Bijensterfte, oorzaken en gevolgen

The Daily Yomiuri(Tokyo), May 19, 2009 Tuesday

The low buzzing of honeybees lingered on the sandbar in the middle of the Kisogawa river, on the border of Aichi and Gifu prefectures.

Workers wearing netting on their faces used bellows to blow smoke into the hives to calm the occupants, and quietly opened the beehives.

Workers at Api Co., a major honeybee supplier in Gifu Prefecture for bees that cross-fertilize fruit and vegetables, transfer between 2,000 and 8,000 honeybees from beehives into individual boxes destined for farms across the nation. The beehives are brought to Api by beekeepers.

The company acts like a bee broker. But for the past five years, demand for honeybees has exceeded supply. Last autumn, the company was forced for the first time to suspend shipments. And this spring, Western honeybees used to cross-fertilize plants with pollen were in short supply.

As the supply of honeybees declines, demand has only risen as greenhouse cultivation becomes more popular. And as farms and beekeepers begin to cooperate on ways to secure stable supplies of honeybees, researchers have begun looking into why the honeybees are disappearing.

At the end of April in Gunma Prefecture, a local beekeeping association decided to increase its number of honeybees in response to demands by the prefectural agricultural association that comprises vegetable farmers.

It decided to stop relying on brokers, and is aiming to secure a stable supply of bees through local efforts.

The beekeeping association's vice chairman, Kanji Fukuda, 56, said, "If we're able to make multiple queen bees stay in one colony during the spring-summer breeding season, we could double or triple the number of worker bees by autumn--when honeybees are needed for cross-fertilization."

Originally, beekeepers started lending honeybees to farmers who grow greenhouse strawberries during winter when the bees are not busy making honey for beekeepers.

Gradually, the period for growing strawberries grew, and farms started using the honeybees to fertilize melons, watermelons and eggplants. This is when brokers became involved in the business as farms sought a stable supply of honeybees.

According to Fukuda, honeybees are greatly stressed if they have to cross-fertilize in hot greenhouses containing agricultural products that supply only small amounts of pollen, which results in small amounts of honey.

A colony can survive longer when allowed to fly freely between flowers outdoors than when confined in greenhouses.

"Honeybees form a colony with a queen bee, worker bees and larvae, and the bees as a whole work together to form a unit that can be seen as a complete individual. If a colony lacks even one element, this balance is lost. They collect pollen so they can raise larvae. A colony was not meant to use worker bees just to cross-fertilize plants with pollen," Fukuda said.

A colony consists of tens of thousands of female worker bees, male bees and one queen. Female bees outnumber male bees 9:1.

According to a study by the Agriculture, Forestry and Fisheries Ministry, the number of honeybee colonies kept by beekeepers has decreased by 4 percent to about 173,000 as of January 2008 compared with a year ago.

Among them, the number of honeybee colonies for cross-fertilization has decreased by 14 percent from the previous year to about 33,000.

According to a questionnaire last year sent by a research team led by Kiyoshi Kimura of the National Institute of Livestock and Grassland Science in Tsukuba, Ibaraki Prefecture, 23 percent of about 800 beekeepers said they had honeybee populations disappear for unknown reasons.

One suspected cause is the use of an agricultural chemical for killing stinkbugs.

"Though the short-lived worker bees look normal, it's likely that when they were larvae they were affected by agricultural chemicals via pollen," Kimura, who plans to test this theory, said.

Another possibility is that a pesticide has failed to eliminate parasitic ticks. If such ticks are exposed to chemicals, such as pesticides for gardening, in low concentrations, the ticks' genes adapt to dissolve the poison inside their bodies.

"Such multiple causes as parasitic ticks, stress from greenhouse cultivation and infection by a virus might have led to the massive deaths [of worker bees]," Tatsuhiko Kadowaki, 45, an associate professor of Nagoya University, said.

Kadowaki started collecting samples of honeybees across the nation from this fiscal year in cooperation with the Japan Beekeeping Association, and started testing them for seven kinds of virus peculiar to honeybees.

From all 27 samples Kadowaki checked, he detected two kinds of viruses that transformed the shape of wings or caused a disease only affecting queen bee larvae.

Meanwhile, he detected a virus in 14 samples that caused fluid accumulation under the skin of larva. This same virus caused massive deaths in Japanese honeybees in the 1980s.

The samples showed that not all honeybees are affected by the same causes.

"It's also possible that imported queen bees brought new viruses to Japan. I'd like to pinpoint the relation between the massive deaths and any pathogen," Kadowaki said.

www.yomiuri.co.jp/dy/national/20090519TDY04303.htm