Acute and delayed toxicity effects of ozone on internal and external feeders of stored products

Abstract: With the ban of methyl bromide, and the many problems associated with the use of other conventional control methods, the search for potential alternatives for the control of stored product insect pests has been ongoing. Ozone, a highly oxidizing gas, is one of such potential alternatives being studied for its use in the management of insect pests on stored products. In this study, we investigated the efficacy of ozone for controlling adults of Oryzaephilus mercator (Fauvel) (Coleoptera: Silvanidae), Lasioderma serricorne (Fabricius) (Coleoptera: Anobiidae) and Sitophilus oryzae (Linnaeus) (Coleoptera: Curculionidae), three important insect pests of stored products. We determined the mortality of O. mercator and L. serricorne exposed to 100-400 ppm at 50 ppm increments for one hour. We also determined the mortality of S. oryzae adults exposed to 200 ppm ozone at different depths within wheat mass in PVC pipes for 6, 12, 18, or 24 h. Mortality was recorded as percentage of insects that died by day 0 (immediately after ozone treatment), day 1, and day 2 post-treatment. Generally, mortality in O. mercator and L. serricorne increased with an increase in ozone concentration. Also mortality was generally higher when insects were treated in the presence of food compared to when treated in the absence of food. For each exposure duration investigated, higher mortality was recorded in S. oryzae adults at 5 cm depth compared to other depths. In addition, the longer the exposure period, the higher the mortality recorded at the various depths. The work reported suggests that ozone treatment could be a fumigant alternative for the management of adults of O. mercator, L. serricorne, and S. oryzae.