How do I prevent beehives from returning

"Social Distancing" in the beehive

Manipulated by the virus: How ingenious viruses ensure their transmission, researchers have now uncovered in honey bees. Accordingly, the bees practice social distancing towards infected conspecifics within the hive. But at the entrance to someone else's beehive, workers infected by the virus are even fed instead of turned away. This makes it easier for the virus to jump from one colony of bees to the next.

Not only we humans are plagued by viruses - the same applies to honey bees. Not only do they suffer from the blood-sucking varroa mite, this parasite is also the carrier of several bee viruses. In addition to the deadly deformed wing virus, these include the Israeli Acute Paralysis Virus (IAPV), which could have played a decisive role in the death of colonies in the USA.

How do bees react to infected conspecifics?

However, how these viruses get from one beehive to another and whether the infection affects the behavior of infected bees was previously unknown. Amy Geffre of Iowa State University in Ames and her colleagues have now examined this in more detail. To do this, they used an automated system with which they could continuously track and evaluate the movements and behavior of more than 900 individually marked honey bees in three beehives.

In the first experiment, the researchers wanted to know how the honey bees within a hive react to a virus infection and to sick conspecifics. To do this, they each infected some colony members with IAPV. As a control, they also gave some other bees a DNA fragment that only triggers an immune response similar to that of an infection. How would the conspecifics of these bees react?

Avoiding contact in the floor

The observations revealed: The honeybees in the hive apparently immediately recognize whether a conspecific is infected or whether their immune system is running at full speed. The affected bees were still scanned intensively with the antennas, but the so-called trophallaxis - mutual feeding with liquid food - largely failed to materialize. The bees therefore practiced a kind of “social distancing” towards their infected conspecifics.

“We think that this reduction in trophallaxis is an adaptive social mechanism to reduce pathogen transmission through physical contact in the beehive,” say the researchers. This social distancing does not seem to be specific to an infection with IAPV, but apparently applies in general to infected or immune-activated conspecifics - this demonstrated the same avoidance response to the only immune-stimulated bees.

Guardian bees tricked

But as well as the honeybees within their hive seem well equipped to deal with infections, the IAPV virus still has a trick up its sleeve, as another experiment revealed. Here, the researchers placed some workers infected with IAPV in front of the entrance hole of a strange beehive. As a control, they also repeated this with healthy workers and with the immunostimulated bees.

The surprising result: As expected, only the healthy and immune-stimulated bees were recognized by the guards as foreign and chased away. But not the infected workers: "We found that the bees infected with IAPV experienced significantly less aggression," the researchers report. "At the same time, these bees caused more grooming and trophallaxis in the guards." Apparently the guard bees did not recognize these workers as strange and treated them more like a stick companion.

Manipulated smell

But why? "The infected bees somehow manage to bypass the defense reaction of the guards on the foreign hive," says co-author Adam Dolezal from the University of Illinois. “Something about them has to be different.” To find out what this is, the researchers analyzed the hydrocarbons present on the bees' carapace - fragrances that honey bees use to identify the hive and condition of their fellow bees, among other things.

And indeed: there were striking differences in eight of these connections. "The infection resulted in a molecular profile that differed from that of the controls and the immunostimulated bees," report Geffre and her team. "The virus apparently changes the smell of the bees." This could explain why the guards at the hive entrance reacted less aggressively to the infected workers than to healthy strangers: They smelled less strange.

Increased risk in many apiaries

But that means: the bee virus has manipulated its hosts in such a way that they promote its spread. Although the pathogen is slowed down within the beehives by social distancing, it can easily jump over to new colonies. "It is far more beneficial for a virus to be transferred to a new group of hosts," explains Dolezal. "And how do you do that? In the case of IAPV, you increase the chance that an infected bee from hive A will gain access to hive B. "

This finding is relevant on the one hand because it demonstrates once again that pathogens can also manipulate the behavior of their hosts. On the other hand, it also reveals possible problems with commercial beekeeping: "In modern beekeeping the beehives are often less than a meter apart," explain Geffre and her colleagues. In some orchards there are even hundreds of sticks at the time of flowering. This proximity can therefore make the transmission of dangerous viruses even easier. (Proceedings of the National Academy of Sciences, 2020; doi: 10.1073 / pnas.2002268117)

Source: University of Illinois at Urbana-Champaign

April 28, 2020

- Nadja Podbregar