A Four-Year Field Program Investigating Long-Term Effects of Repeated Exposure of Honey Bee Colonies to Flowering Crops Treated with Thiamethoxam

Abstract

Neonicotinoid residues in nectar and pollen from crop plants have been implicated as one of the potential factors causing the declines of honey bee populations. Median residues of thiamethoxam in pollen collected from honey bees after foraging on flowering seed treated maize were found to be between 1 and 7 µg/kg, median residues of the metabolite CGA322704 (clothianidin) in the pollen were between 1 and 4 µg/kg. In oilseed rape, median residues of thiamethoxam found in pollen collected from bees were between <1 and 3.5 µg/kg and in nectar from foraging bees were between 0.65 and 2.4 µg/kg. Median residues of CGA322704 in pollen and nectar in the oilseed rape trials were all below the limit of quantification (1 µg/kg). Residues in the hive were even lower in both the maize and oilseed rape trials, being at or below the level of detection of 1 µg/kg for bee bread in the hive and at or below the level of detection of 0.5 µg/kg for hive nectar, honey and royal jelly samples. The long-term risk to honey bee colonies in the field was also investigated, including the sensitive overwintering stage, from four years consecutive single treatment crop exposures to flowering maize and oilseed rape grown from thiamethoxam treated seeds at rates recommended for insect control. Throughout the study, mortality, foraging behavior, colony strength, colony weight, brood development and food storage levels were similar between treatment and control colonies. Detailed examination of brood development throughout the year demonstrated that colonies exposed to the treated crop were able to successfully overwinter and had a similar health status to the control colonies in the following spring. We conclude that these data demonstrate there is a low risk to honey bees from systemic residues in nectar and pollen following the use of thiamethoxam as a seed treatment on oilseed rape and maize.

Pesticide risk assessment in free-ranging bees is weather and landscape dependent

“…They may thus rather be viewed as environments with greater challenge imposed upon honeybee navigation during poor weather conditions, where any treatment effect will be harder to detect. Notwithstanding, with the help of experts' assessment of the field exposure levels 29,30 and how they compare with ED 20 values, this approach allows determining the proportion of the landscape at risk of detrimental HF in case of exposure.…”

Combined effect of pollen quality and thiamethoxam on hypopharyngeal gland development and protein content in Apis mellifera

“…Thiamethoxam is a neonicotinoid insecticide, characterised by a high acute toxicity to honeybees (oral LD 50 5 ng/bee, EFSA 2013) and capable of causing detrimental effects also at sublethal doses. This scenario is likely to occur as honeybees can be exposed to residues of thiamethoxam in fresh pollen (Dively and Kamel 2012;Pilling et al 2013) and bee bread (Mullin et al 2010). The effects provoked by the ingestion of sublethal concentrations of this insecticide may entail the impairment of orientation capacities (Henry et al;, olfactory learning (Aliouane et al 2009) and queen quality (Williams et al 2015).…”

Weight of evidence evaluation of a network of adverse outcome pathways linking activation of the nicotinic acetylcholine receptor in honey bees to colony death

“…Although numerous studies report effects of neonicotinoids on foraging behavior in bees, some contradictory evidence following exposure to the neonicotinoids also has been reported (Dively et al, 2015;Franklin et al, 2004;Pilling et al, 2013). Some of these studies examined the effects on foraging after exposure to seed-treated crops; however, Dively et al (2015) fed 10 replicate colonies 0, 2, 20, or 100 μg/kg imidacloprid over a 12-week period, reporting no adverse effects on foraging activity as measured by the number of foragers returning to the hive or the number of animals loaded with pollen pellets.…”