What happens when bees get an overdose of pesticide? They die.                Photographer: Phil Hawkins/Bloomberg
What happens when bees get an overdose of pesticide? They die.                Photographer: Phil Hawkins/Bloomberg

For activists eager to blame pesticides for the declining health of bees, researcher Chensheng Lu has offered what looks like valuable ammunition and the credibility provided by his affiliation with Harvard's School of Public Health. Lu and his associates have just published a second study implicating a class of insecticides called neonicotinoids, which the European Union has banned for two years. What Lu's research actually does, however, is distract attention from the need to limit more of the real causes of bee deaths.

Neonicotinoids are an obvious suspect in the unusually high over-winter losses U.S. beekeepers have been reporting since 2006, a concern given the important role farmed bees play in agriculture, adding an estimated $15 billion annually to the value of crops. Neonicotinoids have grown in use over that same period and certainly can kill bees if used improperly. The question is whether they harm bee colonies during normal use.

To test that hypothesis, Lu has twice conducted studies in which he and his co-researchers have fed bees neonicotinoid-laced syrup. Yet in both trials, they used dosages far in excess of anything bees would encounter in agricultural fields.

In a study published in 2012, Lu's team began with concentrations that approximated those typically found in the nectar of neonicotinoid-treated crops: 0.1, 1, 5 and 10 micrograms of pesticide per kilogram of syrup. After a month, however, they inexplicably jacked up the doses to unrealistic levels: 20, 40, 200 and 400 micrograms. Not surprisingly, 15 of 16 insecticide-tainted colonies eventually died.

In the new study, researchers didn't waste time with a low initial dose. They began right away with syrup containing 136 micrograms of insect-killer per liter. Eventually, six of the 12 colonies fed the spiked syrup failed. Calling the researchers' credibility into further question, the second study, like the first, ascribes colony failure to colony collapse disorder, a malady with characteristics not evident in either trial.

In any case, it should be noted that whatever results the researchers created in the lab, in trials in which bees have been placed in farm fields treated with neonicotinoids, the colonies have done fine.

Lu's new study nonetheless is receiving significant -- and largely uncritical -- media attention and strengthening the call by some environmentalists to prohibit neonicotinoid use in the U.S. Such a ban would be a mistake. It would compel U.S. farmers to use older pesticides that haven't been subjected to bee studies and may be more hazardous to cultivated bees, not to mention wildlife and humans.

What's more, the focus on neonics draws attention away from more plausible causes of bee deaths. First is the Varroa mite, which spreads lethal infections and has developed resistance to miticides. More research is needed on strategies to defeat this parasite.

Second is the decline in bee food sources. High corn and soybean prices have accelerated the conversion of open land to cropland, leaving bees little to eat outside of the few weeks when a crop blossoms. Maybe if the government limited the subsidies that encourage fence-to-fence single-crop planting, more marginal land would be left fallow and could feed bees.

It would also help if states let flowering weeds grow alongside highways and planted native flowers in parks and public spaces. Certainly, more studies showing that bees tend to die when fed concentrations of insect-killer they would otherwise never encounter don't help.

To contact the writer of this article: Lisa Beyer at lbeyer3@bloomberg.net.

To contact the editor responsible for this article: James Greiff at jgreiff@bloomberg.net.