The oligolecty status of a specialist bee of South American Prosopis (Fabaceae) supported by pollen analysis and floral visitation methods

Despite the nest pollen provisions in Western Argentina are composed only of Prosopis, the fact that the ground-nesting bee Eremapis parvula visits several floral hosts suggested that it is a generalist bee species. In the South American Dry Chaco forest, seven nest aggregations of E. parvula were found during three different spring periods. From 34 to 73 species of floral hosts were recorded around each nest aggregation. However, all nest pollen samples were composed of Prosopis pollen alone, as previously found in nests from Western Argentina. Thus, pollen analysis proved that E. parvula is a specialist bee of Prosopis. The “monolecty” and “narrow oligolecty” pollen specialization categories cannot be differentiated using pollen analysis alone. For this reason, a complementary floral visitation method was used. As several Prosopis species have been reported in floral records, the narrow oligolecty category for E. parvula is supported here. Considering that this exomalopsine is a multivoltine bee, and that flowers of some of the more than seven Prosopis species are always available during spring, synchronization between them in rainy periods is highly probable. Thus, it is unlikely that E. parvula has to forage on alternative pollen hosts.