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More than 900 species of wild bees are found in France, but many of them — such as bum­ble­bees — are in decline. Sci­en­tists from the French National Insti­tute for Agri­cul­tural Research (INRA), work­ing in col­lab­o­ra­tion with the nat­u­ral­ist asso­ci­a­tion Arthro­polo­gia, have car­ried out the first exhaus­tive study in Europe to eval­u­ate the impact of urban­i­sa­tion on the wild bee com­mu­nity. They stud­ied 24 more or less urbanised sites in and around Lyon and recorded 291 dif­fer­ent bee species. Although bee abun­dance decreased with an increas­ing level of urban­i­sa­tion, the num­ber of species present was at its peak in peri­ur­ban areas, and 60 species — a con­sid­er­able num­ber — were found at the most urban site. These find­ings are pub­lished in the open-​access jour­nal PLOS ONE on 13 August.

For a bee species to be present in an urban envi­ron­ment, it must be able to find suf­fi­cient food resources and appro­pri­ate nest­ing sites. Some bee species are ground-​nesting, such as min­ing bees, while oth­ers (such as mason bees, Osmia species) nest in pre-​existing cav­i­ties. Aside from its nest­ing behav­iour, each bee species has its own bio­log­i­cal char­ac­ter­is­tics and may there­fore respond dif­fer­ently to urban­i­sa­tion. The dif­fer­ent species and their char­ac­ter­is­tics then become essen­tial ele­ments to study the impact of urban­i­sa­tion on the struc­ture of wild bee com­mu­ni­ties, defined as all the species found in a given environment.

In the con­text of the Euro­pean LIFE Urban­bees pro­gramme, wild bee com­mu­ni­ties were stud­ied at 24 sites along an urban­i­sa­tion gra­di­ent in the Urban Com­mu­nity of Lyon. Every month for two years, bees were sam­pled using coloured pan traps and insect nets at the 24 sites around Lyon. The pan traps were left active for 24 hours. The nets were used to cap­ture insects on all flow­er­ing plants within a radius of 100 metre from the traps. In order to study changes in the com­po­si­tion of the com­mu­nity, the sci­en­tists took into account dif­fer­ent bee char­ac­ter­is­tics: host/​parasite sta­tus and nest­ing mode.

In this study, 291 species of wild bee were cap­tured, or almost a third of the more than 900 wild bee species known in France. Bee abun­dance was neg­a­tively cor­re­lated with urban­i­sa­tion, but species rich­ness reached its max­i­mum in sites at an inter­me­di­ate pro­por­tion of urban­i­sa­tion (called the peri­ur­ban envi­ron­ment). Nev­er­the­less, sci­en­tists found con­sid­er­able rich­ness in the most urbanised areas (60 species in Villeur­banne at a site with over 98% of impen­e­tra­ble sur­face area for bees). The struc­ture of the com­mu­nity changed along the urban­i­sa­tion gra­di­ent, with more par­a­sitic species in peri­ur­ban envi­ron­ments. Cavity-​nesting bees were more diver­si­fied in urban envi­ron­ments than ground-​nesting bees.

Bees on a sun­flower in Parc de la Tête d’Or, Lyon

(Source: Gra­ham Miln YouTube channel)

The con­sid­er­able diver­sity of wild bees recorded in the city cen­tre showed that through appro­pri­ate man­age­ment, even the most urban areas could be inter­est­ing envi­ron­ments in terms of ecol­ogy and con­ser­va­tion in order to safe­guard these pol­li­na­tors and the mutual rela­tion­ship they main­tain with wild and cul­ti­vated plants. The diver­sity of wild bees in cities also means they con­sti­tute a flag­ship group to raise the aware­ness of urban pop­u­la­tions to ecol­ogy and ecosys­tem ser­vices, show­ing them that bio­di­ver­sity can be encoun­tered every­where and on an every­day basis.

(Source: INRA press release, 14.08.2014)