Mortality time of immature stages of susceptible and resistant strains of <i>Sitophilus oryzae</i> (L.) exposed to different phosphine concentrations

Abstract

The mortality time on egg, larvae and pupae of four strains with resistance factor 1, 69, 160 and 295 to phosphine of Sitophilus oryzae (L.), which were expressed in R₁, R₆₉, R₁₆₀ and R₂₉₅ in this report, respectively, were investigated with stable concentrations of 100, 300, 500, 700 and 900 mL m^-3 of phosphine in a well sealed fumigation chamber. The mortality time on all immature stages was about 10 d for strain R₁, more than 15 d for all resistance strains exposed to 100 mL m^-3 of phosphine. Mortality time on egg and larvae of R₁ was 9 and 6 d at 300 and 700 mL m^-3, respectively. But it was only 4 d and 2 d for pupae of R₁ at 700 and 900 mL m^-3, respectively. The mortality time on immature stages of R₆₉ was 12 and 5 d with the 300 and 700 mL m^-3, respectively. And that on immature stages of strain R₁₆₀ and R₂₉₅ was 15 and 10 d with phosphine of 300-700 mL m^-3, respectively. With the fumigant of 900 mL m^-3, the full death time were 5 d for larval of all strains, 5d for pupae and egg of R₁ and more that 8 or 9 d for pupae and egg of three resistance strains. The egg and pupae of S. oryzae were the most tolerant stages to phosphine both for susceptible and resistance strains.

Keywords: Sitophilius oryzae, Immature stage, Phosphine, Mortality time