CONICET | Buscador de Institutos y Recursos Humanos

Bee decline is a major concern due to their vital role in pollinating many crops and wild plants. This region has been intensively transformed for agriculture, being presently one of the most productive areas of agricultural commodities in the world. Here, we aim to provide first insights on the taxonomical and functional composition of bee assemblages in the Rolling Pampa, the most intensively managed part of the Pampas, and the corn-belt of Argentina. Soybean (herbicide tolerant genetically modified varieties) is the predominant crop in this region. Bees were sampled with colored pan traps during three different periods of the warm season. Sampling points were located on field margins either in the cropped or the semi-natural grassland area of a farmland site devoted to annual cropping. A total of 2384 wild bee individuals were caught, representing 33 taxa (mainly species and morphospecies). The subgenus Lasioglossum (Dialictus) largely dominated captures (78% of the total abundance) and was relatively abundant in the entire study area, suggesting that some species of this group are likely to reach their ecological requirements in cropped areas. No-tilled fields probably provide large areas for below-ground nesting species, while their polylectic food preferences allow them to collect pollen on a wide range of plant species, among them possibly soybean. On the contrary, the richness and the abundance of other taxa were higher in the semi-natural area than in the cropped area. Above-ground nesting, oligolectic, or oil-collecting species were scarce and largely rely on the nesting and food resources provided by the semi-natural area to survive. Our findings highlight (1) the large dominance of Lasioglossum (Dialictus) species in this highly intensively managed landscape, and (2) the urgent need of preserving semi-natural habitats to maintain species-rich and functionally diverse bee communities in the Pampas.