Signs of Fall 9: Bees!

Photo by H. Hillewaert. Wikimedia Commons

(Click on the following link to listen to an audio version of this blog … Bees!

At last count, since 2006, I written 27 blogs about bees. They are by far the most frequent subject of my short essays. There are a number of reasons for this: 1. Bees are almost everyone’s favorite insect. They are, to quote a bee researcher whose name is lost in the haze of the past, “the pandas of the insect world.” 2. Bees, including domesticated species and wild species, pollinate almost all of the wild and cultivated plants on Earth and are critical for a large percentage of our food production! 3. Many bees live in complex social groups and have very sophisticated forms of communication and control. And, finally, 4. Bee populations all around the world are in trouble, and their declining numbers and shrinking distributions are primarily due to human activity!

In an attempt to get a world-wide view of the well documented local decline and extinction of bees, two scientists in Argentina, Eduardo Zaltara and Marcelo Aizen (both at the Argentinian National Scientific and Technical Research Council), utilized the vast database of the Global Biodiversity Information Facility to explore the changes in the status of wild and domesticated bee populations over the time period of 1900 to 2018. The Global Biodiversity Information Facility in its role to monitor the distribution data of the plant, animal, microbial and fungal species of the world, amasses information on insect specimens in museum holdings, private collection inventories and community-based collection studies. Digging through this database, Zaltara and Aizen found, to their shock, that the number of bee species had declined globally by 25% since 1990! This sudden and precipitous drop in bee species over the past 30 years powerfully indicates that the world-wide-pollinator-web upon which we depend for almost all of our food, is in great peril!

Honeybee. Photo by C.J.Sharp, Wikimedia Commons

In another study, researchers at Penn State looked at populations of honey bees that had escaped the control and protection of their keepers. Honey bees are carefully managed “livestock” that are integrally important components of almost every aspect of plant-based agriculture. The influence of humans in creating and sustaining the modern honey bee has been significant. With all of the current problems with honey bees (viruses, mite ectoparasites, pesticide toxicities, colony collapse disorder, etc.) many bee keepers and bee biologists have expressed concern that the artificial, human-mediated selective forces that have created this organism may have also so weakened the species that it is now unable to thrive or maybe even survive in its current pesticide, pathogen and parasite-rich environment.

Honey bees, though, frequently escape from captivity and set up wild (“feral”) colonies that are then subject to all sorts of different (albeit, mostly “natural”) selection forces. The questions that were asked by the Penn State scientists were: 1. What were the winter survival rates of managed honey bee colonies versus feral honey bee colonies? Did all of the parasite control measures and virus treatments in the managed scheme increase survival during the incredibly stressful winter season? 2. What were the levels of three, important honey bee diseases (deformed wing virus (DWV)(a common cause of winter die-offs in honey bees), black queen virus (BQV) and Nosema cerane  (a very widespread, unicellular fungal parasite found inside of honey bee cells)? And 3. How actively were six genes known to be involved in honey bee immune systems expressed in the managed versus the feral colonies?

Honeybees, Public Domain, Pixabay

Twenty-five feral honey bee colonies were located across Pennsylvania and each was paired with a relatively nearby, managed honey bee hive. Over two years, the winter survival rate, pathogen/parasite levels and immunity gene activities were compared between the paired colonies. Results were published in Frontiers in Ecology and Evolution (January 13, 2021).

Winter survival of the managed and feral honey bee colonies were identical across the study. The implication here is clear: the feral colonies were either ridding themselves of disease-carrying mites through colony-wide hygienic behaviors (Varola mite levels in many of the feral colonies were actually lower than in the managed colonies), or the feral honey bees themselves through physiological (genetic) or other behavioral changes were resisting parasitism and also the spread of viral and fungal diseases as effectively as managed (and intensively treated) colonies.

Feral colonies did have higher levels of DWV, but the levels of this virus fluctuated in the these colonies much more than in the managed colonies. These data suggest that the feral honey bees were fighting against the spread or impact of the DWV physiologically, and the observation that the feral colonies had higher expression of five of the six immune-related genes substantiated this hypothesis. The higher levels of DWV in the feral colonies, though, also supports a widely held idea that feral bees can act as reservoirs for this extremely dangerous virus and may pass DWV to managed honey bee populations.

So, feral honey bees are able to deal with significant disease agents and parasites without human assistance. They may, though, be rich, local foci for these diseases which can then spread to managed hives.

Photo by I.Tsukuba, Flickr

Another research project on honey bees, conducted at Washington University in St. Louis, was published in Science Advances on October 14, 2020.  These experiments explored the generation of body scent molecules in honey bees that are used to recognize membership in a group.

Honey bees will, in times of nectar shortages, attack foreign honey bee hives in order to steal honey. These raids can result in significant loss of individuals in the immediate carnage of the attack but may also, more significantly, result in the decimation of the attacked hive if the raid leaves insufficient amounts of honey reserves behind to sustain the bees through the winter season. To prevent or at least discourage raiding, a hive will post guard bees at the hive entrances to monitor all of the individual bees going into or out of the hive. These guard bees rely on scent molecules contained in the waxy, waterproofing coating on the bee’s body to recognize members of their hive from non-members. These identity molecules are called “cuticular hydrocarbons” or “CHC’s”.

It was once assumed that CHC’s were genetically determined, and that the genetic homogeneity of the honey bees in a hive established the particular identifying scent for the individuals of the group. Experiments, however, in which very young (one day old) bees were successfully transferred from one hive to another threw some doubt on the accuracy of this genetic, CHC hypothesis. These transferred individuals of very different genetic makeups, successfully produce the group CHC’s that allowed them to enter and leave their new hive without interference.

Normal honey bee drone. Photo by Epgui, Wikimedia Commons

Examination of the gut microbiomes of bees switched from their “birth hives” to “foreign hives” (compared to controls that were raised in their birth hives) revealed 14 bacteria in different abundances or strains that differed significantly depending upon which hive a bee was raised. Six of these bacteria were similar among bees that grew up in a particular hive regardless of their genetics. None of these bacteria, though, were significantly associated with the individual bees’ birth hives.

These data suggest that an individual bee’s CHC’s may be generated genetically (this is likely the “birth hive” generated CHC identity similarity), but that a functional CHC may also be generated through modifications of the bee’s microbiome (this is likely the “raising hive” CHC identity similarity). These microbiome mediated identity compounds compared to the genetically determined CHC identity compounds may give populations of bees a more rapidly acting and, possibly, more flexible pathway to modify their behaviors in response to environmental changes affecting them.