Bee populations have decreased in recent decades mainly due to a loss of biodiversity causing the decline of their essential host plants, according to a study published Monday in the journal US Proceedings of the National Academy of Sciences (PNAS). The scientists of Wageningen University in The Netherlands analysed the pollen found on the bodies of insects from 57 different wild bee species collected before the onset of their decline and used data to quantify population trends of bee species and their host plants. They found that the bees had certain favoured plants for pollinating. Dr Jeroen Scheper, an environmental specialist at the Alterra Research Institute reported, “we assessed the relative importance of a range of proposed factors responsible for wild bee decline and show that loss of preferred host plant species is one of the main factors associated with the decline of bee populations in The Netherlands”. Another important factor was bee body size, because larger bee species require more pollen to survive than smaller species. The researchers said that diet breadth and other potential factors such as length of flight period or climate change sensitivity were not important in explaining twentieth century bee population trends. The loss of natural habitats, namely grasslands, that are increasingly used for intensive agricultural production has led to a decline in wildflowers and the loss of bees’ food sources. Scheper mentions, that “these results indicate that mitigation strategies for loss of wild bees will only be effective if they target the specific host plants of declining bee species”. Bees are important for crop production, pollinating up to 80% of plants and flowers essential to the human diet.