Nesting ecology of the bee Hylaeus (Hylaeopsis) platensis n. sp. (Colletidae, Hylaeinae) with description of its parasite, Grotea hylaeivora n. sp. (Ichneumonidae, Labeninae)

Nests of the new species Hylaeus platensis were found in mature inflorescence scapes of the native tussock grass Cortaderia selloana, in Entre Ríos, Argentina. The nests occupied the hollow stems. Detailed information on the structure of the nests is presented. Nests had up to 12 linearly arranged cells of translucent cellophane-like lining with various bee stages, with semi-liquid pollen-nectar provisions, or empty with a dry fecal plate at the base. Accumulations of sawdust and empty spaces were also sometimes found. Pollen hosts were studied by palynological analysis of provisions and feces from the nests. To characterize the diet, pollen counts, pollen volumes, and the index of relative importance (IRI) were taken into account. The results show that H. platensis is a polylectic bee, since it collects pollen from genera in at least four different plant families. A predominance of Salix humboldtiana pollen in most samples is interpreted as the result of occasional preference. A parasitoid ichneumonid, Grotea hylaeivora n. sp., was reared from the nests. Large larvae of this parasitoid wasp were found occupying the length of two neighboring Hylaeus cells, within a membranous cocoon separated by disc partitions. A sum of plesiomorphic characteristics present in this species suggest that G. hylaeivora may represent the sister taxon to all extant species of Grotea. Both the bee and the ichneumonid new taxa are described and illustrated.