There have been a number of interesting research papers about bees that have been published over the past few months. Scientific teams around the world have been exploring the bacteria that live in bees’ digestive systems, the chemicals that bee feet secrete, and the detailed impacts of neonicotinoid pesticides on both honey bees and bumblebees. Let’s first sketch out some general features and functions of bees and then fill in our outline with some of the interesting new observations.
There are 20,000 known species of bees around the world. Most of these bee species live solitary lives, but a small number of them form large, highly complex societies. These social behaviors have arisen several times during the evolutionary history of bees and can result in colonies of several dozen to many thousands of individuals. True social bees (the “eusocial” bees) have cooperative reproduction, specialized divisions of labor (“castes”), and a single reproductive individual (the Queen). Bees consume the sugary secretions made by flowering plants (“nectar”). Flowers produce nectar to attract bees (and other organisms) so that pollen (which contains the flowers’ sperm) can be distributed to other flowers to fertilize their ova. Some bees also collect the protein-rich pollen and use it to feed their larvae. One group of bees (called the “corbiculate” bees) have specialized sacks on their back legs called “pollen baskets” that help to make the gathering and transport of pollen more efficient. Honey bees, bumblebees, and stingless bees are all eusocial, corbiculate bees.
Picture the economy of a honeybee hive: worker (“forager”) bees find flowers and gather nectar and pollen. They use their mouthparts to lap up the nectar (a watery solution of mostly sucrose) and store it in their “nectar stomach” (or “nectar pouch”). Laden down with up to half of their body weight in nectar, the foragers then fly back to the hive, brush off their pollen load, and transfer their nectar into the mouths of other worker bees (“hive bees”). The hive bees then continue to transfer (mouth to mouth) the nectar through a sequence of hive bees. With each transfer the nectar become less and less watery, and it is chemically altered via series of enzymes that are produced by the salivary glands of the bees and also by the bees’ microbiome bacteria. The warm temperatures of the hive and the collective wing flutterings of the hive bees further accelerates the water evaporation from the transforming nectar. This new substance, which is more concentrated than the original nectar and also more stable and resistant to bacterial decay, is honey. Honey is the stored food for the hive to help it survive through the winter. Honey is also mixed with pollen to make “bee bread” which is used to feed the bee larvae.
A research paper published in Science Advances (March 29, 2017) by a team of scientists from the University of Texas at Austin looked at the bacterial components of social, corbiculate bee species’ gut microbiomes. They found that evolutionary lines of these bees maintained a similar core of bacteria in their microbiomes even if they had been separated from each other for many millions of years. They also found that these evolutionary microbiome similarities were unchanged in populations even if they lived great geographical distances apart! The social nature of these bee species and the intra-hive overlapping of many generations insures a continuity of microbiome inheritance. Possibly the conservative influence of the social environment on the bees’ microbiome flora is another significant evolutionary benefit of social behavior! It will be interesting to look at the specific microorganisms that make up this common core of the bee microbiome to determine their roles in bee metabolism, behavior or in the synthesis of honey.
In another study, a research group at the University of Bristol looked at the chemicals synthesized by glands in the feet of bumblebees. Their paper (published in Scientific Reports on March 7, 2017) observed that bumblebees visiting a flower to collect pollen and nectar leave a unique chemical footprint behind. These footprints can be interpreted by other bumblebees to recognize flowers that have been visited by their hive mates and also to recognize flowers that have been visited by bumblebees from other hives. This information helps the bumblebees to avoid competition with each other and also to avoid flowers that have been drained of nectar. The bumblebees can also use the rate of chemical changes that occur in these footprints as clocks to time when the last flower visit occurred (and calculate if there has been sufficient time for the flower to regenerate a harvestable volume of new nectar!).
There were three important papers about the effects of neonicotinoid pesticides on bees. The first, by a research team from the Royal Holloway University in London and the University of Guelf in Canada (published in Proceedings of the Royal Society B, May 3, 2017), showed that exposure to thiamethoxan (a neonicotinoid pesticide) inhibited ovary development in Queen bumblebees. The second, by a group from the University of California, San Diego, showed that thiamethoxan interfered with the ability of honey bees to fly (thus reducing their ability to gather nectar and pollen and inhibiting their ability to make overwintering food stores). These two, relatively small studies corroborated an extremely ambitious, multinational study conducted in Europe that looked into the field impacts of neonicotinoid pesticides on honey bees and bumblebees (published in Science, June 29, 2017). This field study showed that honey bees exposed to neonicotinoids have lower survival rates in the winter and that bumblebees similarly exposed have greatly reduced reproductive rates. These data match the observations of the two previous studies perfectly. This study also measured levels of neonicotinoids in a wide range of bee species and bee environments and determined that previous laboratory studies were using very appropriate levels of pesticides in their experimental designs. This study further observed that the water-soluble neonicotinoids were found well outside of their active spray areas suggesting that the chemicals were moving in soil and surface water.
So, our wonderful bees with their established microbiomes have distinctively smelly feet! We now very precisely know the harmful connection of neonicotinoid pesticides on these vital pollinators. Europe has banned the use of neonicotinoid pesticides and hopefully the United States will do the same.
And finally, a paper published two weeks ago (July 17, 2017) in the Proceedings of the Royal Society B indicated that 30% of bumblebee species worldwide are showing significant decreases in numbers. Climate change and parasitic infections are the two likely forces triggering these declines. Bumblebee species with small geographic ranges, narrow climatological tolerances and no evolutionary history of or defenses against parasites are the populations that have decline the most.
Bees need our help, everyone, or at least our consideration!
More next week!