Diversity loss of spider-hunting wasp (Hymenoptera: Pompilidae) induced by soybean fields in Brazilian Amazon, Cerrado, and in transitional zones

The expansion of agricultural fields has driven biodiversity loss. As such, this process requires further investigation given its potentially catastrophic impacts on native fauna. In this study, we investigated the effects of converting native habitats into soybean fields on the species richness and composition of spider wasps (Hymenoptera: Pompilidae) in the Amazon, Cerrado, and Transitional Zones. We sampled spider wasps at 100 agricultural landscapes throughout a region encompassing Amazon forests, Cerrado savannahs, and a transitional vegetation domain in Mato Grosso, Brazil. Specimens were collected in native habitats, edges, and soybean fields using malaise traps. In total, we recorded 436 wasps of 94 species. Habitat type influenced both richness and species composition. Native habitats and edges did not differ in species richness, but both showed higher richness than soybean fields. At the habitat scale, species shared with soybean fields were low (< 3%). Among the restricted species, 23 were found only at edges (24.5%), 17 only in native habitats (18.1%), and 19 only in soybean fields (20.2%). At the vegetation-domain scale, species exclusivity was highest in the Amazon with 33 species (35.1%), followed by the Cerrado with 18 species (19.1%), and the Transition zone with six species (6.4%). These findings reflect two complementary patterns. First, the high dissimilarity among vegetation domains indicates major differences in species composition across regions. Second, within each domain, species shared among soybean fields and other habitats remained low, suggesting limited overlap in species composition at the habitat scale. Although a subset of Pompilidae can exploit floral resources and hosts within agricultural matrices, our results revealed low species sharing among habitats and a considerable number of habitat-restricted species. This pattern indicates that most species remained strongly associated with native habitats and edges. Therefore, native habitats are essential for maintaining regional Pompilidae diversity, and locally focused conservation strategies, such as preserving forest and savannah remnants and enhancing ecological connectivity, are necessary to mitigate the impacts of monoculture expansion on wasp assemblages.