Responses of phosphine susceptible and resistant strains of five stored-product insect species to chlorine dioxide

Adults of phosphine susceptible laboratory strains and phosphine resistant field strains of five stored-product insect species were exposed in vials with 0 or 10 g of wheat for different time periods to 0.54 g/m3 (200 ppm) of chlorine dioxide gas. After exposure, adult mortality was determined 5 d later at 28 °C and 65% r.h. The 5-d mortality was 100% in laboratory and field strains of the red flour beetle, Tribolium castaneum (Herbst); sawtoothed grain beetle, Oryzaephilus surinamensis (L.); lesser grain borer, Rhyzopertha dominica (F.); maize weevil, Sitophilus zeamais Motschulsky; and rice weevil, Sitophilus oryzae (L.) that were exposed in vials with 10 g of wheat to chlorine dioxide for 26, 16, 24-34, 18-24, and 15-18 h, respectively. Corresponding exposure durations for these species and strains in vials without wheat were 15, 3, 18-20, 7-15, and 5-7 h, respectively. Dosages of chlorine dioxide producing 99% mortality (LD99) of T. castaneum, O. surinamensis, R. dominica, S. zeamais, and S. oryzae strains in vials with wheat ranged from 14.79−22.57, 8.20-8.41, 15.79-21.60, 10.66-14.53, and 7.67-12.20 g-h/m3, respectively. In vials without wheat, corresponding LD99 values for T. castaneum, R. dominica, and S. zeamais strains were 6.51-8.66, 11.46-23.17, and 5.79-10.26 g-h/m3, respectively. LD99 values for O. surinamensis and S. oryzae could not be computed, because of 100% mortality after a 3-5 h exposure to chlorine dioxide. No adult progeny production of T. castaneum and O. surinamensis was observed after 8 weeks in control and chlorine dioxide-exposed samples. Adult progeny production of Sitophilus spp. was found only in the control samples. The dosage for 99% adult progeny reduction relative to control for R. dominica strains ranged from 10.07 to 18.11 g-h/m3. Chlorine dioxide gas is effective in killing phosphine susceptible and resistant strains of five stored-product insect species and suppressing adult progeny production of three out of the five species.