Autumn intermediate crops and development of honey-bee colonies

Establishing an autumn vegetation cover following the grain harvests is common practice in the farming community. Although certain beekeepers look forward to this foraging opportunity, others suspect a weakening of the bee colonies after they forage on these cover crops, and fear the premature exhaustion of the winter bees. The experiment presented here attempts to evaluate whether late foraging weakens or stimulates the colonies before winter, and whether it has an impact on overwintering. It also aims to determine whether the intermediate crops established directly after a straw cereal coated in neonicotinoids may represent a potential danger for bees. The study shows that foraging on intermediate crops has neither an adverse nor a positive effect on bee populations during flowering and in the following months. Moreover, winter losses are no greater. Chemical analyses show that neonicotinoids may be present in the soil whatever the treatment of the previous crop, and that traces are sometimes found in the pollen brought back to the hive, as well as in the bee bread. These conditions prevent us from comparing two groups with clear different exposures, which would allow us to test the effect of the neonicotinoids in the previous crop on the colonies.

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