Two new studies published simultaneously in the highly respected American journal Science, March 29, 2012, highlight the role of two neonicotinoid insecticides most commonly used to explain the decline of bees.
Assessment procedures and authorization of pesticides are to be reviewed urgently.
The effect of some pesticides on pollinators is accurate.
Two studies published March 29, 2012 in the journal Science shows how two insecticides of the neonicotinoid family – introduced in the early 1990s and now has become the most commonly used pesticides on crops worldwide – affect the development and the behavior of honey bees and wild species of bumblebee pollinators. All – and this is a great first – in field conditions and not in the laboratory, as was the case until now.
The first study, led by Penelope Whitehorn and Dave Goulson of the University of Stirling in the UK could explain, at least in part, the decline of some of the 20,000 species of wild pollinators.
« Some bumblebee species have declined dramatically in number. In North America, for example, some species that were widespread have more or less disappeared from the continent. In the UK, three species are now extinct », says Dave Goulson. The researchers exposed colonies of Bombus terrestris bumblebees to low levels of a neonicotinoid called Imidacloprid, used to make the famous Gaucho. The doses used were comparable to those, which are exposed to insects foraging crops treated with these pesticides.
The researchers placed the colonies in an enclosed area where the bees were feeding for six weeks under natural conditions. At the beginning and the end of the experiment, the researchers weighed each bumblebee nests that included animals, wax, honey, larvae and pollen to determine how much the colony had increased. It turns out that the colonies exposed to Imidacloprid took less weight compared to the control colonies, suggesting that they were fed less. At the end of the experiment, they were 8 to 12% smaller on average than the control colonies. They had also produced 85% less queens!
This is particularly important because the queen production is directly linked to the establishment of new nests after the winter dieback. Hence a significant reduction in their ability to regenerate, which could explain the observed decline found for a number of years.
« Bumblebees pollinate many crops and wildflowers. The use of neonicotinoids in crops is clearly a threat to their health and needs to be urgently reviewed », says Dave Goulson.
In the second article in Science, a French team found that the exposure to another neonicotinoid disrupted the ability of bees to find their hive, which caused the death of many of them. Mickaël Henry from the INRA of Avignon and his colleagues equipped 653 honeybees (Apis mellifera) with RFID microchips. This device allowed the researchers to track the bees in their back and forth between the hive and the environment. Then they gave half of them a small, non-lethal dose of Thiamethoxam, a substance of the neonicotinoid family with which the famous Cruiser is especially manufactured.
Compared to control bees that had not been exposed to the product, the treated bees were two to three times more likely to die outside the hive. The researchers argue that these deaths were likely to be produced because the pesticide interfered with the positioning system of the beehive.
In the second part of their study, the researchers used data from the tagging experiment with the bees to develop a mathematical model that simulates the dynamics of bee population. When mortality due to their lack of localization has been incorporated into these simulations, the model predicted that the bee populations exposed to pesticide were to decline to a level that did not allow their recovery.
The authorization procedures for pesticides are to be reviewed
Our study raises the important issue of authorization procedures for pesticides. So far, they mostly asked manufacturers to ensure that doses encountered in the field do not kill bees, but they have completely neglected the consequences of non-lethal doses, which however can cause behavioral problems, added Mickaël Henry, the author of the study. Following these studies, the Minister of Agriculture, Stéphane Le Foll, has banned the sale of the OSR Cuiser, which beekeepers demanded to be removed for years. This highly publicized event goes in the right direction of course. But it conceals the fact that several Cruiser insecticides still remain allowed in France, and many insecticides from the neonicotinoid family whose toxicity to bees has been proven by numerous studies of the INRA (the French National Institute for Agricultural Research) and the CNRS (the French National Centre for Scientific Research), and other labs in the United States, Canada, United Kingdom and Germany.
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