Chemical composition of Cupressus lusitanica and Eucalyptus saligna leaf essential oils and bioactivity against major insect pests of stored food grains

The leaf essential oils from Cupressus lusitanica, Miller and Eucalyptus saligna, Smith obtained by hydrodistillation were analyzed by GC/MS and also screened for their insecticidal and repellent effects against adult Tribolium castaneum, Acanthoscelides obtectus, Sitotroga cerealella and Sitophilus zeamais. The C. lusitanica oil contained mainly umbellulone (18.38%) and α-pinene (9.97%) whereas the E. saligna oil was dominated by α-pinene (24.40%) and 1,8-cineole (24.26%). Bioassays showed that of the four insect species tested, A. obtectus and S. cerealella were the most susceptible to the oils, with LC50 values of 0.05-0.11% v/w in contact toxicity and 4.07-7.02μl/L air in space fumigation. Except in T. castaneum with percentage repellence (PR) values of 65-92.5%, the other test insects recorded PR values less than 30%. The PR values decreased with exposure time in all insects except in T. castaneum. Our results show that C. lusitanica and E. saligna essential oils are promising insecticides and repellents to be used against insect pests of stored food grains.