Honeybees Social Distance to Deal with Diseases
Honeybees have been “social distancing” for a very long time, as a matter of survival of the strongest.
Take the deadly acute paralysis virus (IAPV), for example. A scientific study indicates that when a beehive is infected with it, once a bee is ill, she is less likely to be fed or touched by her hive mates.
Bees are highly sensitive to infectious diseases, even more so than other insects. Not least of all because they live in very crowded conditions where there is a lot of physical touching. At the same time, bees are among the cleanest of insects, with high quality self-grooming and grooming of each other as well as a variety of hygienic behaviors for keeping the hive clean. Once sick larvae are detected they are removed from the hive immediately.
Scientists have speculated that the virus has found ways to spread to new hives by turning infected honeybees into carriers that pass by guards undetected. This speculation is based on the fact that sick bees seem to do a better job of getting past hive guards and entering new colonies than healthy bees do.
Not a lot has been known about how bees act when infected with viruses, so to find out, new research was carried out by Adam Dolezal, an insect physiologist who studies IAPV at the University of Illinois, Urbana-Champaign (UIUC) and UIUC computer scientist Tim Gernat, who developed an automated system to monitor bee behavior.
Dolezal wanted to find out whether IAPV had a way to sneak past colony defenses so the virus can successfully spread. Hive guards literally guard the hive and keep trespassers out. Their antennae detect an assortment of chemical signals on the outside of other bees, called cuticular hydrocarbons, that identify them as colony members or outsiders.
Here's a fine 2:10-minute video by DIYDad of how guard bees act when a robber bee tries to get into the hive:
Olav Rueppell, an evolutionary biologist at the University of North Carolina, Greensboro, ponders whether this could be an indication of a “coevolutionary arms race” between pathogens and social organisms. This points out potential dangers to placing commercial hives too close together.
The team trained the computer to identify a behavior called trophallaxis, where honeybees feed their hive workers by regurgitating food from a pouch called a crop. Hungry bees can usually convince other bees to give them some food.
The team also affixed labels to the backs of around 900 bees in three colonies and tracked them with a camera that took pictures every second. The computer mapped locations and orientations of all labeled bees.
Dolezal infected 90-150 labeled bees with IAPV and put them into each colony to see how they would react to the virus. Five days later, the team observed that the healthy bees were avoiding the infected bees. Only about half as much trophallaxis took place with sick bees as compared to healthy bees, no matter how hard the sick bees begged for food. Sick bees moved around a lot, probably looking for food.
These findings show how bee behavior in a real colony setting can suppress infection, according to Christina Grozinger, a behavioral ecologist at Pennsylvania State University, University Park, who was not involved in the project.
Dolezal and colleagues placed IAPV-infected bees outside another colony, and the guards allowed entry to about 30% of them, compared to only around 15% of healthy outsider bees. The research team is troubled by this higher amount of virus movement. Dolezal and his team’s report on this subject is in the Proceedings of the National Academy of Sciences.
It is unclear to researchers why IAPV is so successful at deceiving hive guards, but possibly it alters the abundance of various cuticular hydrocarbons, which differed between infected and uninfected groups. For instance, they found that IAPV infections had lower levels of octacosane, which is associated with greater acceptance by other bees. Sick bees were also more submissive when challenged by guards, and likelier to offer them food. These behaviors may also help spread the disease.
This is a big problem, but even worse is that IAPV isn’t the only illness these bees may carry. Varroa mite parasites, which have wiped out bee populations worldwide, can also carry IAPV and other deadly viruses. If IAPV helps other pathogens spread, this could be a huge problem for bees, especially those belonging to commercial beekeepers. They pack their hives tight for efficiency, so there isn’t much they could do to stop a virus infection spreading, according to Dolezal.
Here is an unrelated scientific study on IAPV for those who want to know more about this honeybee infection.
As humanity deals with social distancing and the Covid-19 pandemic, we are more sensitive to the plight of bees as they cope with many deadly infectious viruses and how they use social distancing as a behavior to protect the colony.
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