Sunday, January 9, 2011

A dangerous sting for agriculture: climate change implicated in bee decline



The first in depth national study of wild bees in the US has established that several species have suffered a severe decline in population and range. Honey bees are important for commercial crop pollination of fruit, nut, vegetable and seed production in the United States, indeed globally.

"We have 50 species of bumble bees in North America. We've studied eight of them and four of these are significantly in trouble," said University of Illinois entomology professor Sydney Cameron, who led the study. "They could potentially recover; some of them might. But we only studied eight. This could be the tip of the iceberg," she said.


The three year study was recently published in the Proceedings of the National Academy of Sciences. It reported that the relative abundances of four of the eight species analyzed have declined by as much as 96 percent and that their surveyed geographic ranges have shrunk by 23 to 87 percent. Some of this decline has occurred in the last two decades.

Possible causes for the decline include climate change, habitat loss, low genetic diversity, and high infection rates with a parasitic pathogen, Crithidia bombi.

"Whether it's one of these or all of the above, we need to be aware of these declines," Cameron said. "It may be that the role that these four species play in pollinating plants could be taken up by other species of bumble bees. But if additional species begin to fall out due to things we're not aware of, we could be in trouble."

A study published in 2008 found that commercial bees from greenhouses often carry a harmful and highly contagious pathogen, Crithidia bombi. These bees regularly escape from greenhouses and interact with wild bees at flowers nearby. Near greenhouses, the rates of infection were up to one half of wild bumble bees were infected with C. bombi, whereas no bees harboured this pathogen at sites away from greenhouses. The frequency and severity of infections declined with increasing distance from greenhouses.

Another study published in March 2010 found high pesticide residues in bee pollen which may be a contributor to Colony Collapse Disorder (CCD) and declining bee health.

In a September 2010 media release a long term study of wild lily pollination in the Rocky Mountains of Colorado revealed a downward trend in pollination, while also pointing to climate change as a strong contributing factor.

"Bee numbers may have declined at our research site, but we suspect that a climate-driven mismatch between the times when flowers open and when bees emerge from hibernation is a more important factor," said James Thomson, a scientist with University of Toronto's Department of Ecology and Evolutionary Biology.

The 17 year examination of the wild lily in the Rocky Mountains of Colorado is one of the longest-term studies of pollination ever done. The study was published in Philosophical Transactions of the Royal Society B: Biological Sciences in September 2010.

Thomson compared the fruiting rate of un-manipulated flowers to that of flowers that are supplementally pollinated by hand three times each year. "Early in the year, when bumble bee queens are still hibernating, the fruiting rates are especially low," he says. "This is sobering because it suggests that pollination is vulnerable even in a relatively pristine environment that is free of pesticides and human disturbance but still subject to climate change."

A NASA study by Wayne Esaias and data from local apiarists in Maryland compared beehives seasonal weight gain from nectar flow with satellite imagery showing vegetation changes. "Each year, the nectar flow comes about a half-day earlier on average," said Esaias. "In total, since the 1970s, it has moved forward by about a month in Maryland."

While the growth of Washington as a major heat island was thought to be a factor, climate change was also mentioned as a likely contributing factor. "A month is a long time. If this keeps up, and the nectar flows continue to come earlier and earlier, there's a risk that pollinators could end up out of sync with the plant species that they've pollinated historically," Esaias said.



While honey bees are important for commercial crop pollination, there are many other pollinators active including bats and other small mammals, birds, wasps, butterflies, and countless other insects. The risk is that as we lose species diversity , major impacts will be felt on interspecies interdependence such as pollination.

May Berenbaum, an ecologist at the University of Illinois at Urbana-Champaign and lead author of a National Academy of Sciences published report in 2007 that highlighted the precarious status of pollinators in North America said "To borrow an old analogy that Paul Ehrlich often used, with the wild pollinators, losing a species is a bit like losing screws in a plane. If you lose a few here or there, it's not the end of the world, and your plane can still fly. But if you lose too many, at some point, the whole plane can suddenly come apart in mid-flight."

Scientists are only beginning to understand the ecological complexities and potential consequences when pollinators and the plants that rely on them start getting out of synchronisation in their life cycles that extinctions begin to occur. This is a major risk to commercial agriculture.


Sources:

* EurekAlert - University of Illinois at Urbana-Champaign, Jan 3, 2011 - Large-scale study reveals major decline in bumble bees in the US
* EurekAlert - University of Toronto, September 5, 2010 - Fears of a decline in bee pollination confirmed
* EurekAlert - University of Toronto, Jul 22, 2008 - Commercial bees spreading disease to wild pollinating bees - Plos One article - Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators?
* PLoS One, March 19, 2010 - High Levels of Miticides and Agrochemicals in North American Apiaries: Implications for Honey Bee Health
* NASA, August 25, 2009 - Honey Bees Turned Data Collectors Help Scientists Understand Climate Change
* US National Academy of Sciences - "The Birds and the Bees" - How Pollinators Help Maintain Healthy Ecosystems Testimony before the Subcommittee on Fisheries, Wildlife and Oceans Committee on Natural Resources U.S. House of Representatives, June 26, 2007.
* Photo of Bee on Tansy by Jenn Forman Orth Creative Commons CC BY-NC-SA 2.0 licence