Behaviour of Imidacloprid in Fields. Toxicity for Honey Bees

Abstract

Following evidence for the intoxication of bees, the systemic insecticide imidacloprid was suspected from the mid nineties of having harmful effects. Recently, some studies have demonstrated that imidacloprid is toxic for the bees at sub-lethal doses. These doses are evaluated in the range between 1 and 20 μg kg -1 , or less. It appeared thus necessary to study the fate of imidacloprid in the environment at such low levels. Thus, we developed methods for the determination of low amounts, in the μg kg -1 range, of the insecticide imidacloprid in soils, plants and pollens using high pressure liquid chromatography -tandem mass spectrometry (LC/APCI/MS/MS). The extraction and separation methods were performed according to quality assurance criteria, good laboratory practices and the European Community's criteria applicable to banned substances (directive 96/23 EC). The linear concentration range of application was 1-50 μg kg -1 of imidacloprid, with a relative standard deviation of 2.9% at 1 μg kg -1 . The limit of detection and quantification are respectively LOD = 0.1 μg kg -1 and LOQ = 1 μg kg -1 and are suited to the sub-lethal dose range. This technique allows the unambiguous identification and quantification of imidacloprid. The results show the remanence of the insecticide in soils, its ascent into plants during flowering and its bioavailability in pollens.

REVIEW: An overview of the environmental risks posed by neonicotinoid insecticides

“…Bonmatin et al . () randomly sampled 74 farmland soils in France and screened them for imidacloprid. Seven soils from organic farms contained no imidacloprid.…”

Risk assessment to honey bees: a scheme developed in France for non‐sprayed systemic compounds

“…It may also be considered in a longer timescale that is defined by the fate of the product applied in the field. Slowly dissipating substances may, if they remain in significant amounts in the soil after harvest, be mobilised by the following crop, the attractiveness of which becomes a key question for the risk assessment 11, 12. The occurrence of translocations of soil residues in succeeding crops is commonly assessed in the European review process1 and mainly relies on field data.…”

“…Other studies demonstrate the translocation of residues in nectar after soil treatment with granules 15. However, very few studies have focused on the analysis of nectar or pollen for pesticide residues after soil or seed treatments, although available results indicate the presence of quantifiable amounts of residues11, 12, 16–18 that may in some cases result in the need to proceed to a risk assessment 18…”

“…Studies measuring residue concentrations in nectar or pollen indicate that the amounts of residues reaching these matrices may correspond to variable fractions of the dose applied, depending on the plant species and environmental conditions 16, 21. Studies comparing residue levels among plant parts, and particularly between green or edible parts and nectar or pollen, are sparse 11, 12, 16. Translocation of pesticides is specified to be measurably less effective to fruiting structures than to other plant parts,22 but a generalisation on a far lower contamination of these structures compared with the green parts would be premature.…”

“…In the abovementioned studies,13–15 residues in nectar were quantified at mg kg −1 plant material levels that were toxic to both honey bee larvae and adults. The methods developed to analyse residues in whole plants or in green parts may not always be appropriate for analysing residues in nectar (Venant A, private communication) or pollen 11, 12. The collection of pollen or nectar in sufficient amounts for validation purposes and further analyses is a key issue.…”