Revealing the diversity of wild bees (Hymenoptera: Apoidea: Anthophila) in flower strips in Mediterranean floodplains: which monitoring method fits best?

The ongoing pollinator decline may threaten and compromise the resilience of terrestrial ecosystems. Implementing conservation action requires monitoring pollinator populations. Since more than 55% of European bee species are classified as “Data Deficient” by the IUCN, monitoring their populations is very important. However, although crucial, the results of bee monitoring are strongly dependent on the applied methods. Here, we compared different monitoring methods to evaluate wild bee biodiversity in lowland areas enriched with entomophilous flowers to support pollinating insects in a Mediterranean environment. We sampled wild bees for two years using hand netting, pan traps and artificial nests. We compared species richness and abundance among these methods with a particular focus on how flowering coverage affects the results of walking transects and pan traps and discussed the attractiveness of the different colours of pan traps. Hand netting captured a higher number of wild bee specimens and species than the other two methods. Artificial nests captured fewer specimens and species. Bee assemblages were significantly different between pan traps and hand netting and pan trap attractiveness was negatively influenced by the increase of flowering coverage. As for other studies, the three sampling methods were complementary in reaching the final species assemblages and although time-consuming, the juxtaposition of several monitoring methods appears essential to reveal species with different ecological traits.