Ironically, the relatively new pesticides have been welcomed as an environmental plus because they are, by almost all accounts, less harmful to other wildlife than previous generations of pesticides.
Although the authors of the studies published Thursday in the journal Science do not conclude that the pesticides — called neonicotinoids — are the sole cause of the American and international decline in bees or the more immediate and worrisome phenomenon known as colony collapse disorder, they say that the omnipresent chemicals have a clearly harmful effect on beehives.
“People have asked me to sign petitions to ban or limit the use of the neonicotinoids for some time, but I never did because I really didn’t know if they were having a major impact on the bees,” said David Goulson of the University of Stirling in Britain, co-author of one of the studies.
“After seeing what we and the others found, I’m much more inclined to sign.”
Unlike older pesticides, the neonicotinoid pesticides are most often introduced directly into the seeds of crops planted by farmers and thus permeate the entire plant as it grows — including the pollen and nectar the bees feed on.
Spraying of the older pesticides could be halted when plants were flowering so bees and other pollinators would not be harmed. With the neonicotinoids, which kill pest insects by attacking their central nervous systems and are derived from the same nicotine found in tobacco, that kind of timing is not possible.
Failure to thrive
The initial changes in bee behavior found by the researchers may have been small, but the longer-term impact was large: Researchers found a sharp drop in the number of queen bumblebees produced, a decrease in the size and weight of beehives, and a demonstrated increase in the number of bees unable to find their way home. When the hives as a whole don’t thrive, then the individuals become more susceptible to disease and other threats.
The subject became a major focus of agricultural and environmental attention in 2006 when beekeepers reported massive losses in their beehives, an escalation of a decline seen for years.
The new research — one study of honeybees and the other of bumblebees — points to flaws in the way pesticides are evaluated by regulators, said the author of the study of a kind of honeybee widely used as a pollinator in agriculture.
“So far, they mostly require manufacturers to ensure that doses encountered on the field do not kill bees, but they basically ignore the consequences of doses that do not kill them but may cause behavioral difficulties,” said Mickael Henry of the French National Institute for Agricultural Research (INRA) in Avignon, France.