Summary Background and aims: To detect floral interactions between species of family Amaryllidaceae and bees (Hymenoptera: Apoidea: Anthophila), the presence of pollen from wild and cultivated Amaryllidaceae in the nests of wild non-Ap/s bees collected in three Argentine eco-regions (Pampa, Pampa-Espinal and Chaco) was investigated. M&M: A total of 500 microscopic slides of pollen and honey from 369 nests of 25 bee species were analyzed. The identification was made by comparing the pollen from nests with the reference pollen obtained from the flowers collected in the studied areas. The flower phenology of the wild species and floral visitation with catching of bee individuals were also recorded. Results: A total of six pollen types belonging to Amaryllidaceae were identified in the pollen diet of only five of the 25 bee species analyzed. Among wild Amaryllidaceae, two different flowering patterns were observed: 1) in the wet periods of winter-spring and/or summer-autumn, and 2) very synchronous and ephemeral, triggered by the rains in summer-autumn. Conclusions: The five bee species presenting Amaryllidaceae pollen in their nests and most bees collected on flowers were polylectic (generalized pollen usage) from Apidae and Halictidae families. More research is needed to deeply study the floral associations between bees and Amaryllidaceae in Argentina, and it is expected that there will be a higher number of bee species with pollen specialization (oligolecty) towards particular clades of this lineage of monocots.

Resumen Introducción y objetivos: A fin de detectar patrones de asociaciones entre Amaryllidaceae y abejas (Hymenoptera: Apoidea: Anthophila), se investigó la presencia de polen de Amaryllidaceae silvestres y cultivadas en nidos de abejas silvestres no Ap/s colectados en tres ecorregiones de Argentina (Pampa, Pampa-Espinal y Chaco). M&M: Se analizaron un total de 500 preparados microscópicos de polen y miel de 369 nidos de 25 especies. La identificación fue realizada por comparación con polen de referencia de flores recolectadas en los sitios estudiados. También se registraron la fenología floral de las especies silvestres y visitas florales con captura de individuos de abejas. Resultados: Se identificaron seis tipos polínicos de Amaryllidaceae en la dieta polínica de sólo cinco de 25 especies de abejas. Entre las Amaryllidaceae silvestres se observaron dos patrones de floración marcadamente diferentes: 1) en épocas húmedas invierno-primaverales y/o estivo-otoñales, y 2) sincronizadas y efímeras, desencadenadas por las lluvias estivo-otoñales. Conclusiones: Las cinco especies de abejas con polen de Amaryllidaceae en sus nidos y la gran mayoría de las recolectadas en las flores fueron polilécticas (uso de polen generalizado) de las familias Apidae y Halictidae. Existe mucho por investigar en cuanto a las asociaciones florales entre abejas y Amaryllidaceae en Argentina, y se espera que hayan más especies de abejas con especialización por polen (oligolectia) hacia clados particulares de este linaje de monocotiledóneas.

Abstract: An entomopalynological study to assess pollen use by wild bees was performed in an urban environment with riparian native forest in the Chaco region of Argentina. A combined method for sampling pollen loads and garbage pellets at nest entrances in four stingless bees with different entrance size and forager traffic was here successfully used. Sampling was carried out in a short period of time (late winter) and located within a distance of 50 m. Pollen analysis using acetolysis showed that most identified pollen types (31) were from native species, 12 from ornamental exotic species, 5 included native and ornamental exotic species and 18 of uncertain status. A much broader pollen spectrum was present in garbage pellets (62 types) than loads (14 types). A few resources from previous blooming (late spring-summer) were identified in garbage pellets, which were mainly composed of current flowerings. From the 66 pollen types found in all samples, many (18) remained unidentified due to the complex nature of the vegetation surrounding the nests and the generalist behaviour of these bees. The versatile foraging behaviour on spontaneous (mostly native) and cultivated (mostly ornamental exotic) pollen resources is an important issue for the conservation and rearing of stingless bee colonies in urban habitats where native flora is preserved, particularly the riparians, where a high richness of blooming plants is available.