Heterorhabditis sonorensis n. sp. (Nematoda: Heterorhabditidae), a natural pathogen of the seasonal cicada Diceroprocta ornea (Walker) (Homoptera: Cicadidae) in the Sonoran desert.

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-anal 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: 105mum) 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.

Ecological characterization of Heterorhabditis sonorensis (Caborca strain) (Nematoda: Heterorhabditidae), an entomopathogenic nematode from the Sonoran Desert.

Heterorhabditis nematodes are parasites of a wide range of soil-dwelling insect species. Although these nematodes have been exploited as biological control agents since the last half of the 20th century, much research remains to be done to understand how these organisms function in agricultural and other ecosystems. In this study, we present some ecological traits of Heterorhabditis sonorensis, a natural parasite of the cicada Diceroprocta ornea, from the Sonoran Desert. Specifically, we evaluated its infectivity across a diverse panel of insect groups and assessed its fitness (infectivity and reproduction) considering different temperatures, and soil moisture levels. Three other Heterorhabditis species served as points of comparison for temperature and soil moisture assays. Host range experiments indicate that H. sonorensis, although isolated from seasonal cicada nymphs, is more virulent and reproductively fit in the lepidopteran hosts tested. This nematode has an optimum temperature range at 25-30 °C but can also successfully reproduce at temperatures ranging from 15 to 35 °C. Additionally, this nematode is adapted to a variety of soil moisture conditions with successful infections across the tested moisture range (3%-20%). Finally, we demonstrate that H. sonorensis infective juveniles have a high survival rate (over 80%) at various storage temperatures (10-25 °C) after 24 weeks of storage and remain infective as revealed by the post-storage infection assays.