Are neonicotinoids at the root of the honey bee crisis?

A growing body of research, outlined in a new review in Bee World, attests to a link between neonicotinoids – the leading agricultural insecticides worldwide – and the global collapse of honey bee colonies, say authors Francisco Sánchez-Bayo and Nicolas Desneux.

The authors, from the University of Sydney, Australia, and INRA, France, state that it is well known that the decline of bee colonies is correlated with the increasing use of insecticides in agriculture in the past six decades. They point out that in the United States, for example, around 40% of bee colonies are lost annually, a figure well above the natural rate of 10-15%. The authors suggest that in countries that have switched to neonicotinoid insecticides, there has been a marked increase in parasite infections, particularly Varroa destructor and Nosema ceranae, and a higher prevalence of viral diseases such as deformed wing virus.

Older insecticides are typically fat-soluble and kill insects by contact, being applied by spraying, affecting many organisms apart from the target pest. In contrast, neonicotinoids are water-soluble chemicals that are taken up by plants and translocated to all their tissues, controlling sap sucking insects directly. Their residues may, however, appear in the pollen and nectar of crops, and other surrounding plants, to be either consumed directly by bees or stored in their hives as bee-bread and honey.

These systemic insecticides can also suppress bees’ immune systems; recent developments have demonstrated that sub-lethal levels of the insecticides imidacloprid and clothianidin leave bees defenceless against virus proliferation.

In conclusion, according to author Francisco Sánchez-Bayo, "systemic insecticides are the ultimate cause of this complex crisis of honey bee health”. Other pollinators, including butterflies and hoverflies, and predatory insects, such as wasps and ladybirds, are also exposed to neonicotinoids due to agriculture, as well as coming into contact with contaminated surface waters as a result of their use in nurseries, domestic gardens and urban parks. “The impact that these systemic insecticides are having on the ecosystems built upon these myriad insects could therefore seriously compromise the sustainability of agricultural production”.