiological activity and high expression of humoral immune genes involved
in antibacterial defense compared with summer bees. This expression pattern could reflect
evolutionary adaptations to resist bacterial pathogens and economize energy during the
winter under a pathogen landscape with reduced risk of pathogenic viral infections. The out-
break of Varroa destructor infestation could have overcome these adaptations by promoting
the transmission of viruses. Our results suggest that reduced cellular immune function dur-
ing the winter may have increased honey bee’s susceptibility to DWV. These results contrib-
ute to our understanding of honey bee colony losses in temperate regions.

 

Steinmann N, Corona M, Neumann P, Dainat B (2015) Overwintering Is Associated with Reduced Expression of Immune Genes and Higher Susceptibility to Virus Infection in Honey Bees. PLoS ONE 10(6): e0129956. doi:10.1371/journal.
pone.0129956

Steinmann-et-al-2015-winter bees and viruses journal.pone.0129956.pdf
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0129956