Lethal levels of ozone for all stages of insects

BACKGROUND: Gaseous ozone (O₃) has potential for control of insects in stored grain. Previous studies have focused on freely exposed insects. Immatures of internal pests (e.g. Sitophilus spp. and most stages  of Rhyzopertha dominica F.) are protected within kernels and probably require higher doses and/or longer treatment times for full control. A laboratory study determined the doses of ozone necessary for full control of freely exposed and internal stages of eleven stored-product pest species. Test insects were three species of Sitophilus, R. dominica, Tribolium confusum Jacquelin du Val, T. castaneum Herbst, Plodia interpunctella Hübner, Sitotroga cerealella Olivier, Oryzaephilus surinamensis L., Ephestia kuehniella Zeller and Stegobium paniceum L. Insects were exposed to continuous flows of ozone in doses of 10–135 ppm and exposure times of 5–8 days. Dose-mortality bioassays were conducted on three species of Sitophilus and P. interpunctella.

RESULTS: Freely exposed stages (with a few exceptions) were controlled with 35 ppm of ozone for 6 days. Full mortality of internal stages within kernels required exposure to 135 ppm for 8 days.