Agricultural intensification favors dominant species while changing pollinator community compositions in a subtropical watershed of Uruguay

Sheena Marie Salvarrey^1,2*Loreley Castelli³Ciro Invernizzi¹Yulai Ramos¹Eugenia Suárez⁴Joaquín Aldabe⁴Gabriela Bentancur⁵Juan Pablo Burla⁴Mónica Remedios⁵Ismael Díaz⁶Camila Fernández-Nion⁷Estela Santos¹Franco Teixeira de Mello⁸Natalia Arbulo⁴

• ¹Section of Ethology Faculty of Sciences, University of the Republic, Montevideo, Uruguay
• ²Universidad de la Republica Uruguay Facultad de Ciencias, Montevideo, Uruguay
• ³Laboratorio de Microbiología y Salud de las Abejas, Departamento de Microbiología, Instituto de Investigaciones Biologicas Clemente Estable, Montevideo, Uruguay
• ⁴Departamento de Sistemas Agrarios y Paisajes Culturales, Universidad de la Republica Uruguay - Centro Universitario de la Region Este - Sede Rocha, Rocha, Uruguay
• ⁵Sección Entomología, Universidad de la Republica Uruguay Facultad de Ciencias, Montevideo, Uruguay
• ⁶6Laboratorio de Desarrollo Sustentable y Gestión Ambiental del Territorio, Instituto de Ecología y Ciencias Ambientales,, Universidad de la Republica Uruguay Facultad de Ciencias, Montevideo, Uruguay
• ⁷Laboratorio de Desarrollo Sustentable y Gestión Ambiental del Territorio, Instituto de Ecología y Ciencias Ambientales, Universidad de la Republica Uruguay Facultad de Ciencias, Montevideo, Uruguay
• ⁸Departamento de Ecología y Gestión Ambiental., Universidad de la Republica Uruguay Centro Universitario de la Region Este - Sede Maldonado, Montevideo, Uruguay

The current pollination crisis underscores the urgent need for enhanced research and monitoring efforts on pollinator diversity, as well as the development of effective strategies to promote their conservation. In Uruguay, soybean cultivation has expanded by approximately 1,000% in the last 20 years, and monocultures and pesticide use threaten pollinator food and nesting resources. However, data on native pollinators remain limited. In this study, the abundance and composition of pollinating insects were assessed in the San Salvador River basin, one of the country's main agricultural areas, using color pan traps installed at six paired sites (cultivated vs. wild vegetation) over three seasons (summer 2022, spring 2022, and summer 2023). To assess the effects of land use and sampling season on insect diversity, two approaches were employed: insect abundance was analyzed using generalized linear mixed models (GLMMs), and community composition at the order and morphospecies levels was evaluated using the Bray–Curtis index. A total of 10,690 insects, belonging to the main orders of Hymenoptera, Diptera, Lepidoptera, and Coleoptera, which include pollinators, were identified. Total insect abundance was significantly higher in cultivated sites than in wild sites. This association was also observed in Coleoptera, although this group exhibited an interaction with the sampling season, with the most abundant numbers being observed in both summers. Beta diversity (Bray-Curtis) revealed significant differences by land use and season at the order and morphospecies levels. Land use appears to be the variable associated with differences in insect communities across the evaluated sites. Particularly noteworthy is the species A. atromaculatus (Coleoptera) which presented much higher abundances than all other taxa. These results provide new insights into the structure of pollinator communities in agroecosystems and highlight the need to incorporate them into sustainable production, monitoring, and conservation efforts in the region.