Honey bees use different sets of genes, regulated by two distinct mechanisms, to fight off viruses, bacteria and gut parasites, according to researchers at Penn State and the Georgia Institute of Technology.
The findings may help scientists develop honey bee treatments that are tailored to specific types of infections. “Our results indicate that different sets of genes are used in immune responses to viruses versus other pathogens, and these anti-viral genes are regulated by two very distinct processes—expression and DNA methylation,” said David Galbraith, a graduate student in entomology, Penn State. The results will appear in today’s (Mar. 26) issue of PLOS Pathogens.
According to Christina Grozinger, director of the Penn State Center for Pollinator Research, beekeepers lose an average of 30 percent of their colonies every winter and an average of 25 percent in the summer.
“Honey bees have more than 20 types of viruses, and several of them have been linked to losses of honey bee colonies,” she said. “Yet, beekeepers currently do not have any commercially available methods to reduce viral infections.” With a goal of uncovering which genes increase or decrease their activity in response to the presence of viruses, the researchers measured expression levels of all genes in the honey bee genome in both infected and uninfected bees. They found that the RNAi pathway had increased activity and, therefore, is likely an important anti-viral immune pathway in bees.
“Previous studies suggested the RNAi pathway was involved in anti-viral immune responses in bees, but we showed that expression levels of many genes in this pathway are significantly higher in virus-infected bees,” said Grozinger. “The RNAi pathway helps to cut up and destroy viral RNA so it is not infectious.” Scientists and beekeepers are increasingly interested in using RNAi approaches to control viruses and parasites in agricultural crops and in honey bee colonies, according to Grozinger.
“We will need to make sure that any artificial RNAi approaches do not interfere with the natural anti-viral RNAi mechanisms in honey bees,” Grozinger said. In addition to examining gene expression in virus-infected versus uninfected honey bees, the researchers also scanned the honey bee DNA for extra methylation marks that may have been added or removed from genes in virus-infected bees.
The team found that viral infections do change the pattern of DNA methylation in honey bees, and in a completely different set of genes from the ones in the RNAi pathway. Many of these differentially methylated genes are also involved in anti-viral responses in mammals, but they have not previously been linked to anti-viral responses in insects, said Grozinger.
“We found that there was very little overlap between differentially expressed and differentially methylated genes, suggesting dual genomic response pathways to viral infection,” said Galbraith. “For the first time, we characterized both the global gene expression and DNA methylation patterns associated with acute viral infection in honey bees. We confirmed that the RNAi pathway, which has been seen in other insects, is also an antiviral defense mechanism in honey bees. And, for the first time, we observed alterations in DNA methylation patterns in response to viral infection in honey bees.”
Honey bees with roots in the local environment manage much better in the struggle for survival than imported honey bees from foreign environments.
A world without bees would be a whole lot poorer – literally. In Denmark alone, an additional 600 million to 1 billion Danish kroner are earned annually due to the work done by bees making honey and pollinating a wide range of crops from apples to cherries and clover.
Unfortunately, bees all over the world are under pressure from pesticides, mites, viruses, bacteria, fungi, and environmental changes, among other things. The problems often lead to the syndrome of Colony Collapse Disorder, which can cause whole bee colonies to fall apart.
Scientists from, among others, Aarhus University, have now found that bees that are adapted to the local environment fare much better with regard to meeting the challenges than bees that have been purchased and imported from a completely different home area. The scientists determined this by investigating the interaction between the genetic makeup of honey bees and their environment. Even though quite a lot is known about the geographical and genetic diversity of honey bees, knowledge of how honey bees adapt to the local environment has been limited until now.
“Many beekeepers believe that it is best to buy queens from outside instead of using the queens they have in their own beehives. However, there is increasing evidence that the global honey bee trade has detrimental effects, including the spread of new diseases and pests,” says senior scientist Per Kryger from the Department of Agroecology at Aarhus University.
Local or exotic queen?
Productivity in beehives is typically measured by how much honey the bees produce. The desire to maximize earnings by importing bees changes natural genetic diversity. The question is whether commercial honey bee strains are actually more productive, all things considered. There is not much point in having a highly productive strain if it succumbs to Colony Collapse Disorder.
The studies were carried out in 621 colonies of honey bees with 16 different genetic origins. The beehives were set up in 11 countries in Europe. There were one local strain and two foreign strains of honey bees at each of the locations.
The factors that had the greatest influence on the survival of the bees were infection with varroa mites, problems with the queen, and infection with the disease nosema. Colonies with queens from the local environment managed on average 83 days more than colonies with queens from foreign areas.
“It is very clear that the local bees fare better than imported ones and that they live longer. It is not possible to point at one single factor that gives the local bees the advantage, but it appears to be an interaction between several factors,” says Per Kryger and continues:
“Our results indicate that the way forward is to strengthen the breeding programs with local honey bees instead of imported queens. That would help maintain the bee population’s natural diversity. It would also contribute to preventing the collapse of bee colonies, optimize sustainable productivity, and make it possible to maintain continual adaptation to environmental changes.”
The results of the project regarding the interaction between the genetic makeup of bees and their environment have been published in a special issue of the Journal of Apicultural Research, which is published by the International Bee Research Association.