The honeybee population appears to have survived the winter in better shape than a year ago, but still faces several significant threats, a Purdue University honeybee specialist said.
After the brutally cold, wet winter of 2013-14 in much of the U.S., observers reported one of the largest bee die-offs ever recorded, with a mortality rate of about 65 percent for Indiana, said Greg Hunt, professor of entomology. Based on his primary investigation and discussions with beekeepers, Hunt estimated this year's losses at about 29 percent.
"It seems much better than the year before, even though it was another cold winter," Hunt said.
Honeybees are essential to agriculture because they pollinate food plants such as fruits, nuts and vegetables. According to the U.S. Department of Agriculture, honeybee pollination is worth about $15 billion a year in crop production.
But the honeybee population has been declining for years, with the U.S. losing about one-third of its hives annually, Hunt said. Experts estimate the number of honeybee colonies in the U.S. dropped from about 4 million in the 1970s to about 2.5 million now.
The reasons for the bees' decline aren't entirely clear, Hunt said, although there are likely a number of contributing factors.
Especially baffling is a phenomenon known as colony collapse disorder, when adult worker bees disappear from their hives for no apparent reason, leaving the immature bees in the colony to starve.
"Although colony collapse disorder has generated a lot of attention, symptoms haven't been seen in Indiana or in other states in the past two years," Hunt said.
A class of insecticides called neonicotinoids, commonly used on soybean and corn seeds, has also been identified as a threat. In a 2012 study, Hunt and other researchers found high levels of concentrated neonicotinoids in dead bees around agricultural fields.
It is believed the neonicotinoids are absorbed by the talc used in planting and spread to surrounding plants and soil when the talc is released as exhaust from the planting machinery.
Another significant danger facing the bee population is a parasite known as a Varroa mite. The mites feed on bee larva and transmit viruses. If left unchecked, a mite infestation can destroy an entire colony.
The reddish-brown mites are tiny, but visible to the unaided eye. Beekeepers who notice too many mites in their hive should use a commercially available pesticide designed specifically to control Varroa mites, Hunt said.
"The earlier an infestation is identified, the better chance you have of saving the colony," he said.
Replacing a hive that has been lost or damaged by Varroa mites or other causes can be expensive and time-consuming, Hunt said.
"Normally, the bees are ready to pollinate in mid-May," he said. "If a beekeeper has to replace a colony, pollination could be delayed until mid-June."