Efficacy of ozone against Rhyzopertha dominica adults in wheat

Adults of a laboratory strain of the lesser grain borer, Rhyzopertha dominica (F.), were exposed to ozone concentrations of 0.42 and 0.84 g/m3 for up to 36 and 30 h, respectively, to estimate lethal time (LT) and lethal dose (LD) to kill 99% of insects at 28 °C and 65% r.h. After exposure, adult mortality was counted daily for 5 d. Adult progeny production data from ozone-exposed adults was used to estimate effective time (ET) and effective dose (ED) for 99% reduction in adult progeny production. At 0.42 and 0.84 g/m3, LT99 values for adult mortality on day 1 were 67 and 42 h, respectively. Corresponding LD99 values for adult mortality on day 1 were 28 and 36 g-h/m3, respectively. On day 5, LT99 and LD99 values decreased by 52–54% of day 1 values. The LT99 or LD99 values over days 1 through 5 decreased in a nonlinear fashion, suggesting delayed toxic effects of ozone. The ET99 value for reduction in adult progeny production was 22 h at an ozone concentration of 0.84 g/m3, whereas it was 39 h at 0.42 g/m3. Like LD99 values, ED99 value for adult progeny reduction at 0.42 g/m3 of ozone was lower than at an ozone concentration of 0.84 g/m3. Doubling the ozone concentration from 0.42 to 0.84 g/m3 did not reduce the LT99 or ET99 values by 50%. In general, the LD99 values on days 1 through 5 at an ozone concentration of 0.84 g/m3 were significantly greater than similar values at an ozone concentration of 0.42 g/m3, suggesting that R. dominica adults tend to be more susceptible when exposed to a low ozone concentration for extended time periods.