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Four bionomical features are here described for the seven stingless bees that inhabit a new meliponine beekeeping area: the Argentinean Chaco region. The most commonly visited plants were of herbaceous habits, predominantly had flowers of white/creamy to yellowish colour, with small-sized flowers and were of moderate mass-flowering degree. Lestrimelitta chacoana was the only robber species. The most commonly found nesting substrate was large living tree trunks, and most nests were found at the base of the trunks. Sometimes, nesting substrates and floral resources were provided by the same woody plant. Cryptic small-to medium-sized cerumen tube-like unornamented nest entrances were the most commonly found. Nest defence included aggressive (Scaptotrigona jujuyensis) and docile behaviour; the latter was classified into timid and non-timid. A key to identify the Meliponini fauna of this region is provided. The regional pattern of bionomical features seems to be associated with subtropical climate conditions. The majority of these bee species are suitable for Meliponiculture in the Chaco region.aggressive bee / dead tree trunk / docile bee / living tree trunk / subtropical Meliponini bees

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The pollen preferences of three Meliponini species (Geotrigona argentina, Scaptotrigona jujuyensis and Tetragonisca fiebrigi) were studied in the Chaco forest of South America. Surprisingly, a large number of pollen types with small volumes and size were found in pollen masses stored in the 18 nests studied. Small pollen grains are commonly found in small flowers with short pistils, a flower morphology adapted to the pollination by these small-to medium-sized bees. The prevalence of grains with small volumes may be due to the preference of Meliponini bees for small flowers with short pistils, supporting a previously suggested hypothesis of diffuse co-evolution between mass-flowering trees and these tiny bees in Neotropical habitats. However, the opportunistic foraging habit of these generalist bees would suggest that the large number of grains with small size is due to their greater availability in the Chaco forest nearby the nests. This study also provides measurements and descriptions of pollen cytoplasmic shapes as well as a new classification of pollen volumes based from measurements of the five pollen size categories using non-acetolyzed grains.