Honey Bee Virus Tricks Hive Guards Into Admitting Sick Intruders
The virus tweaks bee behavior to infect new hives and may also spread other hive-killing pathogens and pests
Honey bees are known for running a tight ship. Their hexagonal honeycombs make the most mathematically efficient use of space for storing honey, they keep diseases from spreading by minimizing touching or feeding of sick hive-mates, and guards stationed at the hive entrance act as bouncers to keep out intruders.
But new research suggests a deadly virus tricks those normally vigilant guards into letting infected invaders into their hives, reports Erik Stokstad for Science.
“Somehow, the infected bees are able to circumvent the guards of foreign colonies, which they shouldn’t be able to do,” says Adam Dolezal, an entomologist at the University of Illinois and leader of the new research, in a statement.
The virus, called Israeli acute paralysis virus (IAPV), has also been shown to make forager bees more likely to get lost on their way home—upping their chances of spreading the virus to a neighboring hive.
By enabling these wandering bees to slip past an unfamiliar colony’s defenses, the virus has evolved a way to spread despite the sophisticated tactics bees deploy inside their colonies to tamp down infections.
"This is an interesting study that demonstrates an arms-race between a honey bee host and its viral pathogen at the behavioral level," Eyal Maori, a virologist at Cambridge University who was not involved in the research, tells Rosie McCall of Newsweek.
IAPV infections have been linked to colony losses and are one of many environmental stresses—including parasitic mites, pesticides, pollution and loss of plant diversity—making life more difficult for some of the insect world's hardest working farmhands. Without honey bees, roughly a third of the food eaten by Americans would disappear. Bees’ contributions to pollinating crops including apples, melons, cranberries, pumpkins, squash, broccoli and almonds are valued at more than $15 billion.
This new research suggests that the practice of stacking multiple hives next to each other in commercial beekeeping may play right into the hands of IAPV. Left to their own devices, bees tend to spread out, with just one or two hives per square mile.
Dolezal and his team wanted to study how IAPV spreads and had a hunch that it might make some strategic alterations to the behavior and physiology of infected bees. To track the insects’ behavior, the team tagged bees with barcode-like labels that could then be recognized and tracked by cameras attached to an automated computer system.
The system, capable of tracking up to 900 bees at once, was programmed to spot a behavior called trophallaxis, in which two bees smush their faces together while sharing regurgitated food and transmitting hormones or other chemical messages.
“Trophallaxis is essential to the spread of information and nutrition throughout the hive, but unfortunately, a behavior performed with such close social contact also allows viral infections to be transmitted through a hive,” says Gene Robinson, an entomologist at the University of Illinois and study co-author, in a statement.
The researchers used the automated system to track the behaviors of 90 to 150 IAPV-infected bees released into an experimental hive. The study found that bees infected with IAPV, as well as bees with stimulated immune systems designed to mimic infection, were shunned by their hivemates when they went looking for trophallaxis, the researchers report this week in the journal Proceedings of the National Academy of Sciences.
But the bees’ brand of social distancing inside the hive wasn’t enough to protect them from the virus. When the team placed individuals infected with IAPV outside a hive, the guards gave them special treatment—letting them in more often and engaging in more trophallaxis with them than with healthy or immune-stimulated bees.
The researchers suspect the guards’ sweet spot for the sick bees may be because of their smell, which is used by the guards to discern friend from foe. The researchers found that smelly compounds called hydrocarbons were chemically altered in bees infected with the virus. But these sick bees may slip past the velvet rope by simply being nicer to the guards, reports Science. The researchers observed sick bees being more submissive and sharing more food when approached by hostile guards.
The findings suggest that IAPV is evolving to infect as many hosts as possible, says Dolezal in a statement.
Other researchers say IAPV’s ability to modify the bees’ behavior to get from hive to hive might also increase the spread of additional threats. IAPV could aid the transmission of pathogens and pests, such as the varroa mite, to new colonies, Maori tells Newsweek. The mite feeds on bees’ fat reserves and has devastated colonies across the world.
More research is needed to determine if IAPV plays a big role in the spread of mites and other viruses, Maori tells Newsweek, which would represent a significant vulnerability in commercial beekeeping operations that keep many hives close together.