Plants, aphids and parasitoids: trophic interactions in agroecosystems in the province of Santa Fe, Argentina and a key to the identification of Aphidiinae and Aphelinidae (Hymenoptera) known to the region

Parasitoids (Hymenoptera: Aphidiinae; Aphelinidae) exert a significant pressure regulation in pest aphid populations (Hemiptera: Aphididae). In order to contribute to the biological control of aphids, the objective of this study was to identify plant-aphid-parasitoid trophic interactions occurring in crop fields and their vegetated borders and to provide an identification key for parasitoids recorded in the province of Santa Fe (Aphidiidae and Aphelinidae). Over four years, (2009-2013), 10 transects of 0.5 m in crops (alfalfa, oats, wheat and canola) and non-crop edges were randomly selected in 28 fields from six districts of the province. Samples of each observed species were taken and mummies (parasitized aphids) were reared in the laboratory, until adult emergence, for identification. Regional matrix for plantaphid-parasitoid interaction registered in crops and non-crop and useful aspects for aphid pest control are discussed. Known host ranges for eleven species of paresitoids were expanded and an illustrated key based on female morphology of both groups of parasitoids, and another based on mummies morphology and other evidences of parasitoids emergence from their hosts, were provided.