Pollinators in a changing world: long term variations and pesticide pressure in agricultural systems

Insect pollinators are fundamental in sustaining biodiversity and human well-being by providing pollination services to nearly 90% of flowering plant species. However, their populations are increasingly threatened by environmental changes driven by human activities, such as urbanization and agricultural intensification. Among insect pollinators, bees are the most important group in terms of abundance and effectiveness, ensuring pollination for approximately 75% of crops. Despite their crucial ecological and economic importance, significant knowledge gaps remain for 14% of bee species, while 10% of them are recognised as threatened. Long-term studies are therefore essential to investigate species distribution across time and space. Therefore, entomological collections represent a valuable resource for obtaining information on species occurrence and assessing changes in ecological traits. Alongside, many studies have highlighted the role of pesticides in the decline of pollinators. Among these, fungicides and insecticides, either alone or in combination, are toxic to many of them, while herbicides reduce the availability of food resources. Orchards and other crop systems are the environments where pollinators are mostly exposed to pesticides, although these compounds can spread through the environment and contaminate natural resources. However, the role of pesticide exposure via wild plants near cultivated areas remains unclear. At the same time, information concerning pollination deficits, as a consequence of pollinator decline, is limited to few crops. The aims of this thesis are: to evaluate the variation of pollinator community, in terms of species richness and functional diversity, in northern Italy through a comparison with a historical entomological collection, (Chapter 1); to assess pesticide contamination in crop and wildflowers in apple orchard, a widespread European crop system, and the potential risk posed to pollinators (Chapter 2); to assess pollination deficits in an important and understudied European crop, Pyrus communis, in relation to pollinator communities, landscape characterization and pesticide risk (Chapter 3).