Concern about the unexplained decline in bee populations, affecting not only domesticated bees but their wild cousins, bumblebees, and solitary bees aswell, led stake holders to join forces. Working as a part of an interdisciplinary partnership to assess bee die off (see boxed text), scientists from INRA and the CNRS, and agriculture and apiculture engineers from ACTA, ITSAP-Institut de l’abeille and ADAPI studied the link between in gestion of a neonicotinoid insecticide and forager mortality. Their works hows that exposure to a low and significantly less than lethal – dose of the insecticide led to bee losses two to three times higher than normal.
Researchers used an innovative method to carry out the study. They attached RFID microchips to the thoraces of more than 650 bees, and were thus able to monitor each bee’sentry or exit from the hive through a series of electronic sensors. Half of the bees were fed sugar water that contained a very low dose of insecticide,similar to what might be encountered over the normal course of nectar foraging in a treated crop.
In the control group, the other half of the bees were fed sugar water that did not contain insecticide. All of the bees were then released one kilometre from their hive, the usual foraging distance for domesticated bees. The researchers compared the proportion of bees from each group that returned to the hive inorder to determine the loss rate attributable to ingestion of the insecticide.The team found a significant rate of failure to return to the hive for the exposed group, owing to disorientation caused by low-level intoxication. Insecticide-related bee loss, when combined with natural mortality rates, results in a daily mortality rate of 25% to 50% in intoxicated foraging bees three times higher than the normal daily forager mortality rate of approximately 15%.
A computer model simulating the makeup of a bee colony was used to evaluate the impact ofhigher mortality rates during the flowering period. When the study’s findings were input into the model, the results showed that if most foragers were contaminated each day, the colony’s population could be halved during the flowering period, or even drop by as much as 75% in worst-case scenarios. Such a population drop would come at a critical time when the colony’s population level should be at its highest, which is a precondition for stocking food reserves and honey production.
Disorientation, therefore, has the potential to undermine the colony’s natural development, and may make it vulnerable to other stress factors such as pathogens like Varroa, nosema, or viruses, or the availability of natural flower resources. The studys hows that the long-term survival of the colony may be affected by forager bees exposed to neonicotinoid insecticide, even when exposed to considerably less than fatal amounts.
In the nearterm, partners from the PrADE (Protecting Bees in the Environment) Joint Technological Unit, together with ARVALIS-Institut du vegetal and CETIOM, two technical agricultural institutes specialising in field crops, notably maize and rapeseed, will carry out full-scale experiments under real crop conditions, including the period when insecticide is applied, using the same RFID technology to monitor bees individually.