Limiting resources on the reproductive success of a cavity-nesting bee species in a grassland agroecosystem

Abstract

Intensive agricultural land use can impact pollinators mainly through habitat loss and/or modification. Native bees are negatively affected by agricultural intensification, isolation from natural habitats, decreases in plant diversity, and reduction in the availability of nesting sites. Despite this, in the Pampean region, there are scarce studies about the effect of agricultural activities on native bees. We studied the nesting ecology of the native leafcutter bee Megachile gomphrenoides (Megachilidae) in eight sites immersed in an agricultural matrix, where land use is a mosaic of agricultural land and some semi-natural areas. The sampling was developed using paired trap-nests in fragments without agricultural management and in soybean crops. We aimed to analyse the effects of floral and nesting resources on the abundance, the reproductive success and the parasitism rate of a population of M. gomphrenoides in a Pampean agroecosystem. Floral diversity was significantly correlated with abundance of nests and brood cells, and both parasitism rate and reproductive success of M. gomphrenoides were higher in nests built in fragments without agricultural management when compared to crop areas. Additionally, a negative correlation was found between reproductive success and flower diversity in crop areas. These results suggest that floral diversity is limiting the abundance of M. gomphrenoides nests, its reproductive success as well as its parasitism rate.