The deformed wing virus that is currently responsible for a major decline in the bee population has become so widespread due to human activities, such as trade and transportation, researchers have recently established.
The findings were presented in the journal Science on Friday, February 5, and were based on a study led by two British experts affiliated with the University of Exeter: Lena Bayer-Wilfert, senior lecturer in molecular evolution, and Roger Butlin, professor of evolutionary biology.
The scientists analyzed DNA sequences pertaining to the deformed wing virus and the varroa mite, which commonly transmits this pathogen to its new host.
Samples had been collected from 32 locations, across 17 nations, and this allowed study authors to determine exactly how the lethal mix became so prevalent throughout the world, regardless of geographic boundaries and natural barriers.
The source of the problem was traced back to the middle of the 20th century, when Asian honeybees were brought to the European continent, and ill-thought breeding occurred between these flying insects and European honeybees.
Asian honeybees had become accustomed to Varroa destructor mites found initially solely in Southeast Asia, knowing how to avoid these external parasites and to prevent them from sucking their blood.
Similarly, Western honeybees had been used to the deformed wing virus (DWV), a pathogen which normally remained on the surface of their bodies, causing little damage.
As explained by study co-author Lena Bayer-Wilfert, when the two bee species were brought together, both of them were negatively affected.
More precisely, Asian honeybees were introduced to the deformed wing virus; at the same time, their European counterparts became much more vulnerable to this pathogen, because mites contracted it and later transmitted it to their bloodstream.
As commercial trade caused Western honeybees to be brought to other parts of the world, such as various parts of Asia, Australia, New Zealand and the Americas, a local disruption turned into a devastating pandemic, because the deformed wing virus was carried by mites and caught by vulnerable bee populations that were completely unable to fend it off.
Due to the growing prevalence of varroa mite infestations, starting from 2006 it also became increasingly more common to identify cases of colony collapse disorder, an occurrence during which worker bees desert their hive, leaving the queen and all the immature bees and larvae unable to survive on their own.
That is how entire bee populations throughout North America have been severely depleted, and the same phenomenon has also been identified throughout Europe.
As study authors argue, if the spread of these pathogens had been triggered by natural factors, then it would’ve only occurred between adjoining territories.
Instead, it was possible to identify the same type of deformed wing virus in bee populations from Europe and New Zealand, likewise, and evidence of extensive transmission of the infection was also discovered between the European continent and Asia.
Consequently, it becomes obvious that the pathogen obtained such a wide geographical distribution thanks to human activities, such as bee transportation and trade.
Based on these findings, study authors point out that bee keepers should be more careful before moving colonies across borders, given that varroa infestations can prove deadly to such a wide variety of domestic pollinators, and even to their counterparts found in the wilderness.
The situation is further worsened by the fact that honeybees can easily transmit the deformed wing virus even in the absence of the varroa parasite, by leaving excrement and saliva on flowers that are then visited by bumblebees and other types of pollinators.
Therefore, unless stricter safety measures and screenings are imposed to prevent contamination triggered by human activities in the future, entire crops will be destroyed in the absence of pollinating bees, and the agricultural sector will be thrown completely off-balance.
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