Natural occurrence of entomopathogenic nematode species (Rhabditida: Steinernematidae and Heterorhabditidae) in cotton fields of Tamil Nadu, India

Functional Diversity of Soil Nematodes in Relation to the Impact of Agriculture—A Review

The analysis of the functional diversity of soil nematodes requires detailed knowledge on theoretical aspects of the biodiversity–ecosystem functioning relationship in natural and managed terrestrial ecosystems. Basic approaches applied are reviewed, focusing on the impact and value of soil nematode diversity in crop production and on the most consistent external drivers affecting their stability. The role of nematode trophic guilds in two intensively cultivated crops are examined in more detail, as representative of agriculture from tropical/subtropical (banana) and temperate (apple) climates. The multiple facets of nematode network analysis, for management of multitrophic interactions and restoration purposes, represent complex tasks that require the integration of different interdisciplinary expertise. Understanding the evolutionary basis of nematode diversity at the field level, and its response to current changes, will help to explain the observed community shifts. Integrating approaches based on evolutionary biology, population genetics and ecology can quantify the contribution of nematode fauna to fundamental soil functions. These include carbon transformation, nutrient cycling, pest control and disease transmission. In conclusion, different facets of nematode diversity such as trophic groups, life history traits, variability in body size and/or taxa identities in combination with DNA-based techniques are needed in order to disclose nematode–soil–ecosystem functioning relationships. Further experimental studies are required to define locally adapted and sustainable management practices, through ecosystem-based approaches and nature-based solutions.

Study of Steinernema hermaphroditum (Nematoda, Rhabditida), from the West Uttar Pradesh, India

INTRODUCTION

The entomopathogenic nematodes have been reported from all continents (except Antarctica) and almost all regions of the world. Surveys of EPNs in India has resulted in the recovery of several isolates of Steinernema. Among one of them, isolate CS34 was identified as S. hermaphroditum Stock, Griffin & Chaerani, 2004. We investigated the identification and the pathogenicity of S. hermaphroditum in District Meerut of Western Uttar Pradesh, India.

MATERIALS AND METHODS

The Steinernema was examined for its pathogenicity and accurate identification by the mean of morphological and molecular technique and its geographical distribution was mapped based on meta-analysis of the ITS GenBank records.

RESULTS

The surveys of agricultural soils of district Meerut, India, resulted in the isolation of one strain from entomopathogenic nematode labelled CS34 through Galleria baiting technique. Morphological characters and morphometrical analysis indicated that the strain CS34 was closely related to the "glaseri" group of Steinernema spp. The Nblast results indicated that ITS rDNA sequence had no nucleotide differences in comparison with the S. hermaphroditum (JQ687355). However, one variation in the D2-D3 segment of 28S rDNA was observed in comparison with the AY598358. The phylogenetic analysis using ITS and 28S rDNA indicated that the Indian S. hermaphroditum could be placed together with other S. hermaphroditum, with strong posterior probability. Besides, the PCA analysis demonstrated some variability within the test populations. The distribution of S. hermaphroditum based on meta-analysis of the GenBank records showed its presence in the three Asian countries-India, Thailand and Indonesia. The Indian strain of S. hermaphroditum also tested positively for its virulence against three major pests, namely, Galleria mellonella, Helicoverpa armigera, and Spodoptera litura, with resultant which showed good efficacy on the mortalities.

CONCLUSIONS

In conclusion, the economy of India is agriculture-based, but there are huge losses due to different insect pests infesting different crops. Steinernema hermaphroditum CS34 is an indigenous species to Indian subcontinent and efforts should be made to evaluate its virulence and pathogenicity against the other agricultural pests hampering productivity throughout the country. This may lead to incorporate S. hermaphroditum strain CS34 as a regular biological control agent against important lepidopteran pest in integrated pest management programs in the future.

Biodiversity of entomopathogenic nematodes in Italy

An investigation was carried out on the distribution and biodiversity of steinernematid and heterorhabdtid entomopathogenic nematodes (EPN) in nine regions of Italy in the period 1990–2010. More than 2000 samples were collected from 580 localities and 133 of them yielded EPN specimens. A mapping of EPN distribution in Italy showed 133 indigenous EPN strains belonging to 12 species: 43 isolates of Heterorhabditis bacteriophora, 1 of H. downesi, 1 of H. megidis, 51 of Steinernema feltiae, 12 of S. affine, 4 of S. kraussei, 8 of S. apuliae, 5 of S. ichnusae, 3 of S. carpocapsae, 1 of S. vulcanicum, 3 of Steinernema ‘isolate S.sp.MY7’ of ‘S. intermedium group’ and 1 of S.arenarium. Steinernematids are more widespread than heterorhabditids and S. feltiae and H. bacteriophora are the most commonly encountered species. Sampling sites were grouped into 11 habitats: uncultivated land, orchard, field, sea coast, pinewood, broadleaf wood, grasslands, river and lake borders, caves, salt pan and moist zones; the soil texture of each site was defined and the preferences of habitat and soil texture of each species was assessed. Except for the two dominant species, S. feltiae and H. bacteriophora, EPN occurrence tends to be correlated with a specific vegetation habitat. Steinernema kraussei, H. downesi and H. megidis were collected only in Sicily and three of the species recently described – S. apuliae, S. ichnusae and S. vulcanicum – are known only from Italy and seem to be endemic.