BEES AND WASPS IN A CHANGING ENVIRONMENT: MULTIPLE RESPONSES TO ANTHROPISED LANDSCAPES

Bees and predatory wasps provide highly relevant ecosystem services, the former being the main pollinator group and the latter regulating arthropod populations. Anthropisation, the way in which human activities shape natural ecosystems, threatens these insects from the community to the individual level. However, little is known about intraspecific shifts in morphological, physiological, behavioural, and ecological functional traits (i.e. those important for the health and fitness) of bees and wasps in response to anthropisation. The aim of this project was to understand how two different anthropogenic disturbances affect functional traits in bees and wasps: urbanisation and agricultural practices. Urbanisation, which leads to increased temperature and impoverishment and fragmentation of vegetated areas, was investigated in the Metropolitan City of Milan (Northern Italy). The use of sewage sludge, which may contain toxic trace elements, as agricultural soil amendment was studied in the Parco Adda Sud (Northern Italy). Five target species were considered: the bees Anthophora plumipes Pallas, 1772 (Hymenoptera: Apidae), Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae), Halictus scabiosae (Rossi, 1790) (Hymenoptera: Halictidae) and Osmia cornuta (Latreille, 1805) (Hymenoptera: Megachilidae), and the wasp Polistes dominula (Christ, 1791) (Hymenoptera: Vespidae). The field studies were preceded by a re-analysis of published data on wild bee communities in different cities around the world, which showed how highly urbanised areas filter for bee species with specific functional traits (social, polylectic, above-ground nesting). The predicted effects on morphology, physiology and behaviour at the intra-specific level were instead formalised in a dedicated opinion paper. With field observations, microscopy techniques, histological observations, and chemical and genetic analyses investigations, I have found that urbanisation affected many of the considered functional traits, albeit often with species-specific patterns. Morphologically, smaller individuals (H. scabiosae, O. cornuta, and P. dominula) as well as individuals with a longer galea (A. plumipes), better flight-related wing characteristics (H. scabiosae, O. cornuta, and P. dominula) and higher values of wing fluctuation asymmetry (a proxy for larval developmental stress) (A. plumipes, H. scabiosae, and P. dominula) were found in hotter and more fragmented urban areas. Furthermore, O. cornuta (in more fragmented urban areas) and A. plumipes (in hotter urban areas) appeared to have a visual sensory system that probably improves image resolution, while O. cornuta (in hotter urban areas) additionally reduced resource investment in cold-adapted thermoreceptors. Finally, one species (H. scabiosae) showed greater histological damage to the midgut epithelium in urban areas with higher road cover, while P. dominula showed a reduced yellow pigmentation in hotter urban areas. Physiologically, hotter urban areas increased the mean chain length of the cuticular hydrocarbon profile of O. cornuta and the relative abundance of some long chain n-alkanes in H. scabiosae and P. dominula. In addition, A. mellifera from hotter and less green urban areas showed reduced activity of Aminopeptidase N, a proteolytic enzyme. Finally, hotter urban areas reduced the abundance of some bee viruses in A. plumipes and O. cornuta, while fragmentation increased the presence of the protozoan Apicystis bombi in A. plumipes, O. cornuta, and P. dominula. Behaviourally, hotter areas increased the aggressiveness of O. cornuta females towards conspecifics. Finally, urbanisation seemed to provide key habitats for the shift in the geographical distribution of H. scabiosae over the recent decades. Sewage sludge has been found to contain the known toxic elements Cd, Pb and Hg, among other trace elements. Apis mellifera with higher levels of Pb were smaller, those sampled from sites with high levels of Hg had higher fluctuating asymmetry and more histological damage to the midgut epithelium, and those sampled from sites with higher levels of Cd had higher carbohydrate content. Overall, these studies have important conservation implications. Temperature is a crucial factor in determining morpho-physiological changes in bees and wasps in urbanised areas. Improving green areas would likely mitigate these higher temperatures. This would also counteract other detrimental elements of the urban matrix: the reduction and fragmentation of green spaces. The spatial configuration of green areas plays a key role in affecting bees and wasps. In particular, the creation of ecological corridors and the reduction of mowing regimes could certainly bring benefits in terms of trophic and nesting resources for these insects. Overall, these practices could also have positive effects at a community level, possibly sustaining functionally diverse bee and wasp communities. Regarding the practice of sewage sludge use, this study highlighted the possible negative effects of this practice and the need to include ecotoxicological tests on model animal organisms to authorise the spreading of the sludge. Future studies should consider the genetic basis of the observed variation to clarify whether the observed phenotypic shifts are the result of phenotypic plasticity or genetic adaptation. In addition, other biological aspects of bees and wasps should be investigated, such as the effects of anthropisation on the gut microbiome, the food resources or the nesting choices of these insects.