No Vertical Stratification Found in Cavity-Nesting bees and Wasps in Two Neotropical Forests of Argentina

Vertical stratification is known in diverse arthropod communities in forests, but little is known about nesting ecology of trap-nesting bees and wasps in Neotropical forests. We studied the vertical colonization of trap-nests by solitary bees and wasps in two forests in Argentina. We obtained 204 nests of seven bee and six wasp species, with 1040 brood cells from which 660 hosts and 32 parasites (21 parasitoid and 11 kleptoparasite) adults emerged from four groups (five species of wasps [Chrysididae, Eulophidae, and Ichneumonidae], four flies [Bombyliidae and Sarcophagidae], three bees [Apidae and Megachilidae], and one species of beetle [Meloidae]). The number of nests, reproductive success, parasitism rate, and mortality did not differ between canopy and understory, nor did the number of brood cells, emerged adults per trap-nest, and total abundance per transect. We found similar assemblages of trap-nesting bees and wasps in both forests, but contrary to our expectations, we did not find any significant difference in the analyzed variables. Our results suggest that access to resources used by trap-nesting bee and wasp females was at least similar, and/or that the microclimatic conditions were homogeneous in canopy and understory. Moreover, our results agree with those reported by some researchers but contrast with others, demonstrating the great variation in the response of bees and wasps nesting in preexisting cavities to vertical stratification in forests and the need for more studies about this topic.