Role Of Stress, Flower Loss In Bee Population Declines Investigated

Chuck Bednar for – Your Universe Online
The loss of wildflowers could be a bigger threat to bee populations than climate change, but stress management could help save these essential pollinators, according to the researchers behind a pair of recently-published studies.
Experts have long known that bees, and honeybees in particular, currently face a vast array of different threats, including pesticides and the parasitic Varroa mite. Now, a paper published Monday in the journal Trends in Parasitology have found that stress could be one of the primary causes of recent widespread losses in honeybee colonies in the northern hemisphere.
More specifically, the study authors report that a complex and mysterious interplay of different stresses and their impact on the health and immune systems of bees could be at fault. As a result, bees have grown weaker and have become more susceptible to diseases that insects can ordinarily carry without issue. The Italian researchers behind the study believe that stress management and improved nutrition could help rectify the situation.
Honeybees live in complex societies frequently characterized by densely packed populations, and as a result have developed unique mechanisms for interacting with pathogens, the researchers explained. However, pathogens such as Deformed Wing Virus (DWV) can cause asymptomatic infections normally contained by their immune systems, and stress factors can synergistically promote replication of the disease and symptomatic infections.
“These covert infections are very common all over the world and represent a kind of Damocle’s sword for honeybee colonies,” study author Francesco Nazzi of the University of Udine said in a statement. “When bees are exposed to stress agents, which may adversely affect the immune competence, a sudden health decay can occur due to uncontrolled pathogen proliferation.”
In their study, he and co-author Francesco Pennacchio of the University of Napoli call for more research into the molecular mechanisms driving the underlying immune responses of bees. They also suggest increased efforts to select bee populations that are more naturally resistant to these stresses, and by “enhancing the bee competence to face the challenge of environmental stress that may negatively influence immunity and health conditions.”
Another key factor that could be driving the decline of wild bee populations is the loss of pollen host plants, ecologist Dr. Jeroen Scheper of Wageningen University in The Netherlands and his fellow researchers wrote in a study published in Monday’s online early edition of the journal Proceedings of the National Academy of Sciences (PNAS).
“Growing concern about bee declines and associated loss of pollination services has increased the urgency to identify the underlying causes,” the authors wrote. “We assessed the relative importance of a range of proposed factors responsible for wild bee decline and show that loss of preferred host plant species is one of the main factors associated with the decline of bee populations in The Netherlands.”
According to Ars Technica reporter Diana Gitig, the basic concept behind the study is that wildflowers have been disappearing, and since bees rely on the nectar and pollen found in those flowers, it would only make sense that the loss of wildflowers would also result in the loss of bees. However, it has been a difficult idea to demonstrate.
“Different species of bees rely on different plants – the bee species that are disappearing have never been analyzed in terms of taste for the plants that are disappearing to see if they match up. And, once the bees or plants are gone, it’s hard to figure out what relationship (if any) they might have had,” she said. The new study, however, avoids this problem “by examining museum specimens of bees to figure out which bees like which flowers.”
Their efforts demonstrate that the bee species that have declined are those that prefer the pollen from the flower species that have also declined, Gitig added. Dr. Scheper’s team concluded that the loss of preferred host plants is actually one of the main factors that has driven the recent decline in wild bee populations, and it plays every bit as big a role as body size (in that larger bees require more food and are more sensitive to its loss).
How big of a problem is wildflower loss? As the Daily Mail reported on Tuesday, an estimated 97 percent of the UK’s flower-rich grassland has been lost since the 1930s, and two types of bees, Cullem’s bumblebee (Bombus cullumanus) and the short-haired bumblebee (Bombus subterraneus), have become extinct since the start of the 21st century.
“Based on these results, enhancing floral resources may be a good strategy for mitigating bee loss,” said Gitig. “Conservationists just need to figure out which bees they want to save, and they can increase the proper host plant species.”
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