Abstract
Abstract The effects to honeybee colonies (Apis mellifera L.) during and after exposure to flowering maize (Zea mays L.), grown from seeds coated with clothianidin and imidacloprid was assessed in field-realistic conditions. The experimental maize crops were adjacent to the other flowering agriculture plants. Honey bee colonies were placed in three differently protected maize fields throughout the blooming period, and thereafter they were transferred to a stationary apiary. Samples of pollen loads, bee bread, and adult bees were collected and analyzed for neonicotinoid residues. To ensure high specificity and sensitivity of detection of the analyzed pesticides, a modified QuEChERS extraction method and liquid chromatography coupled with tandem mass spectrometry were used. Clothianidin was detected only in the samples of pollen loads. Their residue levels ranged from 10.0 to 41.0 ng/g (average 27.0 ng/g). Imidacloprid was found in no investigated sample. No negative effects of neonicotinoid seed-treated maize on the development and long-term survival of honey bee colonies were observed. The low proportion of Zea mays pollen in total bee-collected pollen during the maize flowering period was noted. The findings suggest that maize plants are less attractive forage for honey bees than phacelia (Phacelia tanacetifolia Benth.), buckwheat (Fagopyrum Mill.), white clover (Trifolium repens L.), goldenrod (Solidago L.), and vegetation from Brassicaceae family. The results indicate a possibility of reducing the risk of bees being exposed to the toxic effect of insecticidal dusts dispersed during maize sowing by seeding, in the areas surrounding maize crops, plants that bloom later in the year.
Highlights
Pesticides applied to crops are considered a significant factor in the decline of pollinators, of which honey bees are the most important species
This hypothesis is partly confirmed by monitoring of honey bee colonies which shows that bee-collected plant material and bee products such as honey, bee bread, and beeswax contain residues of many pesticides
Residue analysis Of the two neonicotinoid insecticides used for protecting maize crops, only the clothianidin was found in the examined material
Summary
Pesticides applied to crops are considered a significant factor in the decline of pollinators, of which honey bees are the most important species. Neonicotinoid seed treatment is a relatively new, modern technology, which confers many advantages: it is very efficient, dosages needed are low, it provides long-lasting protection, and it requires a relatively limited number of insecticide sprays (EFSA, 2012) Neonicotinoids such as imidacloprid, clothianidin, and thiamethoxam are extremely toxic to bees with lethal and sublethal effects depending on the level of exposure. In North America, where at least 94% of the 36 million hectares planted with maize is treated with clothianidin or thiametoxam, those crops are considered a major source of neonicotinoid exposure for bees living near agricultural fields (Krupke et al, 2012) It remains unclear whether neonicotinoid seed-treated maize has side-effects on honey bees when bee-attracting plants in the adjacent areas do not bloom during the time of maize sowing. Methods involved determining the level of neonicotinoid residues in bee-collected pollen and bee bread; exploring the use of maize forage by bee colonies; and evaluating the short- and long-term impact of possible residues on the health status of bee colonies
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