The European Food Safety Authority (EFSA) has carried out reviews of the neonicotinoid pesticides thiamethoxam, imidacloprid and clothianidin in order to assess the possible risks posed by these systemic insecticides to bees.
These reviews helped underpin the decision by the European Commission to ban the three active ingredients from certain applications for a period of two years. In particular, the reviews identified shortcomings and gaps in the available data which prevented an holistic and exhaustive risk assessment from being carried out. One key uncertainty identified by EFSA in each case related to the role of guttation fluid exuded by commercial crop plants as a potential source of the chemicals to bees when they used it as a water source for themselves or for the colony as a whole.
The use of neonicotinoid insecticides as seed treatments and granules applied to soil is known to lead to these chemicals being present in the guttation fluid of various crop plants. Although the literature on this subject is sparse, the research carried out to date indicates that the neonicotinoids may be present at high concentrations. In order to investigate this phenomenon further, Greenpeace undertook a study of guttation fluid produced by maize plants grown in field conditions in Hungary, which according to the farmer had been treated with two different commercial seed treatment products. One field had been planted with seeds treated with Poncho®, with clothianidin as the active ingredient, while the other had been planted with seeds treated with Cruiser®, with thiamethoxam as the active ingredient. Samples of guttation fluid were sampled from each field over a number of days and analysed using UPLC-MS/MS techniques.
These findings, and their potential toxicological significance to bees both on an individual and whole colony level, suggests that, not only is the current restriction on the three neonicotinoid insecticides wholly justified, but that it should be maintained at least until the potential significance of guttation fluid as a water resource for bees is fully characterised, and until the other identified areas of uncertainty and missing information identified by EFSA are resolved. The scale and scope of the necessarily small-scale study conducted here needs to be expanded to include the full spectrum of crops grown using neonicotinoid seed dressings. In addition, the significance of guttation as a toxicological exposure route for bees needs to be investigated not only for a variety of crops but also under the full variety of growing conditions encountered for these crops across the European Community, in order to extend the currently highly limited information base available.
Dripping Poison - An analysis of neonicotinoid insecticides in the guttation fluid of growing maize plants [PDF]