Neonicotinoid Residues in Wildflowers, a Potential Route of Chronic Exposure for Bees

Abstract

In recent years, an intense debate about the environmental risks posed by neonicotinoids, a group of widely used, neurotoxic insecticides, has been joined. When these systemic compounds are applied to seeds, low concentrations are subsequently found in the nectar and pollen of the crop, which are then collected and consumed by bees. Here we demonstrate that the current focus on exposure to pesticides via the crop overlooks an important factor: throughout spring and summer, mixtures of neonicotinoids are also found in the pollen and nectar of wildflowers growing in arable field margins, at concentrations that are sometimes even higher than those found in the crop. Indeed, the large majority (97%) of neonicotinoids brought back in pollen to honey bee hives in arable landscapes was from wildflowers, not crops. Both previous and ongoing field studies have been based on the premise that exposure to neonicotinoids would occur only during the blooming period of flowering crops and that it may be diluted by bees also foraging on untreated wildflowers. Here, we show that exposure is likely to be higher and more prolonged than currently recognized because of widespread contamination of wild plants growing near treated crops.

Reconciling laboratory and field assessments of neonicotinoid toxicity to honeybees

“…Imidacloprid was undetected in the nectar of 30 sampled fields (36.6%), and varied from 0.1 to 1.6 ppb (median ¼ 0.4 ppb) in the remaining 52 fields (63.4%). Those results concur with the substantial re-uptake of neonicotinoid residues recently reported in pollen and nectar samples from wild flowers in field margins [48], sometimes at even higher concentrations than in the flowering crop nectar itself. Various hypotheses may be proposed for those observations, including the persistence and accumulation of neonicotinoid residues in the soil throughout one or more annual crop succession cycles, their lateral movement and leaching in adjacent slopes, or even possible contaminations via the seed-coating machinery [48].…”

“…Those results concur with the substantial re-uptake of neonicotinoid residues recently reported in pollen and nectar samples from wild flowers in field margins [48], sometimes at even higher concentrations than in the flowering crop nectar itself. Various hypotheses may be proposed for those observations, including the persistence and accumulation of neonicotinoid residues in the soil throughout one or more annual crop succession cycles, their lateral movement and leaching in adjacent slopes, or even possible contaminations via the seed-coating machinery [48]. The precise pathway by which imidacloprid used on wheat or barley can transfer to oilseed rape nectar later on therefore requires urgent clarification because it is liable to compromise any effort scientists and risk assessors make to reconcile the findings of laboratory and field exposure surveys.…”

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

“…A field study conducted in southern England showed that neonicotinoids used as seed dressing for autumn-sown crops (oil seed rape (OSR) and winter wheat) contaminated adjacent soil and wildflowers (Botias et al 2015). The pollen and nectar of these flowers were contaminated by thiamethoxam, clothianidin, imidacloprid, and thiacloprid (up to a frequency of 58.8%) in the following growing season with frequencies and concentrations declining between spring and summer.…”

Pollinators and Global Food Security: the Need for Holistic Global Stewardship

“…These neurotoxic agrochemicals act systemically: during growth the active substance is taken up by the roots and makes the whole plant toxic to insects for a long period. Unintendedly, neonicotinoids also end up in nectar and pollen, which are the food sources for bees (Botías et al 2015; Van der Sluijs 2013a).…”

“…Through systemic uptake it also contaminates wild flowers (Botías et al 2015). In the Netherlands levels of imidacloprid (the most widely used neonicotinoid, introduced in 1994 as an insecticide to coat sunflower seeds with before planting) far in excess of what is considered safe for aquatic ecosystems have been measured continually in the surface water since 2004 (Van Dijk et al 2013), 1000 to 25,000 times the Maximum Permissible Concentration in the Netherlands of 13 ng l −1 .…”