Fumigant toxicity of essential oils and their constituent compounds towards the rice weevil, Sitophilus oryzae (L.)

Toxicity of various essential oils and their volatile constituents towards the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), was determined. The most potent toxicity was found in essential oil from eucalyptus (LD50 = 28.9 mul/l air). GC-MS analysis of essential oil from eucalyptus showed it to be rich in 1.8-cineole (81.1%), limonene (7.6%) and alpha -pinene (4.0%). Treatment of S. oryzae with each of these terpenes showed 1,8-cineole to be most active (LD50=23.5 mul/l air). In addition to 1,8-cineole, benzaldehyde (LD50 = 8.65 mul/l air) occurring in peach and almond kernels had a potent fumigant toxicity towards the rice weevils. Therefore, benzaldehyde and other natural volatiles could be a safer fumigant to control stored-grain insect pests than those currently used. (C) 2001 Elsevier Science Ltd. All rights reserved.