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.
Phosphine, stored grain insects, resistance, mortality response
