Oscheius myriophila (Nematoda: Rhabditida) isolated in sugar cane soils in Mexico with potential to be used as entomopathogenic nematode

The endosymbiont and the second bacterial circle of entomopathogenic nematodes

Single host-symbiont interactions should be reconsidered from the perspective of the pathobiome. We revisit here the interactions between entomopathogenic nematodes (EPNs) and their microbiota. We first describe the discovery of these EPNs and their bacterial endosymbionts. We also consider EPN-like nematodes and their putative symbionts. Recent high-throughput sequencing studies have shown that EPNs and EPN-like nematodes are also associated with other bacterial communities, referred to here as the second bacterial circle of EPNs. Current findings suggest that some members of this second bacterial circle contribute to the pathogenic success of nematodes. We suggest that the endosymbiont and the second bacterial circle delimit an EPN pathobiome.

Description of Oscheius cyrus n. sp. (Nematoda: Rhabditidae) as new entomopathogenic nematode from Iran

A new species of the genus Oscheius, Oscheius cyrus n. sp., collected in the moist soils taken from forest heights in the north of Iran, is recorded. A comprehensive description, comprising molecular (internal transcribed spacer (ITS), 18S, and 28S rDNA genes) information, morphometrics data, light microscope and scanning electron microscope images, is supplied. The species resembles Oscheius myriophilus. However, the highest ranges for female body length, female tail, infective juvenile tail length, median bulb, absence of epiptygma and lateral field incisures number vary. The new species was distinguished from Oscheius insectivorus by the general lip region. The male was not found. Molecular analysis showed that the new species has the most similarity to O. myriophilus both in the ITS and 18S regions. Morphological and molecular data confirmed its belonging to the Insectivora-group. Furthermore, the species of Ochrobactrum pseudogrignonense was reported as a dominant associated bacterium of the new Oscheius species. Finally, the mortality of the host after seven days varied from 20% to 82.5%, depending on nematodes' concentration.

Evaluation of indigenous entomopathogenic nematodes in Southwest China as potential biocontrol agents against Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura is a notorious leaf feeding insect pest in the Asia-Pacific region and leads to a significant economic loss in vegetable and field crop production. Entomopathogenic nematodes (EPNs), lethal parasites of insects, are used as biocontrol agents. Yunnan Province in China is a well-known region due to its rich biodiversity. In the present study, a survey of EPNs using the Galleria-baiting technique was conducted in 2017 and 2018 throughout the entire Yunnan province. In total, 789 soil samples were collected from 232 sites, of which 75 samples were positive for EPNs. Phylogenetic analyses of ITS, D2D3 expansion region of the 28S rRNA gene, as well as mitochondrial cytochrome c oxidase subunit I (COI), were performed to identify isolated nematode species and evaluate their genetic diversity. In total, 13, 3, and 58 identified populations belong to Steinernema, Heterorhabditis, and Oscheius, respectively. The phylogenetic relationships of EPN species in the three genera were analyzed with the Neighbor-Joining method. The virulence of the trapped isolates in the genera of Steinernema, Heterorhabditis, and Oscheius against S. litura was evaluated. Ten new indigenous isolates from Steinernema and Heterorhabditis showed prominent virulence to S. litura within 48 hr which is equivalent to that of commercial EPNs populations. The present study provides background information on indigenous EPN resources for S. litura control in Asia-Pacific region.

First record of Oscheius myriophilus () (Rhabditida: Rhabditidae) from Iran; and its efficacy against two economic forest trees pests, Cydalima perspectalis (Walker, 1859) (Lepidoptera: Crambidae) and Hyphantria cunea () (Lepidoptera: Erebidae) in laboratory condition

The box tree moth (BTM), Cydalima perspectalis and the fall webworm (FWW), Hyphantria cunea are two invasive pests of forest trees that have been recorded from Hyracinan forests in north Iran for the first time in 2016 and 2002, respectively. In a search for tentative native entomopathogenic nematode species (EPNs) with potential biocontrol ability against lepidopteran pests of forest trees in north Iran, Oscheius myriophilus was isolated by soil-baiting method from forests of Amlash in the east of Gilan province. The Iranian isolate of this species is characterized by 870-1,247 μm long hermaphrodites having 17-20 μm long stoma, vulva at 45.5-53.1% of body length, tail 90-126 μm long, common males with 38-49 μm long spicules and 583-791 μm long dauer larvae. Compared to the type and other populations, no remarkable differences were observed for this population. The phylogenetic affinities of this isolate with other rhabditid nematodes were studied using partial sequences of small, and the D2-D3 expansion segments of the large subunit ribosomal DNA (SSU and D2-D3 LSU rDNA). This is the first record of the species from Iran. The pathogenicity of Iranian isolate of O. myriophilus was evaluated on the larvae of two important aforementioned forest trees pests, BTM and FWW under laboratory conditions. The results indicated that the suspension of 500 infective juveniles per ml (IJs/ml) of the nematode was the most effective treatment on fifth instar larvae of BTM and FWW, causing 100 and 95% mortality after 48 h, respectively. The lethal concentration 50 (LC50) values of the nematode were 74.5, 152.7, 99.9, and 197.3 IJs/ml on fifth and fourth instar larvae of BTM, and fifth and fourth instar larvae of FWW, respectively, after 48 h at 25°C and 60% relative humidity. Together, present results corroborated the efficacy of the Iranian isolate of Oscheius myriophilus for biocontrolling of BTM and FWW in laboratory conditions.