Identification of Immune Regulatory Genes in Apis mellifera through Caffeine Treatment

SIMPLE SUMMARY: The preference of honeybees to consume nectar with caffeine has been recorded. To investigate the effects of caffeine to this important pollinator, we first focus on the influences on immunity which is seldom explored in insects regarding caffeine. In our results, we discovered the suppressive effects on viral pathogens and the boosting effects on immunity after caffeine treatment. At least six different latent-infecting viruses in Taiwan were suppressed by caffeine. Nevertheless, the enhancement on immunity may not be effective if the bees have not been exposed to the environment or potential natural secondary metabolites like caffeine. These findings provide a basic but valuable insight into how caffeine can aid honeybees in fighting against viral invasion. ABSTRACT: Plants and pollinators are mutually beneficial: plants provide nectar as a food source and in return their pollen is disseminated by pollinators such as honeybees. Some plants secrete chemicals to deter herbivores as a protective measure, among which is caffeine, a naturally occurring, bitter tasting, and pharmacologically active secondary compound. It can be found in low concentrations in the nectars of some plants and as such, when pollinators consume nectar, they also take in small amounts of caffeine. Whilst caffeine has been indicated as an antioxidant in both mammals and insects, the effect on insect immunity is unclear. In the present study, honeybees were treated with caffeine and the expression profiles of genes involved in immune responses were measured to evaluate the influence of caffeine on immunity. In addition, honeybees were infected with deformed wing virus (DWV) to study how caffeine affects their response against pathogens. Our results showed that caffeine can increase the expression of genes involved in immunity and reduce virus copy numbers, indicating that it has the potential to help honeybees fight against viral infection. The present study provides a valuable insight into the mechanism by which honeybees react to biotic stress and how caffeine can serve as a positive contributor, thus having a potential application in beekeeping.