Abstract
Intensive agricultural systems often expose honey bees (Apis mellifera L.) to large temporal variations in the availability (quantity, quality and diversity) of nutritional resources. Such nutritional irregularity is expected to affect honey bee health. We therefore tested under laboratory conditions the effect of such variation in pollen availability on honey bee health (survival and nursing physiology—hypopharyngeal gland development and vitellogenin expression). We fed honey bees with different diets composed of pollen pellets collected by honey bees in an agricultural landscape of western France. Slight drops (5–10%) in the availability of oilseed rape (Brassica napus L.) pollen resulted in significant reductions of all tested variables. Despite some variations in taxonomic diversity and nutritional quality, the pollen mixes harvested over the season had a similar positive influence on honey bee health, except for the one collected in late July that induced poor survival and nursing physiology. This period coincided with the mass-flowering of maize (Zea mays L.), an anemophilous crop which produces poor-quality pollen. Therefore, changes in bee health were not connected to variations in pollen diversity but rather to variations in pollen depletion and quality, such as can be encountered in an intensive agricultural system of western France. Finally, even though pollen can be available ad libitum during the mass-flowering of some crops (e.g. maize), it can fail to provide bees with diet adequate for their development.
Highlights
Bee species can be classified into two broad categories regarding their pollen diet: specialists, that feed on a few or even a single plant species, and generalists, that forage on a large array of phylogenetically unrelated plant species [1]
We tested under laboratory conditions the effect of such variation in pollen availability on honey bee health
Despite some variations in taxonomic diversity and nutritional quality, the pollen mixes harvested over the season had a similar positive influence on honey bee health, except for the one collected in late July that induced poor survival and nursing physiology
Summary
Bee species can be classified into two broad categories regarding their pollen diet: specialists, that feed on a few or even a single plant species, and generalists, that forage on a large array of phylogenetically unrelated plant species [1]. Pollen Availability and Honey Bee Health intensification of agriculture often causes a decrease in the diversity of floral resources due to the destruction of natural habitats and the use of monocultures over large areas, but it affects the quantity of resources available because the flowering period of a crop is usually short [6] Such changes in the landscape and in spatial and temporal availability of foraging resources can influence colonies as it has long been recognized that a lack of food, in particular pollen dearth, contributes to weaken colonies [7,8]. The diversity of pollen species harvested by honey bee colonies shows considerable temporal variations [6,38,39] It is not known whether and how the variability of available pollen resources (quantity, quality and diversity) encountered by honey bees in an agricultural landscape influences their health. Vitellogenin is a multifunctional lipoprotein [43] synthetized in the fat body, acting as an antioxidant to promote longevity in both queen and workers [44,45], and it is used by nurses for the production of brood food [43,46]
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