Cross-resistance of a chlorpyrifos-methyl resistant strain of Oryzaephilus surinamensis (Coleoptera: Cucujidae) to fumigant toxicity of essential oil extracted from Eucalyptus globulus and its major monoterpene, 1,8-cineole.

The fumigant toxicities of eucalyptus essential oil and 1,8-cineole, the major component of eucalyptus oil, were tested against a chlorpyrifos-methyl resistant strain and a reference strain of the sawtoothed grain beetle, Oryzaephilus surinamensis (L.). The resistant strain showed 1.9- and 2.2-fold higher tolerance against essential oil and 1,8-cineole fumigation toxicity, respectively, relative to the susceptible strain. The increased tolerance for the essential oil may be the result of cross-resistance. The resistance mechanisms in the resistant strain are discussed in relation to elevated detoxifying enzymes such as cytochrome P450 and esterases.