(NaturalNews) The hypothesis that neonicotinoid insecticides are the primary factor responsible for the ongoing collapse of honeybee colonies has been strengthened in a study conducted by researchers from the Harvard School of Public Health and the Worcester County Beekeepers Association, and published in the Bulletin of Insectology on May 9.
The study, which showed that two varieties of neonicotinoids induce colony collapse disorder (CCD) among honeybee colonies during the winter, replicated earlier findings from the same researchers.
"We demonstrated again in this study that neonicotinoids are highly likely to be responsible for triggering CCD in honey bee hives that were healthy prior to the arrival of winter," lead author Chensheng (Alex) Lu said.
Honeybee collapse may cause food crisis
Since 2006, honeybees in numerous countries have been devastated by CCD, in which bees abandon their hives over the winter and die. The ongoing crisis has raised grave concern for its potential effects on the global food supply, one-third of which is dependent upon honeybees. Honeybees are used to pollinate 130 different crops, with an annual value of $15 billion.
Numerous explanations have been investigated for CCD, including pathogens and pesticides. A 2012 study by the same research team linked the neonicotinoid pesticide imidacloprid specifically to the phenomenon.
In the new study, researchers studied 18 separate bee colonies at three locations in central Massachusetts between October 2012 and April 2013. One-third of the colonies at each location were treated with imidacloprid, one-third with the neonicotinoid clothianidin and one-third left untreated.
As expected for honeybees in New England, all 18 colonies experienced a decline in size during the beginning of the winter. By January, populations in the untreated colonies had begun to increase again, as expected for a healthy hive. In the neonicotinoid-treated hives, however, populations continued decreasing. By April, 50 percent of the neonicotinoid-treated colonies had been permanently abandoned in a fashion consistent with CCD.
In contrast, only one of the untreated colonies was lost, with bees found dead inside the hive due to a common parasitic infection (Nosema ceranae) -- rather than with the empty hives characteristic of CCD. Other than this one hive, pathogen infestation rates were similar between the CCD and the non-CCD colonies, suggesting that parasites are not primarily responsible for CCD. Instead, the neonicotinoids appear to be causing some other form of harm to the bees.
Parasitic infestation may still be a factor in the overall honeybee decline, however. A 2013 study published in the journal PLOS ONE found that common agricultural fungicides reduce bees' resistance to Nosema ceranae infection.
The prior study found an even higher impact of neonicotinoids, with 94 percent of treated hives experiencing CCD. The researchers believe that this discrepancy might be explained by the fact that the original study was conducted during an especially cold winter. Perhaps, they suggested, neonicotinoids somehow make honeybees more vulnerable to the cold.
"Although we have demonstrated the validity of the association between neonicotinoids and CCD in this study, future research could help elucidate the biological mechanism that is responsible for linking sub-lethal neonicotinoid exposures to CCD," Lu said. "Hopefully we can reverse the continuing trend of honey bee loss."
Wild pollinators also threatened
In addition to honeybee collapse, global food populations are also threatened by ongoing declines in populations of native pollinators, largely due to the loss of wild and semi-wild habitats. According to a study published in the journal Science in 2013, roughly three-quarters of all human food crops depend upon animal pollination. In addition, wild pollinators are actually more effective pollinators, in most cases, than domestic honeybees, producing healthier crops and larger yields.