Virulence of Native EPN Strains and their Symbionts alone to Polyphagous Lepidopteran Pests vis a vis Model Insect Galleria melonella along with in vivo Production

Abstract

Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae are obligate parasites of insects and can control pests due to the symbiotic bacteria that kill the insect host by septicemia and make the environment favourable for EPNs development and reproduction. In the present paper the virulence of three Heterorhabditis sp. strains and their respective symbiotic bacteria strains alone (Photorhabdus luminescens strains) was tested under laboratory conditions against larval stages of model insect host Galleria mellonella along with two important polyphagous pests viz., Helicoverpa armigera and Spodoptera litura. The results revealed that the virulence of the three strains of Heterorhabditis sp. tested, varied considerably in terms of both LC 50 as well as LT 50. Feeding assays of symbiotic bacteria Photorhabdus luminescens showed that strain SG-Ngp was most effective against S. litura (LC 50 = 4.06 x 10 5 cells/gm). It is worth mentioning that all the three strains showed lower LC 50 against S. litura compared to H. armigera which concurrent with the results of IJ experiments. Among the three strains, Hms1 was found to be most efficient IJ producer, via both G. mellonella and H. armigera. Although, when H. armigera was used as the host for this strain, the yield increased by 16%. Thus, this study provides an important insight on the native EPN strains with possible insecticide potential. Besides our studies suggest that not only EPN but also its associated symbiotic bacteria alone can be used for effective pest control.