Abstract
Insecticide-treated cotton seeds can pose risks to Apis mellifera Linnaeus, 1758 populations during crop establishment if chemical residues reach these insects near agricultural fields via dust drift produced during planting. However, the treatment of seeds with insecticides is essential to protect cotton plants from damage caused by pests, including thrips and aphids. Thus, the aim of this study was to evaluate the toxic effects (acute toxicity) of soil dust from cotton fields planted with insecticide-treated seeds on A. mellifera adults using a toxicity assay developed in the laboratory. Forager honeybees were maintained in 700-ml plastic cages with 7 g of surface soil where insecticide-treated cotton seeds were sown (270 g a.i. clothianidin, 270 g a.i. imidacloprid, 210 g a.i. thiamethoxam, and 75 g a.i. fipronil/100 kg of seeds, and an untreated group). Ten bees were placed in each cage. The experimental design was randomized, with five treatments and twelve replicates. The mortality rate was evaluated during the entire assay. Data were transformed to x + 0.5  and compared with a regression analysis and contrast test. The linear regression model revealed a significant relationship between bee mortality and exposure time. The mortality rate gradually increased as time progressed in all treatments and the control group. The contrast test did not reveal significant differences between the insecticide and control groups. Thus, residues of the products tested, thiamethoxam, clothianidin, imidacloprid, and fipronil, did not influence the mortality of A. mellifera adults as a result of exposure to soil contaminated with insecticide-treated seeds.
Highlights
Cotton is widely used by industries worldwide and is a fundamental commodity to the primary and secondary sectors
The neonicotinoids, clothianidin, imidacloprid, thiamethoxam, and fipronil have been considered potential factors associated with Colony Collapse Disorder (CCD), characterized by the sudden disappearance of worker bees and weakening of colonies
Large areas planted with treated seeds combined with the high persistence of pesticide residues and soil mobility might have negative effects on beneficial organisms, including plants near agricultural fields (Krupke et al, 2012). Since these pesticides could be associated with CCD, and residues have been found in the soil, the aim of the present study was to evaluate the effects of insecticide-contaminated soil collected near where treated seeds were sown on A. mellifera bees, by developing a laboratory bioassay based on bee mortality to evaluate insecticide residue in the soil after sowing
Summary
Cotton is widely used by industries worldwide and is a fundamental commodity to the primary and secondary sectors. Neonicotinoids efficiently control the main pests of cotton, such as the boll weevil, Anthonomus grandis Boheman 1843 (Fonseca et al, 2011), aphids, thrips, and whiteflies (Torres et al, 2004; Andrei, 2013). These insecticides may affect important beneficial insects for this crop, such as pollinators. The neonicotinoids, clothianidin, imidacloprid, thiamethoxam, and fipronil have been considered potential factors associated with Colony Collapse Disorder (CCD), characterized by the sudden disappearance of worker bees and weakening of colonies. It is unclear if a single factor is consistently or sufficiently abundant in CCD-affected colonies to be identified as the causative agent (van Engelsdorp et al, 2009)
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