How a new class of pesticides transformed the agrochemical landscape for bees

bee foraging photo
CC BY-ND 2.0 Lavender's Legacy - by Ryan

Even as Europe enacts a 2-year precautionary ban on neonicotinoid pesticide use on crops attractive to bees, the pesticide makers are crying foul—claiming that there is insufficient evidence for such supposedly drastic measures.

With each new study, however, such claims are being increasingly tested.

Whether it's evidence that exposure to seed insecticide dust leads directly to bee deaths, or research showing that sublethal doses of neonicotinoids can disrupt breeding, navigation and other crucial functions in both honeybees and bumblebees alike, there are an increasing number of data points suggesting that we have something to worry about.

Now a review of the research into honeybees and neonicotinoids published in the Elsevier journal Current Opinion in Environmental Sustainability aims to bring those data points together.

The picture that emerges is not a pretty one:

At field realistic doses, neonicotinoids cause a wide range of adverse sublethal effects in honeybee and bumblebee colonies, affecting colony performance through impairment of foraging success, brood and larval development, memory and learning, damage to the central nervous system, susceptibility to diseases, hive hygiene etc. Neonicotinoids exhibit a toxicity that can be amplified by various other agrochemicals and they synergistically reinforce infectious agents such as Nosema ceranae which together can produce colony collapse.

In addition to the focus on dosage and toxicity, the team of researchers—lead by Jeroen P van der Sluijs from the Utrecht University—points to a number of other alarming factors including the persistence of neonicotinoids in the soil and water, which consequently leads to uptake by other non-target plants which in turn increases availability to foraging insects like bees:

The systemic properties of neonicotinoids imply translocation to pollen, nectar, and guttation droplets. The persistency and potential contamination of wild plants and trees surrounding the treated crops and the possibility for travelling far outside the fields via surface and ground water and the potential to contaminate wild plants and crops that take up polluted water, means that pollinating insects are likely to be exposed for much of the year to multiple sources of multiple neonicotinoids in their foraging area, but often at very low doses.

The team also highlights concerns around the validity of the field tests used to approve these new pesticides, suggesting that it may be almost impossible to set up "control" colonies out in the field that are not exposed to neonicotinoids. They also argue that because bees act as a "superorganism" reliant on the health of the colony, a scientific focus on individual bee mortality may mask systemic effects which undermine the survival of the colony as a whole. (For example, forager bees' increased susceptibility to insecticide exposure may put the survival of the colony at disproportionate risk.)

In a sobering reminder that there is still much work to do, van der Sluijs et al. remind us that despite the recent temporary ban by European legislators, the global production of neonicotinoids is still increasing. I guess we really do need action on the local, regional and international scale to help protect our bees.

How a new class of pesticides transformed the agrochemical landscape for bees
In just twenty years, neonicotinoid pesticides became the most widely used insecticides in the world. Evidence is mounting that this rise has been a disaster for bees.

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