A new study published in the journal Proceedings of the National Academy of Sciences has found that honey bees carrying the deadly Israeli acute paralysis virus (IAPV) are twice as likely to be allowed access into foreign bee hives compared to healthy invaders. The findings suggest that the IAPV infection alters the behavior of infected bees making it easier for the virus to spread in healthy hives.
The researchers were able to study the behavior of 900 individual bees by tagging them and observing how often they engaged in trophallaxis – a process whereby honey bees feed hungry workers by exchanging regurgitated fluids. Yikes. They put 90 to 150 labeled bees that had been exposed to the virus into a colony and after five days found that the healthy bees were already refusing to feed the infected bees. The sick actually moved around more than healthy bees, likely in the desperate pursuit of a meal, but 50 percent less trophallaxis was seen among the sick bees.
The response is an example of how bees try to suppress infection within the hive by shunning those carrying illness and isn’t specific to IAPV. Healthy bees whose immune systems had been stimulated to indicate infection were also shunned by their hive mates.
Things changed however when the researchers placed the infected and “sick” bees at the entrance of a foreign hive. The bees with stimulated immune systems, who weren’t carrying the deadly IAPV, were actually less likely to be admitted to the hive compared to the infected, as they continued to disengage in trophallaxis, alerting the guard bees to their ill health. The researchers observed that those carrying IAPV were twice as likely to be granted access to the healthy hive.
They realized something about the IAPV bees must be different, and tested to see if they were giving off some kind of chemical signal to trick the bees guarding the healthy hive into letting them in. An analysis of the chemistry of the hydrocarbons that coat the bees' exoskeletons revealed that there were distinct hydrocarbon profiles for the IAPV, immune stimulated and healthy bees. The discovery indicated that IAPV is evolving in a way to enhance the carrier’s ability to break into healthy hives and spread the illness.
The above video shows two honey bees (center) engaging in trophallaxis as a way of feeding workers. Healthy bees avoid feeding their sick hive mates to stop the spread of illness is a hive.
"The most important finding of our study is that IAPV infection increases the likelihood that infected bees are accepted by foreign colonies," said Adam Dolezal, a professor of entomology at the University of Illinois at Urbana-Champaign who led the new research, in a statement. "If you're a virus, it's much more valuable to get transmitted to a new family group, like traveling from one city to a new city," he said. "And so how do you get there? You increase the chances that the sick bees leaving colony A are more likely to get into colony B."
The findings paint a worrying picture for the future of honey bees, whose numbers are already in decline, in the face of this duplicitous virus.