There’s due concern about the fact that bumble bees are dying in the United States as well as other parts of the world. Researchers are baffled by the phenomenon because there seems to be no clear evidence which explains why the population of bumble bees is declining. In the commercial sense, bumble bees in the United States pollinate approximately 15 percent of all crops, which translates to about $3 billion dollars annually. Let’s take a closer look at this mysterious phenomenon.
Over the past 10 to 15 years, four species of bumble bees have been found to suffer alarming population declines of up to 96 percent. These species are Bombus affinis, Bombus occidentalis, Bombus pensylvanicus, and Bombus terricola. According to University of Illinois entomologist Sydney A. Cameron, the geographic range of these species has also declined by about 23 to 87 percent. Some other declining species include the Bombus franklini, Bombus fervidus, Bombus sonorus, and Bombus californicus.
To learn more about bumble bees, it’s necessary to know about their life cycle. Towards the end of autumn, the mated young queen bees search for a safe place to hibernate. The hibernation period extends into spring until the arrival of early warm days. The queens buzz around budding bulbs and flowers to find nectar and pollen, which is turned into honey to be fed to the hatching brood. At this time, the queen will also search for a place to build a nest. The queen begins a new nest by laying eggs into a ball of pollen and wax. After the eggs hatch, the queen adds to the nest while the grubs grow to become worker bees. The worker bees help to build the nest as the queen stays in the nest to lay more eggs. Once summer arrives, the queen lays eggs which would become the next cycle’s queen bees and drones. After mating with the future queens, the drones fly off, leaving the future queens in the mother colony. Towards the end of autumn, the old queen, the drones, and the worker bees would die, leaving the mated young queen bees to hibernate, and begin another cycle.
Some of the known threats to bumble bee populations include climate change, invasive species, habitat destruction, pollution, pesticides, and most significantly, the spread of diseases and pests through the commercial rearing of bumble bees. It’s hypothesized that the shipping of Bombus occidentalis and Bombus impatiens queens to European rearing facilities from 1992 to 1994 resulted in the acquisition of the microsporidian Nosema bombi, a virulent strain common in the European Bombus terrestris. The Nosema bombi fungus was found in a high number of the threatened bumble bee species. Research findings on the DNA of these species revealed that the bees have low genetic diversity which makes them more vulnerable to environmental pressures and other pathogens.