French study claims "missing link" in pesticide effects on bees
The issue of neonicotinoids' impacts on bee populations is one of the most controversial debates for the global produce industry right now, with three 'neonic' pesticides banned in the European Union while the U.S. Environmental Protection Agency (EPA) has required bee safety studies to investigate the chemicals' effects. How the regulations turn out will affect growers' fates as neonics are present in around 30% of insecticide use worldwide.
This is why a recent French study published in Royal Society journal Proceedings B is so relevant.
The authors of the study 'Reconciling laboratory and field assessments of neonicotinoid toxicity to honeybees' sought to address discrepancies between results in the lab and the field.
"Although laboratory trials report deleterious effects in honeybees at trace levels, field surveys reveal no decrease in the performance of honeybee colonies in the vicinity of treated fields," the authors said.
"Here we provide the missing link, showing that individual honeybees near thiamethoxam-treated fields do indeed disappear at a faster rate, but the impact of this is buffered by the colonies' demographic regulation response."
Through the use of tags and RFID readers on hives, the researchers monitored 6,847 individual bees from 17 colonies near rapeseed oil fields.
"This study follows the recommendations of ANSES, the French food safety agency, to reassess the possible side effects of thiamethoxam under real agricultural usage conditions," the authors said, adding it was given permission to undertake the study by French authorities.
"Honeybees disappeared at a faster rate with increasing field exposure and this excess mortality increased over time.
"In spite of the excess mortality measured at the individual scale, highly exposed colonies did not show altered performance per se in terms of population growth and honey and brood production."
The scientists did point out however that there was a change in the way reproductive effort was allocated between female (worker) brood and drone (male disperser) brood.
However, there was a change in the way reproductive effort was allocated between female (worker) brood and drone (male disperser) brood.
"During flowering, the most exposed colonies tended to invest more in worker brood production at the expense of drone brood production.
"Drone brood development was delayed in exposed colonies; after flowering, drone brood production followed the field exposure gradient, being significantly higher in the more exposed hives.
"Rather than a decline in colony performance strictly speaking, these patterns should be viewed as a by-product of colonies' demographic compensation and regulation of reproductive investment."
In essence, this means male bees are born during foraging periods, and this delayed drone production might "somehow disrupt this biological synchrony, and should therefore be addressed in terms of mating success or fitness value of reared drones".
The researchers encouraged this last issue to be explored along with colony performance metrics using large colony monitoring datasets.