Larson, who maintains 400 commercial hives and leases about 100 hives to Bay Area backyard gardeners, estimates about 20 percent of local commercial hives are lost annually to parasitic mites alone. The varroa destructor mite is the biggest culprit.
Another mysterious ailment that has grabbed headlines, colony collapse disorder, is a worldwide problem responsible for causing up to 35 percent of hive die-offs in some areas nationwide, he said.
The die-offs shouldn't be taken with a grain of sugar. Honeybees feed the nation, agriculturists say. One mouthful in three relies on honeybee pollination, according to the U.S. Department of Agriculture (USDA).
Larson said the Bay Area's long warm season helps bees, but that the climate also benefits the parasites. In winter, the queen bee lays fewer eggs, and bee deaths caused by the varroa mites can lead the hive to fail, he said.
Larson said the mites could be controlled with medications. But "it's a delicate process to try to kill a bug on a bug," he said.
Since he manages his hives organically, Larson dusts his bees with powdered sugar. "They clean each other off, so the mites will be chewed off and drop out of the hive," he said.
Fred Crowder, agricultural commissioner for San Mateo County, said in a recent crop report that colony collapse isn't a major player locally.
But beekeepers are wary since the cause of colony collapse is unknown. Worker bees in a colony abruptly disappear, leaving the queen and remaining bees with no ability to survive. The phenomenon began in 2006, when some beekeepers reported unusually high losses of 30 to 90 percent of their hives, according to the U.S. Environmental Protection Agency.
The USDA's preliminary data for winter 2009-10 has shown that collapse doesn't appear to be fading away, with the repeat collapse of some colonies.
As researchers search for a cause and cure, three possibilities are being considered: pesticides; a new parasite or virus; and stresses, including environmental, which could unexpectedly weaken colonies and compromise the bees' immune systems, according to the USDA.
Despite some news reports, cell phones and cell towers have not been implicated in throwing off bee homing systems, according to Stephan Kimmel, the author of a German study on the topic that discounted that claim.
But researchers might be getting closer to a connection between colony collapse and the varroa mite. A 2007 study found Israeli acute paralysis virus in 96 percent of bee samples with colony collapse, and the varroa mite could be transmitting the disease, according to the USDA. The virus was not found in non-colony-collapse samples, USDA researchers noted.
Scientists say while there is a strong correlation between the Israeli virus and colony collapse, they aren't ruling out that a complex of factors might be involved. And the 21st century is not the first time colony collapse-like phenomena have occurred. Several other honeybee disappearances occurred in the 1880s, the 1920s and the 1960s, according to the USDA.
Scientists are also trying to build a better bee to combat the new diseases. U.C. Davis bee breeder-geneticist Susan Cobey has been working with New World Carniolan bees, a darker honeybee, and is developing bee strains with high productivity, good over-wintering ability and disease resistance.
But the best action homeowners can take is not to use pesticides and especially not to use them at midday when the bees are most likely foraging for nectar, according to the Xerces Society, an invertebrate-conservation group. The organization recommends planting good nectar sources such as bee balm, anise hyssop, asters, basil, English lavender, rosemary and zinnias. Native plants are best for native bees.
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