Exposure to pollen-bound pesticide mixtures induces longer-lived but less efficient honey bees.

Due to the widespread use of pesticides and their persistence in the environment, non-target organisms are chronically exposed to mixtures of toxic residues. Fungicides, herbicides and insecticides are all found at low doses in the diet of pollinators such as honey bees, but due to the lack of data on the toxicological effects of these mixtures, determining their risk is difficult to assess. We therefore developed a study combining the identification of common pollen-bound pesticide mixtures associated with poor colony development and tested their effects on bee behavior and physiology. We exposed bees to the identified pesticide mixtures during the first days of their adult life, a crucial period for physiological development. Using optic bee counters we recorded the behavior of bees throughout their lives and identified two pesticide mixtures that delay the onset of foraging and slow-down foraging activity. Furthermore, one of these mixtures hampers pollen foraging. As bee longevity is strongly influenced by the time spent foraging, bees exposed to these pesticide mixtures outlived control bees. Physiological analysis revealed that perturbations of the energetic metabolism preceded the altered behavior. In conclusion, we found that early-life exposure to low doses of pesticide mixtures can have long-term effects that translate into longer-lived but slower and less efficient bees. These surprising findings contrast with the commonly reported increase in bee mortality upon pesticide exposure, and demonstrate that exposure that may seem harmless (e.g., very low doses, pesticides not intended to kill insects) can have undesirable effects on non-target organisms.

Influence of pollen nutrition on honey bee health: do pollen quality and diversity matter?

Honey bee colonies are highly dependent upon the availability of floral resources from which they get the nutrients (notably pollen) necessary to their development and survival. However, foraging areas are currently affected by the intensification of agriculture and landscape alteration. Bees are therefore confronted to disparities in time and space of floral resource abundance, type and diversity, which might provide inadequate nutrition and endanger colonies. The beneficial influence of pollen availability on bee health is well-established but whether quality and diversity of pollen diets can modify bee health remains largely unknown. We therefore tested the influence of pollen diet quality (different monofloral pollens) and diversity (polyfloral pollen diet) on the physiology of young nurse bees, which have a distinct nutritional physiology (e.g. hypopharyngeal gland development and vitellogenin level), and on the tolerance to the microsporidian parasite Nosemaceranae by measuring bee survival and the activity of different enzymes potentially involved in bee health and defense response (glutathione-S-transferase (detoxification), phenoloxidase (immunity) and alkaline phosphatase (metabolism)). We found that both nurse bee physiology and the tolerance to the parasite were affected by pollen quality. Pollen diet diversity had no effect on the nurse bee physiology and the survival of healthy bees. However, when parasitized, bees fed with the polyfloral blend lived longer than bees fed with monofloral pollens, excepted for the protein-richest monofloral pollen. Furthermore, the survival was positively correlated to alkaline phosphatase activity in healthy bees and to phenoloxydase activities in infected bees. Our results support the idea that both the quality and diversity (in a specific context) of pollen can shape bee physiology and might help to better understand the influence of agriculture and land-use intensification on bee nutrition and health.