Plant Compound Helps Virus-Infected Honey Bees Find Their Way Home

A plant-derived compound helps bees beset by a colony-ravaging virus overcome the cognitive effects of infection and navigate their way home, suggests a new study. 

The widespread death of honey bee populations around the globe has caused great concern to scientists and environmental groups. The most common honey bee, the western honey bee (Apis mellifera) is a vitally important pollinator. But bee hives have been beset in recent years by deadly events, such as colony collapse disorder (CCD), where large numbers of worker bees in a colony simply disappear.

Bee GPS inhibited by mite virus

The causes of CCD remain a mystery. Researchers believe that pesticides, environmental factors and diseases may all play a role. One major cause of honey bee illness is the aptly named Varroa destructor mite. This parasite harbors and spreads a virus called the deformed wing virus (DWV). In bees with high viral loads, replication of the virus during development leads to deformed and wrinkled wings post-metamorphosis. Reduced nutrient uptake due to the virus is thought to be a key factor in the mass death of bees. Additionally, impacts to infected bees’ ability to fly and navigate to and from their colony is a potential contributing factor in the disappearance of so many foraging bees.

Unfortunately, the steps that beekeepers might normally take to suppress such mites, such as the use of pesticides, have other significant environmental drawbacks. Bees are in desperate need of a solution.

Researchers at National Taiwan University, publishing in the journal iScience, have taken a new tack to battling this bee-bruising virus. Instead of trying to suppress the virus, what if we could simply make the bees more resistant to its effects?

Making a bee virus-resistant 

The researchers, including senior author Yueh-Lung Wu, investigated a plant-derived compound called sodium butyrate (NaB). NaB is part of a class of chemicals called histone deacetylase inhibitors. When genes encoded in DNA are being transcribed into RNA to enable the production of proteins, histone deacetylation is a chemical conversion that stops the transcription process. NaB and related compounds essentially keep the transcription party going, increasing the level of gene expression. An earlier study by the same team showed that dietary NaB could boost honey bees’ expression of genes related to immunity and learning and memory. Could it also provide them with a resistance to DWV?

The team fed honey bees with either a regular diet or one laced with NaB, and then infected a proportion of each group of bees with DWV. In the researchers’ lab setting, 90% of DWV bees had died within five days of infection. However, addition of NaB to the bees’ diet resulted in more than 90% of infected bees surviving five days post-infection.

“Our findings show that feeding the insects with NaB before virus exposure can counteract the negative impacts of the pathogen,” Wu commented in a press release. “We also found previously that NaB can upregulate some immune response genes in bees, and this can help suppress viral replication and improve bees’ chances at survival.”

The team analyzed gene expression with and without NaB dosing and showed the compound produced gene expression changes across several processes, including learning and memory. 

Tracked hives reveal improvements to bee navigation

The next step was to determine whether these genetic changes could be improving bees’ ability to find their way home from a forage. To do so, the researchers wired up the entrances to several hives, each containing more than 10,000 bees, with tracking technology that was able to determine how bees exited and returned to the hive. Over a 30-day period after infection, infected hives supplemented with NaB were able to maintain their return rate, whereas hives without NaB had higher rates of lost bees. Over the course of the 30-day experiment, the virally infected hives lost 1.53 times as many bees as the infected hive fed NaB.

The findings are potentially exciting for beekeepers, as NaB could be an easy-to-use supplement to protect vulnerable bee populations. “Sodium butyrate is really cheap. So, if we can prove its benefits, it would be an easy and affordable approach for beekeepers to keep their bees alive,” Wu concluded

Reference:

Tang, CK, Lin, Y, Jiang, J, et al. Real-time monitoring of deformed wing virus infected bee foraging behavior following histone deacetylase inhibitor treatment. iScience. 2021: 103056. doi: 10.1016/j.isci.2021.103056