Virulence and recovery of a cold tolerant Kashmir isolate of EPN, Heterorhabditis bacteriophora (SKUASTK-EPN-Hr 01) with respect to white grub, Heteronychus sp. in Srinagar (J and K)

The virulence of a cold tolerant indigenous Kashmir isolate of Heterorhabditis bacteriophora (SKUASTK-EPN-Hr 01) tested against 1^st, 2^nd and 3^rd instars of white grub, Heteronychus sp. @ 0, 100, 150, 200, 250, 500, 750 and 1000 IJs/grub using Petri dish bioassay method, revealed large differences in the virulence of H. bacteriophora towards the different stages of Heteronychus sp. However, there was a positive correlation between nematode concentration and the insect mortality. The 3^rd instar grubs succumbed to nematode infection later (LT₅₀ = 6.47 days at 250 IJs/grub) than the grubs of 2^nd (LT₅₀ = 3.23 days at 250 IJs/grub) and 1^st instars (LT₅₀ = 2.44 days at 250 IJs/grub). When grubs were in 1^st instar, relatively shorter exposure periods and low nematode concentrations (LC₅₀ = 126.72 IJs/grub at 5 DAE) were needed for achieving lethal nematode infections as compared to 2^nd (LC₅₀ = 176.02 IJs/grub at 5 DAE) and 3^rd (LC₅₀ = 456.35 IJs/grub at 5 DAE) instar grubs where longer exposure periods and high nematode concentrations were required. The recovery of nematode infective juveniles per grub ranged from 47.47-51.32 x 10³, 89.19-92.85 x 10³ and 260.36-263.95 x 10³ IJs in 1^st, 2^nd and 3^rd larval instars of Heteronychus sp., respectively. The total time period between the grub mortality and the initiation of emergence and between grub mortality and the cessation of emergence of nematode infective juveniles from the cadavers ranged from 6-8, 14-16 and 22-24 days, and 21-26, 31-36 and 42-45 days in case of 1^st, 2^nd and 3^rd larval instars of white grub, Heteronychus sp., respectively.