Efficacy of ozone gas against laboratory and field strains of four stored-product insect species

The efficacy of ozone, as an alternative fumigant to phosphine, was tested against four economically important stored-product insect species at 27.2°C and 20.4% r.h. Adults of phosphine susceptible laboratory strains and phosphine resistant field strains of the red flour beetle, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.), were exposed to an ozone concentration of 0.42 g/m3 (200 ppm) for 1, 2, 3, 5, 6, 8 and 10 h in the presence (10 g) or absence (0 g) of wheat (Triticum sp.). Mortality after the ozone exposure was assessed 5 days later. Complete mortality of Sitophilus spp. required a 3 to 4 h exposure to ozone, whereas that of O. surinamensis required 6 to 10 h. Adults of T. castaneum were the least susceptible to ozone, and after a 10 h exposure, the highest mortality recorded was 82 to 95%. The LT50 and LT99 values were estimated by probit analysis based on 5 d corrected mortality data. The LT99 values for Sitophilus spp., O. surinamensis, and T. castaneum were 2.00 to 5.56, 4.33 to 11.18, and 14.35 to 29.89 h respectively.