Susceptibility of Stored-Product Insect Pessts (Indian Meal Moth. Plodia interpunctella [Lepidoptera: Pyralidae]; Granary Weevil, Sitophilus granarius; and Maize Weevil,S. zeamais [Coleoptera: Dryophthoridae]) to Propylene Oxide Fumigation at Normal Atmospheric Pressure

摘要

Propylene oxide (PPO) fumigation at dosages of 12, 24, and 36 mg/1 for 24 or 48 hours at 10°C under normal atmospheric pressure (NAP) was carried out using PPO/N_2 gas mixture to investigate susceptibilities of the egg, larva (including diapause larvae of Plodia interpunctella), pupa, and adult stages of P. interpunctella and Sitophilus granarius and the pupal stage of S. zeamais. All stages tested were buried in wheat grains stored in an acrylic fumigation box with 0.1kg/1 loading factor to simulate commercial silo fumigation and were fumigated. Complete mortalities were attained for eggs, nondiapause larvae and adults of P. interpunctella at the condition of PPO 24 mg/1 for 48 hours. The pupal stage, however, could not be killed completely at even PPO 36 mg/1 for 48 hours. Diapause larvae with a diapausing period of at least one month were barely killed and showed only 2.7% mortality at PPO 36 mg/1 for 24 hours. Complete mortality for each stage of S. granarius was not achieved in any fumigationcondition tested. It was revealed that all stages of S. granarius have less susceptibility to PPO fumigation compared to stages of P. interpunctella. Pupae of S. zeamais were relatively more susceptible to PPO than those of S. granarius due to higher mortalities obtained. Because higher sorption of PPO to wheat grains was observed during fumigation, PPO/N_2 fumigation at NAP was not suitable for silo fumigation of grains that is usually executed with a higher loading factor, more than 0.3 kg/1 at quarantine treatment PPO/C0_2 gas mixture fumigation could radically raise mortalities, up to 99% for diapause larvae of P. interpunctella and pupae of S. granarius, than that of fumigation with PPO/N_2 gas. Adopting gas mixture fumigation with other fumigants such as C0_2 or vacuum fumigation were considered more effective in order to ensure both PPO toxicity and safe use.