Abstract Caenorhabditis elegans is a free-living nematode, belonging to the bacterivorous trophic group. Although it was cited in several countries, in different types of ecosystems and in associations with other organisms, the wild habitats of this nematode have not yet been precisely defined. In Argentina, C. elegans was recently isolated from the hoverfly Allograpta exotica, a voracious predator with potential biological control against aphids in horticultural crops. In this frame, the objectives of this study were (i) to characterize it molecularly and morphologically (ii) to report a wild strain of C. elegans for the first time from Argentina, (iii) to present a new ecological niche by associating it with A. exotica and (iv) to evaluate the pathogenicity against these insects. The results of the morphological and molecular analyses made it possible to determine that the isolated nematode was C. elegans, thus establishing the ARGLP1900 wild strain as the first record of this nematode for Argentina. A new association was described, since there are no records of interaction between C. elegans and A. exotica, providing information on a new ecological niche. The new wild strain found in this work, could be appropriate for comparative genomic studies with other C. elegans strains.

Abstract: Oxyurid nematodes parasitizing the mole cricket Neoscapteriscus vicinus were isolated in the framework of sampling fields of mole-crickets from the pampean region, in Argentina. In this work, molecular characterization of the 18S rRNA partial sequence of nematodes belonging to the families Thelastomatidae (Cameronia arecoensis Marchissio and Miralles 1987) and Travassosinematidae (Binema korsakowi Sergiev 1923 and Binema klossae, Marchissio and Miralles 1993) were carried out. This is the first world report of sequences belonging to B. klossae and C. arecoensis and first Argentinian report of B. korsakowi sequence. Also, morphological and morphometric features of B. klossae, B. korsakowi and C. arecoensis from Argentinian populations are reported.