Abstract
The large genus Calliopsis (Andrenidae, Panurginae) is composed of ten subgenera with polylectic and presumably oligolectic species. These categories have been mainly developed from floral visits of female bees collecting pollen. In the present study, pollen analyses of nest provisions and scopal loads from museum specimens of the monotypic subgenus Ceroliopoeum were carried out to assess its degree of specialization to pollen host-plants. Despite the great variability of floral resources close to two active nest aggregations in the Chaco sites (83 and 44 melittophilous taxa from 36 and 17 families, respectively), the only host-plant recorded in all nest pollen samples was Prosopis. This genus was represented by six species and their hybrids, all having similar pollen morphology. The nesting sites in Monte scrub also contained several Prosopis species, some of which had different pollen morphology from those of the Chaco forest. Two different Prosopis pollen types were identified in all samples. Since the whole geographic distribution of C. laeta matches with the range of Prosopis, its strong association with this pollen host seems to be well supported. However, the low number of study populations (four) could erroneously indicate oligolectism. A broader sampling is necessary to ensure the character of specialization. Most Calliopsis species have been identified as oligolectic. Yet, this categorization has mainly been based on floral visits and a large diversity of floral hosts has been recorded for each bee species. Further analyses are necessary to confirm the relationship of this genus with its pollen hosts. Moreover, as most of them have short to medium phenologies (up to 4 months) their presumably oligolecty can be due to a local specialization (i.e. variable according to location) typical of polylecty.
Highlights
The legume family (Fabaceae sensu lato or Leguminosae) is a mainly bee-pollinated plant group that constitutes a major food source for the entire taxonomic spectrum of bees (Arroyo 1981)
Floral visits were recorded on P. ruscifolia and P. alba during a whole day (22nd September 2011), but Calliopsis laeta was only observed on Prosopis alba
Prosopis pollen was found in nest samples in spite of the presence of abundant alternative pollen hosts being available, such as Melilotus, Capparis, Cercidium, Albizia and others (Appendix II)
Summary
The legume family (Fabaceae sensu lato or Leguminosae) is a mainly bee-pollinated plant group that constitutes a major food source for the entire taxonomic spectrum of bees (Arroyo 1981). The South American Chaco is a forest characterized by the abundance of woody and herbaceous Fabaceae, mainly the woody mimosoids Prosopis and Acacia, Zygophyllaceae, Anacardiaceae, Celastraceae, Rhamnaceae, Capparidaceae, Santalaceae, Ulmaceae s.l., Cactaceae and Bromeliaceae (Cabrera & Willink 1973). Prosopis is a species-rich plant genus and most species are quite uniform in floral and inflorescence phenotypes (Burkart 1937; Palacios & Bravo 1981). Prosopis contains 45 species and is mainly distributed in arid and semi-arid regions of the world (Burkart 1976; Palacios & Brizuela 2005). Recent studies showed that it is not a natural group, and that Old world species are not true
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