Identification of virulent entomopathogenic nematode isolates from a countrywide survey in India

Abstract

Entomopathogenic nematodes (EPNs) have been successfully used in the USA and Europe for the biological management of insect pests, for example, invasive mole crickets, white grubs and other scarab larvae in lawns and turf, fungus gnats in mushroom, black vine weevil and Diaprepes root weevil in nursery plants and citrus, respectively. The use of EPNs in India is still in the preliminary stages. To find the best EPN isolates for use in local insect pest management programs, we previously collected 35 strains of EPNs from different parts of India, and screened them for insect infectivity at broad temperature range. Here we quantitated the virulence of seven EPN strains showing infectivity at broad temperature range against Galleria mellonella and Spodoptera litura. Three isolates of Steinernema and four isolates of Heterorhabditis were tested. The Heterorhabditis sp. Hmg3 was the most virulent EPN isolate among all the tested nematodes (LC50 = 16.1 infective juveniles (IJs)/insect larvae at 24 h), whereas the isolate Steinernema thermophilum Kr was the most virulent steinernematid (LC50 = 11.8 IJ/insect larvae at 36 h). These strains would be taken up for mass multiplication to facilitate their actual use in insect pest management programs at farmer's fields. Our results suggest that G. mellonella could be used as a primary model for assessing and predicting the virulence of EPN isolates on other insects such as S. litura.