Hygienic Bees Smell Disease and Do Something About It
How Hygienic Behavior in Honey Bees Influences Colony Health
Reading Time: 4 minutes
In a honey bee colony, thousands of individuals are in close physical contact as they feed and groom each other. While the hive is generally quite clean (bees leave the hive to defecate and to die), it’s still a pretty great environment for diseases and parasites to proliferate. As warm and crowded with babies as a preschool classroom, the brood nest can host diseases such as American foulbrood and chalkbrood, or pests like the Varroa destructor mite.
Honey bees have two categories of response to health threats: individual immune responses, and group, or “social,” immune responses. An individual immune response is the activation of a bee’s own tiny immune system. Social immune responses are behaviors that contribute to overall colony health, sometimes at the expense of the individual bee.
One form of social immunity is called hygienic behavior, wherein many young workers resist the spread of pathogens and varroa mites by detecting, uncapping, and removing unhealthy brood.
The colony loses some individual larvae, but is able to control or even eliminate chalkbrood and American Foulbrood; hygienic behavior can also keep varroa mite reproduction at livably low levels.
Why Don’t All Bees Exhibit Hygienic Behavior?
Hygienic behavior is a genetic trait, meaning it is heritable. But because genes involved in its expression are recessive; and because each queen mates with many drones, hygienic behavior must be persistently selected for over time.
The way hygienic behavior works is truly complicated: The top scientists and breeders of hygienic bees are still trying to understand the nitty-gritty details, such as how many genes are involved in producing this trait, and what scent or scents, exactly, trigger hygienic bees to detect, uncap, and remove infected or infested brood.
But don’t despair. You don’t really have to understand polygenic traits to get the gist of hygienic behavior and how it can support your own bees’ fight against pathogens and pests.
The hygienic behavior trait is found in all stocks and races of bees. Just like any trait, such as gentleness or small brood nest size, beekeepers can select for hygienic behavior by testing for the trait and using the queens they find to be most hygienic to raise daughter queens.
Testing for hygienic behavior requires patience, as does selecting for it; it can take years of close observation and selection choices before your stock becomes really hygienic. Unless a bee breeder is artificially inseminating her queens, she will also need to be making sure she’s got plenty of hygienic drones near her mating yards (remember, this trait is recessive and therefore requires the father’s hygienic input).
Famous Hygienic Bee Lines
I’ll go over just a few rather famous hygienic lines, while emphasizing that any bee breeder can select for hygienic behavior, and should.
Brown Hygienic bees: Dr. Rothenbuhler coined the term “hygienic behavior” in the 1960s, specifically to describe particular bees’ response to American foulbrood: he noticed that some bees would detect the disease in recently sealed brood, then uncap and remove that brood — all before this bacterial disease entered its contagious stage. The line of hygienic bees Dr. Rothenbuhler worked with back then was known as Brown Bees, and were very defensive. He was probably so excited to select for hygienic behavior, he forgot to select for niceness.
Minnesota Hygienic bees: speaking of “niceness,” Dr. Marla Spivak and Gary Reuter developed the now-famous Minnesota Hygienic line of bees in the 1990s. They used artificial insemination to ensure that the drones the breeder queens were mated with were also hygienic. Spivak distributed some queens to commercial beekeepers, who were able, by raising daughter queens, to make their overall operations pretty hygienic. Those commercial beekeepers then sold Minnesota Hygienic queens to other beekeepers across the country.
Spivak discontinued raising and inseminating her MN Hygienic queens in the late eighties, in part so that her stock didn’t diminish genetic diversity of honey bees by showing up in too many apiaries across the country. Dr. Spivak thought it made more sense for many beekeepers to actively select for hygienic behavior amongst their own stock than for everyone to purchase hygienic queens from a few genetic lines, which might or might not be suited to a particular beekeeper’s climate or operation’s goals.
Varroa Sensitive Hygiene, Baton Rouge: A specific type, or aspect, of hygienic behavior in bees is referred to as Varroa Sensitive Hygiene (VSH). VSH bees were first developed at the USDA Bee Breeding Lab in Baton Rouge, Louisiana in the late 1990s. A team of researchers bred bees that were somehow keeping mite reproduction levels incredibly low, even while the colonies around them exploded with the pests. At the time, the researchers didn’t recognize these mite-suppressing bees as hygienic, so they named them Suppressed Mite Reproduction (SMR) bees.
Later studies revealed that SMR bees are in fact expressing hygienic behavior by detecting reproductive mites in a sealed pupa cell, then uncapping and removing that pupa before the mites have a chance to reproduce on their host. The SMR trait was renamed Varroa Sensitive Hygiene.
Now, you may notice that your own bees do a bit of uncapping here and there — a kind of snooping around behavior. Uncapping is the first step in hygienic behavior.
A worker makes a little hole in the top of a sealed cell to see (or rather smell) what’s going on. Sometimes other bees within the same colony patch up that cell with a bit of wax, not sensing that something might be wrong with it. Hygienic bees will go a step further and remove the abnormal pupa.
I hope you’re convinced that the hygienic trait is an important tool for your bees to have in their healthcare toolkit. But perhaps you only have one colony and are not in the business of raising your own queens. If this is the case, you can buy hygienic queens. You’ll need to get to know your local queen breeders, and, just like you’d inquire about race or disposition, ask if their queens have been selected for hygienic behavior before purchasing them. You want your bees to be excellent at fighting mites and diseases, which, let’s face it, aren’t going away. Why not help bees help themselves with hygienic behavior?