Study: Flowers can spread harmful bee parasites

Flowers can serve as platforms for parasites that can harm bees, a University of California-Riverside study has found.
Tim Hearden

Capital Press

Published on August 10, 2015 2:13PM

Courtesy of Kathy Keatley Garvey, UC-Davis
A honey bee forages on a pansy flower. A University of California-Riverside study found that flowers can be a platform for parasites that harm bees.

Courtesy of Kathy Keatley Garvey, UC-Davis A honey bee forages on a pansy flower. A University of California-Riverside study found that flowers can be a platform for parasites that harm bees.


Bees and flowers are made for each other in nature, but sometimes the tandem can be a fatal attraction for pollinators.

That’s because harmful or even deadly parasites can lay in wait on flowers for visiting bees, researchers at the University of California-Riverside say.

Parasites such as Nosema apis and Nosema ceranae are known to cause lethargy, dysentery, colony collapse and queen death in heavily infected bees, they said.

Contrary to popular belief, some parasites attack more than one type of bee, so different bees that forage on the same flower can transfer pests to different populations, said lead researcher Peter Graystock, a postdoctoral researcher in UCR’s Department of Entomology.

“Flowers can be visited by a complex web of pollinators and here we are increasingly finding that terms such as ‘honey bee parasite’ and ‘bumblebee parasite’ can be misleading in the grand scheme of the parasites’ transmission and dispersal dynamics,” Graystock told the Capital Press in an email.

“If parasite transmission and dispersal is frequently taking place at flowers, the potential for inter- and intra-species disease spillover is large,” he said.

The study, for which UC-Riverside researchers teamed with the University of Sussex in England and published results in the journal Proceedings of the Royal Society B, has ramifications for growers of almonds and other major agricultural commodities that rely on healthy bees for pollination.

When hives are moved around in orchards, beekeepers may also be inadvertently moving parasites, which could then be dispersed on flowers in the new area, Graystock said.

“This would potentially have a negative effect on local pollinators in that area,” he said. “In regards to the (commercial) flower industry, once plants have started to flower and be visited by bees, then these flowers could become sources of parasites, which if then transported to new location can then introduce or increase the prevalence of bee diseases.”

Graystock advises growers and beekeepers to be wary of introducing bees into areas they know have had unhealthy bees, and to avoid putting too many bees in an area and causing heavier traffic — and possibly heavier parasite transmission.

Growers can try to alleviate the problem by keeping a diverse array of flowers on their land to avoid periods of flower shortage, he said. Beekeepers should regularly screen their bees for parasites and avoid moving diseased bees, he said.

The latest study comes as scientists are searching for causes of colony collapse disorder, which has led to over-winter colony losses averaging 30 percent for the last eight years and as much as 50 percent losses in the last two years, according to the USDA-supported Bee Informed Partnership.

While some environmentalists have been quick to blame pesticides for the die-offs, researchers have cited many other contributing factors.

Eric Mussen, a retired UC-Davis extension apicurist who helped the Almond Board of California develop a best-practices manual last year, said that scientists are just beginning to identify the many microbes that come in contact with bees and that some are actually beneficial to bees.

As honey bees have been in North America for nearly 400 years, their microbes are likely well spread nationwide, Mussen said in an email. Even the “exotic” honey bee diseases like Nosema ceranae and Israeli Acute Paralysis Virus moved through the nation’s colonies quickly and are now nearly ubiquitous, he said.

To totally isolate his or her bees from these microbes, a beekeeper would need to determine whether the microbes are already in the bees and, if not, find an area to move into where there are no feral or managed colonies of honey bees within a 50-mile radius, Mussen said.

“Any beekeeper can avoid commercial pollination, if there is a fear of contamination of his or her colonies, but that fear is not apt to change the management patterns of most commercial beekeepers,” he said.

However, moving bees that are obviously diseased but being kept alive with good apicultural husbandry may spread the disease to wild bees that aren’t being cared for, Graystock said.

Most of all, growers should realize that the honey bees pollinating their crops are among some 20,000 bee species that all interact, the researchers say.

“Keep open-minded about ‘bee health’ and don’t simply focus on ‘honey bee health,’” Graystock said. “All are connected, at least by the flowers they all share.”



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