Floral Resources Used by Honey Bees in Agricultural Landscapes

Abstract

Honey bees are polylectic insects able to forage on many flower species in order to provide enough abundant and diverse food for the colony. However, land use changes and agricultural intensification have disrupted the floral availability in agricultural landscapes. Here, we investigated empirically the floral resources used by honey bees in an intensive cereal farming system. We found that honey bees foraged on a wide diversity of flowers throughout the season, mainly derived from trees and weeds. When mass-flowering crops are available, honey bees use them. However, mass-flowering crops are highly seasonal and induce a supply depletion between two peak periods, which precisely matches the peak of demographic growth of bee colonies. Our empirical results support the Agri-Environmental Schemes intended to promote honey bees and beekeeping sustainability. The Long-Term Ecological Research “Zone Atelier Plaine et Val de Sèvre” in central western France (46°23' N, 0°41' W) hosts a study about bee ecology since 2008 through the ECOBEE platform. Local agricultural intensification has led to an intensive cereal farming system, with mass-flowering crops such as rapeseed (Brassica napus) and sunflower (Helianthus annuus). In this environmental context, we studied the foraging behavior of honey bees throughout the beekeeping season with 250 monitored colonies. Photo by Christophe Maitre/INRA. We fitted beehives with pollen grid traps at their entrance in order to sample the pollen loads harvested by foragers. This photo shows the variability of colors in collected pollen loads, witnessing the diversity of flowers visited by honey bees. In our intensive agricultural landscape, honey bees forage on a wide diversity of flowers for their pollen intakes (about 230 species). Photo by Thierry Tamic. We identified the botanical origin of pollen loads by palynological analyses. We present here the pollen grains of the three dominant floral resources used by honey bees in intensive cereal farming system, i.e. two crops, maize (Zea mays, the big pollen grain at center), and sunflower (the smaller echinate pollen grains), and a weed species, poppy (Papaver rhoeas, bottom right). The changing dynamic of crop flower availability disturbs the seasonal pattern of pollen intake with pollen supply depletion in spring. Surprisingly, poppy is a dominant species foraged for pollen in similar proportion than maize and sunflower. Poppy is especially collected during the period of pollen supply depletion, indicating a major role of weeds for honey bee diet in intensive cereal farming systems. Photos by Thierry Tamic. Honey bees forage on a wide diversity of flowers in intensive agricultural landscapes. For example, we present here four plant species foraged by honey bees for pollen and/or nectar intakes, i.e. Prunus spinosa (top left) a woody plant species foraged in April; Bellis perennis (top right) a herbaceous plant species foraged throughout the whole season; Malva sylvestris (bottom left) a herbaceous plant species foraged in July; and Phacelia tanacetifolia (bottom right) a crop foraged in May. Semi-natural habitats (i.e. grasslands, forest, and hedgerows) and weeds need to be considered for bee conservation in agricultural landscapes because they provide highly diverse and continuous floral resources throughout the season. Photos top left and bottom left by Thierry Tamic, and photos top right and bottom right by Fabrice Requier. These photographs illustrate the article “Honey bee diet in intensive farmland habitats reveals an unexpectedly high flower richness and a major role of weeds” by Fabrice Requier, Jean-François Odoux, Thierry Tamic, Nathalie Moreau, Mickaël Henry, Axel Decourtye and Vincent Bretagnolle, published in Ecological Applications 25(4):881–890, June 2015. http://dx.doi.org/10.1890/14-1011.1