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A new Heterorhabditis species was isolated from nymphal stages of the seasonal cicada Diceroprocta ornea (Walker) in an asparagus field in the state of Sonora, Mexico, Concomitantly, another isolate of the same nematode species was also collected from an oak woodland habitat in the Chiricahua Mountain range in Southeastern Arizona. Morphological and molecular Studies together with cross-hybridization tests indicate these two isolates are conspecific and represent a new undescribed Heterorhabditis sp. This new species is distinguished from other species in this genus by a combination of several qualitative and quantitative morphological traits. Key diagnostic features include: presence of a pronounced post-arial swelling in the hermaphrodite; male with nine pairs of bursal rays, with pairs 4 and 7 bent Outwards and one pair of papillae placed on the cloacal opening, value of D% (average: 79): infective juveniles With a well developed cuticular tooth. long tail (average: 105 mu m) and Values of D% (average: 90) and E% (average: 99). in addition to these diagnostic characters, cross-hybridization tests between the new species with H. bacteriophora and H. mexicana yielded no fertile progeny. Comparison of ITS rDNA sequences with other available sequences of described species depicted the two isolates as a new species. Phylogenetic analysis of these sequence data placed H. sonorensis n. sp. as a member of the indica-group. (C) 2008 Elsevier Inc. All rights reserved.