Response of Field Strains of Stored Grain Insect Pest to Phosphine Fumigant

Rhyzopertha dominca, Sitophilus oryzae and Tribolium castaneum collected from grain storage godowns located in different parts of India, were tested for their mortality response at the discriminating phosphine doses following a standardized FAO test method. Less than 20% mortality was recorded for most of the strains in all the three species. LD₉₉ doses for the highly resistant field strains were in the ranges of 5.4 - 10.3, 5.2 - 10.4, 5.0 - 5.9 mg L⁻¹, respectively, for R. dominica in 40 h exposure, and for S. oryzae and T. castaneum in 20 h exposure. For controlling all life stages of the most resistant strains of A dominica and S. oryzae in a 7 d treatment in the presence of wheat grain in desiccators, the required minimum doses were found to be 1200 and 600 ppm, respectively.