Parasites and pathogens that devastate honey bees in Europe, Asia, and the United States are spreading across East Africa, but don’t appear to be depleting native honey bee populations yet, researchers say.
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,” says Elliud Muli, senior lecturer in the biological sciences department at South Eastern Kenya University, and a researcher at the International Centre of Insect Physiology and Ecology in Kenya.
Researchers first discovered Varroa mites in Kenya in 2009. The new study, published in PLOS ONE, also provides baseline data for future analyses of possible threats to African honey bee populations.
“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,” says Christina Grozinger, professor of entomology at Penn State and director of the Center for Pollinator Research.
“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.”
Lions, elephants, and honey bees
Not only are flowering plants important for honey bees, but the insects are important for plants as well, says Harland Patch, research scientist in entomology.
“Honey bees are pollinators of untold numbers of plants in every ecosystem on the African continent,” Patch says. “They pollinate many food crops as well as those important for economic development, and their products, like honey and wax, are vital to the livelihood of many families. People say the greatest animal in Africa is the lion or the elephant, but honey bees are more essential, and their decline would have profound impacts across the continent.”
In 2010, 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, 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,” Grozinger says.
Varroa mites are present throughout Kenya, except in the remote north. In addition, Varroa numbers increase with elevation, suggesting that environmental factors may play a role in honey bee host-parasite interactions. Most importantly, 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 species, but, like Varroa, these species were absent from northern Kenya. The number of viruses present was positively correlated with Varroa levels, but was not related to colony size.
“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,” Patch says. “We suspect the seemingly greater tolerance of African bees to these pests over the western bees is a combination of genes and environment.”
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.
Parasites and pathogens
“This research is important because it confirms the resilience of African bees despite the heavy presence of recently introduced Varroa mites, and it suggests that the approach to manage these pests should not follow the application of pesticides as has been done in the western world,” Muli says.
These newly introduced pests to Africa might have long-term implications for the honey bee populations.
“As these new parasites and pathogens become more widespread, as pesticide use increases and as landscape degradation increases due to increased urbanization, farming and climate change, we expect to see the combination of all these factors negatively impact the bees in the future,” Grozinger says.
A USDA grant and a Basic Research to Enable Agricultural Development (BREAD) grant from the National Science Foundation supported the research.
Source: Penn State