A new study from Harvard implicates two neonicotinoid pesticides, imidacloprid and clothianidin, in the ongoing plague of honeybee Colony Collapse Disorder. Imidacloprid is the most widely used pesticide in the world, and both are approved by the EPA. 
 
 A team of Harvard biologists has come closer to cracking the mystery of honeybee Colony Collapse Disorder (CCD), eight years after its appearance. 
 
 CCD persists in transforming bee colonies around the world into ghost towns: by the end of each winter, some colonies wind up littered with dead bees and emptied of many more, with no signs of renewal. 
 
 "One of the defining symptomatic observations of CCD colonies is the emptiness of hives in which the amount of dead bees found inside the hives do not account for the total numbers of bees present prior to winter when they were alive," states the report, published May 9 in the Bulletin of Insectology. 
 
 The exact mechanism behind these collapses remains dauntingly unclear, but they have been linked with pathogen infestation, malnutrition, and pesticide exposure. This week's report strongly indicates that two neonicotinoid insecticides that are widely used on crops can decimate honeybee colonies' winter survival rates, whether or not mites or parasites are present. 
 
 The two chemicals, imidacloprid and clothianidin, both block insects' central nervous systems, killing them by paralysis. Imidacloprid is the world's most widely-used insecticide, and has been registered for use in the US since the 1994; clothianidin was registered in 2003 by the US Environmental Protection Agency, which found that it had passed honeybee-specific toxicity tests. 
 
 These scientists studied the health of 18 bee colonies in central Massachusetts over a six-month period spanning the winter of 2012-2013. Six of the colonies were fed sugar spiked with sub-lethal doses of imidacloprid, six had theirs laced with clothianidin, and six less-unfortunate control colonies ate clean sugar, starting in October. 
 
 All of the colonies went about their apian routines in good form throughout the fall. But by late January, six of the 12 poisoned colonies experienced collapses with CCD-like symptoms, like en-masse disappearance and the presence of un-hatched young. Of the six control hives, only one failed to survive the winter, seemingly due to an infestation by Nosema Ceranae parasites. 
 
 "The honey bee clusters in the six surviving neonicotinoid treated colonies were very small, and were either without queen bees or had no brood," reports the study, suggesting the poisons harm the animals' abilities to raise and train new young. In contrast, the five surviving control hives replenished their populations quickly, as the winter gave way to spring. 
 
 According to the report, these results "reinforce the conclusion that sublethal exposure to neonicotinoids is likely the main culprit for the occurrence of CCD." 
 
 The finding raises a large question for further study: Why do honeybees, who don't normally abandon their hives during winter, do so when poisoned by neonicotinoids? 
 
 The finding may point to "the impairment of honey bee neurological functions, specifically memory, cognition, or behavior, as the results from the chronic sublethal neonicotinoid exposure," suggest the authors. "Although the failure to initiate brood rearing and the vanishing of the worker caste in the neonicotinoid-treated colonies might be governed by completely different mechanisms, they suggest the possible involvement of cascading events prior to the occurrence of CCD." 
 
 The study comes amid a busy spring season for honey bee research. Last month a team of Kenyan biologists found that African honey bees seem be impervious to the pests, Varroa and Nosema, which plague honey bee populations in Europe, Asia, and the United States. 
 
 And earlier this week Brazilian scientists identified two substances in honeybees' brains, that appear to vary as the insects move through space and time, guiding their age-related division of labor. ||||| Two widely used neonicotinoids — a class of insecticide — appear to significantly harm honeybee colonies over the winter, particularly colder winters, according to a new study from Harvard School of Public Health (HSPH). The study replicated a 2012 finding from the same research group that found a link between low doses of imidacloprid and Colony Collapse Disorder (CCD), in which bees abandon their hives over the winter and eventually die. The new study also found that low doses of a second neonicotinoid, clothianidin, had the same negative effect. 
 
 Further, although other studies have suggested that CCD-related mortality in honeybee colonies may come from bees’ reduced resistance to mites or parasites as a result of exposure to pesticides, the new study found that bees in the hives exhibiting CCD had almost identical levels of pathogen infestation as a group of control hives, most of which survived the winter. This finding suggests that the neonicotinoids are causing some other kind of biological mechanism in bees that in turn leads to CCD. 
 
 The study appears online May 9 in the Bulletin of Insectology. 
 
 “We demonstrated again in this study that neonicotinoids are highly likely to be responsible for triggering CCD in honeybee hives that were healthy prior to the arrival of winter,” said lead author Chensheng (Alex) Lu, associate professor of environmental exposure biology at HSPH. 
 
 Since 2006, CCD has caused significant losses of honeybees. Pinpointing the cause is crucial to mitigating this problem since bees are prime pollinators of roughly one-third of all crops worldwide. Experts have considered a number of possible causes, including pathogen infestation, beekeeping practices, and pesticide exposure. Recent findings, including a 2012 study by Lu and colleagues, suggest that CCD is related specifically to neonicotinoids, which may impair bees’ neurological functions. Imidacloprid and clothianidin both belong to this group. 
 
 Lu and his co-authors from the Worcester County Beekeepers Association studied the health of 18 bee colonies in three locations in central Massachusetts from October 2012 through April 2013. At each location, the researchers separated six colonies into three groups — one treated with imidacloprid, one with clothianidin, and one untreated. 
 
 There was a steady decline in the size of all the bee colonies through the beginning of winter — typical among hives during the colder months in New England. Beginning in January 2013, bee populations in the control colonies began to increase as expected, but populations in the neonicotinoid-treated hives continued to decline. By April 2013, six out of 12 of the neonicotinoid-treated colonies were lost, with abandoned hives that are typical of CCD. Only one of the control colonies was lost — thousands of dead bees were found inside the hive — with what appeared to be symptoms of a common intestinal parasite called Nosema ceranae. 
 
 While the 12 pesticide-treated hives in the current study experienced a 50 percent CCD mortality rate, the authors noted that in their 2012 study, bees in pesticide-treated hives had a much higher CCD mortality rate — 94 percent. That earlier bee die-off occurred during the particularly cold and prolonged winter of 2010-11 in central Massachusetts, leading the authors to speculate that colder temperatures, in combination with neonicotinoids, may play a role in the severity of CCD. 
 
 “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,” said Lu. “Hopefully we can reverse the continuing trend of honeybee loss.” 
 
 Funding for the study came from the Wells Fargo Foundation and the Breck Fund at the Harvard University Center for the Environment.
– A new Harvard study adds more evidence to the theory that insecticides are the main culprit in the disappearance of honeybees, reports the Christian Science Monitor. Researchers found that bees in Massachusetts exposed to a common class of insecticides known as neonicotinoids suffered significant drops in numbers over the winter compared with bees who had no such exposure. In the study, only six of 12 colonies exposed to the chemicals imidacloprid and clothianidin survived the winter. Of six non-exposed colonies, all but one made it. Imidacloprid is the world's No. 1 pesticide and has been registered in the US since 1994, says the Monitor. "We demonstrated that neonicotinoids are highly likely to be responsible for triggering 'colony collapse disorder' in honeybee hives that were healthy prior to the arrival of winter," says one of the Harvard researchers, as quoted in the Guardian. The scientists speculate that the chemicals impair the bees' neurological functions, causing them to first abandon their colonies and then die. Based on comparisons with a previous study, the researchers also think that particularly harsh winters can worsen the effects of CCD, reports the Harvard Gazette.