Bioactivities of cymol and essential oils of Cupressus sempervirens and Eucalyptus saligna against Sitophilus zeamais Motschulsky and Tribolium confusum du Val

The essential oils extracted from Eucalyptus saligna and Cupressus sempervirens leaves were analysed by GC-MS and evaluated along with cymol, one of their main constituents for their repellent and toxic effects on Sitophilus zeamais and Tribolium confusum. Contact toxicity assayed by impregnation on filter paper discs or coating onto maize grains showed that these chemicals caused significant mortality of the test insects. Eucalyptus oil was more toxic than Cupressus oil to both insect species (LD50=0.36 μl/cm2 for S. zeamais and 0.48 μl/cm2 for T. confusum) on filter paper discs, and was more toxic to S. zeamais on maize (LD50=38.05 μl/40 g grain). Both oils considerably reduced the F1 progeny production and grain weight loss. Moreover, both crude oil extracts produced a stronger repellent activity against the test insects than did cymol. These results suggest that the essential oils from E. saligna and C. sempervirens may be used in grain storage against insect pests.