Plant oils as fumigants and contact insecticides for the control of stored-product insects

The fumigant toxicity of a large number of essential oils extracted from various spices and herb plants was assessed against several major stored-product inserts. Tribolium castaneum (Herbst) was found to be the most resistant, compared with Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Oryzaephilus surinamensis (L.), to most essential oils tested. With the highly active Labiatae sp. oil ZP51, a concentration of 1.43.5 mu l/l air and exposure time of 24 h was enough to obtain 90% kill of all the insects in space tests. In columns 70% filled with wheat, a concentration of 50 mu l/l and 7 d exposure were needed to obtain 94-100% kill of the insects. The biological activity of a number of edible oils, when applied as contact insecticides, was assessed in field studies. Edible oils are potential control agents against Callosobruchus maculatus (F.) and, to a lesser extent against Sitophilus zeamais Motsch., S. oryzae and Sitotroga cerealella (Oliv.). These materials could be very useful on the farm level in developing countries. Plant oils can play an important role in stored-grain protection and reduce the need for, and risks associated with, the use of insecticides. (C) 1997 Elsevier Science Ltd.