A new study conducted by researchers at Iowa State University and the University of Illinois suggests that a deadly virus attacking honeybees alters their behavior and physiology in ways that boost the virus’s ability to spread.

The research, reported in the current issue of Proceedings of the National Academy of Sciences, found the Israeli acute paralysis virus (IAPV) seems to change bee behavior in ways that overcome some of bees’ natural defenses against disease pathogens, the announcement said.

“This research expands our understanding of how a disease can evolve rapidly to take advantage of changing conditions. In this case, the high-density placement of hives used in many areas to pollinate agricultural crops appears to make bees more susceptible to infection,” Iowa State professor of ecology, evolution and organismal biology Amy Toth said.

Toth was part of the study’s collaborative research team that included University of Illinois entomology professor Adam Dolezal, one of the lead authors who performed the work while a postdoctoral researcher at Iowa State.

“Our research shows the IAPV infection increases the likelihood that infected bees are accepted by foreign colonies,” Dolezal said. “Somehow, it makes the infected bees better able to circumvent the guards of foreign, uninfected colonies.”

To capture the behavior of individual bees, researchers tagged each one with the equivalent of a tiny quick-response (QR) code and continuously monitored their interactions. The scientists were able to simultaneously track the behaviors of as many as 900 bees and used this automated system to study how IAPV infection might affect the bees’ social behavior, including trophallaxis, a process by which honeybees exchange regurgitated food and other liquids.

“Honeybees ‘trophallax,’ or share food with each other by mouth. In the process, they are transferring social signaling molecules that give their trophallaxis partner information about their home colony, social status and health, among other things,” said Amy Geffre, the other lead co-author of the study who conducted much of the direct observation of the bees while a master’s student in ecology, evolution and organismal biology at Iowa State. “Trophallaxis is an important behavior to consider in these studies, as current research indicates that many diseases can be transmitted through saliva, particularly during food sharing.”

Geffre studied the bees in a lab environment and apiary settings. “In both cases, we found the infected bees changed their behavior and social signals dramatically,” she said.

In their own hives, IAPV-infected bees — and bees that had had their immune systems stimulated to mimic infection — engaged in less trophallaxis than their healthy counterparts. This type of “social distancing” response is well known in bees and is thought to protect hive-mates from getting infected with the disease.

Conversely, when the scientists placed honeybee workers in cages with guard bees from foreign colonies, the infected bees engaged in more trophallaxis with the guard bees. Also, when infected bees were placed at the entrance of foreign hives, the guards were twice as likely to admit them than to let in healthy bees or bees whose immune systems had been stimulated. The changed behavior seemed to be specific to the IAPV infection, which meant something about the infected bees must be different.

“The virus seems to change how the bees smell. The infected bees also may be behaving in a way meant to appease the guards from non-infected hives by trophallaxing more,” Dolezal said.

“Our findings suggest that the IAPV virus has been able to manipulate the behavior of its host to increase transmission between hives,” Toth said. “This is happening in ways that may not have been possible without novel, human-created environments in modern agriculture.

“Bee health is a huge challenge right now,” she said. “One practical implication of this research is to suggest that spacing colonies farther apart might help fight spread of the IAPV virus or other diseases within an apiary.”