Tropical forests are known for their diverse insect fauna. We aimed to determine the effect and relative importance of latitude, elevation and climatic factors affecting species richness and turnover in euglossine bee assemblages along a gradient of 18° latitude from tropical rainforests to subtropical, deciduous dry forests in Peru and Bolivia. Sixteen forest sites were sampled during the dry season. Variance partitioning techniques were applied to assess the relative effects of the spatial and environmental variables on species richness and composition. Furthermore, we conducted a Species Indicator Analysis to find characteristic species for the biogeographic zones. There was a significant decrease in species richness towards the subtropical area. The best predictors of species richness were precipitation and its consequences on soil properties as well as temperature seasonality. The abundance of euglossines was most closely related to precipitation and soil-pH, but the causal links of abundance to these factors is unclear since soil-pH itself is correlated to a drastic turnover of vegetation structure. Based on the analysis of assemblage composition we propose three different assemblages with a transitional zone at the southern tropical area. The biogeographical distribution of euglossine bees along our study transect appears to be primarily related to climatic conditions and does not reflect the common subdividion of Amazonia into drainage systems.