Effect of Ultra-Violet Radiation Protectants on Indigenous Isolates of Entomopathogenic Nematodes

The inability of most EPN isolates to withstand UV rays in solar radiation is one of the major impediments for their use against foliar insect pests. To overcome this, four chemicals viz., PABA (para amino benzoic acid), Congo red, zinc oxide and titanium dioxide were tested at four concentrations (0.5, 0.25, 0.1 and 0.05%) to identify a suitable UV protectant and to standardize its concentration for use of indigenous isolates of Heterorhabditis bacteriophora and two isolates (Janti and RB-5) of Steinernema species. Nematode suspensions (1000 IJs/ml) treated with the above chemicals at different concentrations were exposed to UV radiation in a laminar flow bench for 30 and 60 min. PABA and Congo red provided nearly absolute protection from UV radiation in all the three EPN isolates. Zinc oxide was not effective (70-90% mortality in exposed IJs). Titanium dioxide protected H. bacteriophora completely at 0.5% concentration only, whereas in Steinernema Janti isolate protection was only 76% and in RB-5 isolate 40% IJs were alive even at 0.5% cone. The IJs exposed to PABA and Congo red remained infective to Galleria mellonella larvae whereas titanium dioxide hampered the infectivity. PABA and Congo red at 0.25%, and zinc oxide and titanium dioxide at 1% were not phytotoxic to mungbean. The effect of UV protectants was not nematode density-dependent, since they were equally effective at nematode populations of 1000, 2000 or 4000 IJs per ml.