Have you noticed fewer honeybees buzzing around
your garden this summer compared to previous
years? It's likely because more than 50 percent of honeybee
colonies kept by Wisconsin beekeepers died last winter. That figure
doesn't even take into account wild honeybees whose numbers are not tracked.
So what's causing the honeybee die-off?
Anette Phibbs, state apiarist with the Department of Agriculture, Trade and Consumer Protection, suggests there are several reasons. "A normal winter mortality rate is somewhere between 10-15 percent, but that number has been between 23 and 33 percent during milder winters, and around 40 to 45 percent during colder winters," Phibbs said.
This spring, many beekeepers reported losing bee
colonies to starvation. "During a cold
winter bees require more to eat, but don't move around the hive
to find the food they stored because it's too cold," Phibbs said. "The
lack of a mid-winter warm spell also prevented some
bees from taking cleansing flights, adding to
the disease pressure on the colony."
Another factor that contributed to the high winter mortality is varroa mite (Varroa destructor), which affects the honeybee brood. The parasitized brood usually dies, or young bees that survive emerge with deformed wings and a shorter life expectancy. Eventually the mite population grows so large the honeybee colony collapses.
The varroa mite originated in eastern Asia. Since the 1980s it has spread to most bee-keeping regions of the world, killing thousands of colonies. Its presence was first documented in Wisconsin in 1987. The varroa mite is most likely responsible for decimating most wild honeybee populations in the state.
Development of a miticide helped bring the
outbreak under control for a time. However,
in late 1997, a strain of varroa mite resistant to the control
treatment began killing more colonies. A new miticide was approved for
use in 1999. Recent apiary surveys show that honeybees treated with the new
miticide are largely free of varroa, while colonies not treated continue to
die in large numbers. The USDA Agricultural Research Service is working with
universities and honeybee queen breeders to develop honeybee stock that is
resistant to varroa mite.
Demand this spring for replacement honeybees from the southern U.S. outstripped the available supply because beekeepers in the northeastern U.S. also experienced a higher than usual winterkill. Wisconsin has thousands of hobbyist beekeepers, but many of their hives will remain silent.
Besides producing honey, honeybees are important
to agricultural producers as pollinators.
Bees transfer pollen from flower to flower, a critical step in
the production of many fruits and vegetables that adds millions of dollars
of value to Wisconsin-grown crops. Nationally, bee pollination adds $5-$20
billion to agricultural production. Under-pollinated crops are smaller
and less abundant, which could result in higher prices for consumers.
In 2000, Wisconsin's 84,000 commercial honeybee colonies produced 7,560,000 pounds of honey valued at $5,141,000, ranking Wisconsin among the top ten honey-producing states in the nation.
– Wisconsin Department of Agriculture, Trade and Consumer Protection Press Release, July 31, 2001. For more information contact Dave Litchy at (608) 224-5008 or (608) 212-3094.
