Several parasites and pathogens that devastate honeybees in Europe, Asia, and the United States are spreading across East Africa, but do not appear to be impacting native honey bee populations at this time, according to an international team of researchers.
The invasive pests include including Nosema microsporidia and Varroa mites.
“Our East African honey bees appear to be resilient to these invasive pests, which suggests to us that the chemicals used to control pests in Europe, Asia, and the United States currently are not necessary in East Africa,” said Elliud Muli, senior lecturer in the Department of Biological Sciences, South Eastern Kenya University, and researcher at the International Centre of Insect Physiology and Ecology, Kenya.
“Kenyan beekeepers believe that bee populations have been experiencing declines in recent years, but our results suggest that the common causes for colony losses in the United States and Europe — parasites, pathogens, and pesticides — do not seem to be affecting Kenyan bees, at least not yet,” said Christina Grozinger, a professor of entomology and director of the Center for Pollinator Research at Penn State University. “Some of our preliminary data suggest that the loss of habitat and drought impacting flowering plants, from which the bees get all their food, may be the more important factor driving these declines.”
“The Africanized bees — the so-called “killer bees” — in the Americas seem to be having no problem with Varroa or diseases, so I would not be surprised to find they have some innate genetic tolerance to these pests,” said Harland Patch, a research scientist at Penn State. “We suspect the seemingly greater tolerance of African bees to these pests over the western bees is a combination of genes and environment.”
The team first discovered Varroa mites in Kenya in 2009. This new study, which was published in PLOS ONE, also provides baseline data for future analyses of possible threats to African honey bee populations.
In 2010, the researchers conducted a nationwide survey of 24 locations across Kenya to evaluate the numbers and sizes of honey bee colonies, assess the presence or absence of Varroa and Nosema parasites and viruses, and to identify and measure pesticide contaminants in hives and determine the genetic composition of the colonies.
“This is the first comprehensive survey of bee health in East Africa where we have examined diseases, genetics, and the environment to better understand what factors are most important in bee health in this region,” said Grozinger.
The researchers found that Varroa mites were present throughout Kenya, except in the remote north. In addition, Varroa numbers increased with elevation, suggesting that environmental factors may play a role in honey bee host-parasite interactions. Most importantly, the team found that while Varroa infestation dramatically reduces honey bee colony survival in the United States and Europe, in Kenya its presence alone does not appear to impact colony size.
The scientists found Nosema at three sites along the coast and one interior site. At all of the sites, they found only a small number of pesticides at low concentrations. Of the seven common honey bee viruses in the United States and Europe, the team only identified three, but, like Varroa, they were absent from northern Kenya. The number of viruses present was positively correlated with Varroa levels, but was not related to colony size.
Given their findings that African honey bees currently appear to be resilient to the effects of parasites and viruses, the researchers recommend that beekeepers in East Africa maintain healthy bee populations by protecting vital nesting habitat and the native flowering plant diversity that the bees depend on for food. In addition, the researchers suggest that beekeepers use pesticides sparingly.
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