Floral resources: to each bee his own

Bees use floral resources differently depending on what bee family they belong to, such as honeybees, wild bees or bumblebees. This new discovery was made by researchers from the Bees and the Environment Unit at the INRA PACA centre, in cooperation with the Itsap Institut de l’abeille. The study was the basis of an article in the scientific journal Agriculture, Ecosystems and Environment and a note by the European Commission’s Directorate General for the Environment early this year.

Bee on Cistus ladanifer. © INRA, Nicolas Morison

This study of the pollen gathering behaviour of bees follows a thesis carried out under the Polinov research project. The project aims to design innovative cropping systems that promote both sustainable agriculture and help protect bees and their environment. One of its specific goals is to make recommendations for agro-environmental measures.

30,000 bees studied over three years

The study focused on the three groups of bees that European agro-environmental measures aim to help: honeybees (Apis mellifera), wild bees and bumblebees (Bombus sp.).  Researchers analysed areas where these three groups are found: semi-natural habitats with little human intervention, such as prairies or hedges, and flowering crop fields planted with rapeseed (Brassica napus), sunflower (Helianthus annus) and alfalfa (Medicago sativa).

Bees’ pollen gathering activity was quantified using surveillance and bee capture. This made it possible to establish the presence, abundance or absence of the three bee groups at the various selected sites. This ‘census’ was carried out over three years at 812 sites spread over a 500km2 swath of cropland used for research, the Zone Atelier Plaine et Val de Sèvre in Poitou-Charentes. More than 30,000 pollen gathering bees were counted and monitored.

Differing pollen gathering behaviours

The results showed that honeybees like to gather pollen from flowering crops, while wild bees prefer the more diverse native flowers from semi-natural habitats as their food source. Why the difference? Honeybees live in colonies of thousands of bees that must be fed. Oilseed crops, which produce a large number of flowers over a short period of time, are a top meal choice. Another working theory, not unrelated to the first, is that the difference is due to selection over time by apiculturists from the most productive colonies – and therefore the most efficient pollen gatherers. Some wild bees are specialised gatherers, gathering pollen from a single type of wild plant. They are generally solitary bees and do not store nectar like honeybees do. This is the case for Andrena florea, which depends on pollen from the Bryony plant.

Bumblebees have a food strategy that falls somewhere between that of honeybees and wild bees. They gather pollen from both flowering crops and natural habitats to create reserves for their colony.

Although bee populations have declined over the past several years, caused in part by intensified farming, the study suggests that the combination of flowering crops and semi-natural habitations in the agro-environmental programmes would be beneficial to the three groups of bees studied.

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