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.
Highlights
Honey bees provide a vitally important role, both ecologically by pollinating wild plants, and economically by providing a pollination service to a variety of crops around the world [1]
Residue levels of thiamethoxam analysed in bee bread stored in cells were lower than or equal to pollen collected from foraging bees, being at or below the 1 mg/kg limit of quantification (LOQ)
In the paper by Schneider et al [20], no adverse effects were observed when bees were exposed to imidacloprid or clothianidin at field-relevant doses; effects on foraging activity were only recorded at higher doses
Summary
Honey bees provide a vitally important role, both ecologically by pollinating wild plants, and economically by providing a pollination service to a variety of crops around the world [1]. Numerous studies have reported a decline in honey bee health and numbers of colonies in recent years [2,3]. Many factors may have contributed to this decline in health, for example the spread of parasites and pathogens [6], reduction in available forage [7], beekeeping management practices (for example Varroa destructor control and the development of resistance to treatments), movement of colonies, weather and climate change [8]. Exposure to certain pesticides is another factor that has been implicated in bee health decline [9]. The use of neonicotinoid insecticides in crops where bees forage has been reported as a potentially contributing factor [10,11]
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