Natural occurrence and bioefficacy of Himalayan strains of Heterorhabditis spp. nematodes against major lepidopteran insects

Survey for entomopathogenic nematodes (EPNs) was conducted in ten districts of Himachal Pradesh (North West Himalayas) India, during 2011-13.  In all, 930 soil samples from 131 locations were analyzed for the occurrence of the nematodes.  The frequency of occurrence of these nematodes was very low (3.82%). The entomopathogenic nematodes were recovered from fruit orchards only having lighter soils.  The nematodes from all the locations were identified as Heterorhabditis. Nematode cultures from different locations were considered as isolates and were designated as Heterorhabditis spp. (HSG), Heterorhabditis spp. (HKM) and H. bacteriophora (HRJ). These isolates, along with one commercial isolate i.e. H. indica (procured from NBAII, Bengaluru, India) were evaluated for their pathogenic effects against Spodoptera litura, Helicoverpa armigera, Plutella xylostella and Agrotis segetum in Petri plates/soil/screen house.  All these three local isolates including the commercial isolate proved pathogenic variably to different insect-pests. In screen house testing on cabbage, H. bacteriophora (HRJ) was found highly effective against S. litura, H. armigera and P. xylostella. The virulence of these isolates was considered of the medium level.  Besides, host invasion studies in Achroia  grisella revealed maximum penetration through natural openings, other than mouth. For in vivo mass production of local EPNs, Corcyra cephalonica, A. grisella and Bombyx mori were used.  The average yield of IJs/larva was minimum (23020-26030) in C. cephalonica and maximum in B. mori (463080-546840) for different EPNs.  For in vitro mass production, chicken offal medium was used.  The yield was maximum for H. bacteriophora (HRJ) (17.70 x 10⁶ IJs/flask).