Chemical composition of Cupressus lusitanica, miller and eucalyptus Saligna, smith essential oils and bioactivity against lepidopteran and coleopteran pests of stored grains

Abstract

The chemical composition of C. lusitanica and E. saligna essential oils was determined and leaf essential oils evaluated for contact and fumigant toxicity, repellence and reproduction inhibition effects against S. cerealella, A. obtectus, S. zeamais and T.castaneum. Bioassays were carried out at temperature of 28±2oC and relative humidity of 65±5% and laid out in CRD with four replicates per treatment. In all bioassays, essential oils were applied at 0.00, 0.05, 0.10, 0.15 and 0.20% v/w except fumigation. In the instant contact toxicity, oil was applied on wheat and bean or maize grains in 100 ml glass jars. In the residual contact toxicity oils were applied as above but for treated grain storage duration of 30-120 days. In the space fumigation, oils were applied at 0, 5, 10, 15 and 20 μlL-1 air in a space fumigation chamber whereas in grain fumigation oil was assayed at 0, 30, 50, 70 and 100 μlL-1 air and test insects exposed to oils for 3-10 days. In instant repellency, oils were assayed in an alternate untreated -treated bioassay system whereas in residual repellence oils were assayed as above but treated grain was stored for 30-120 days. In reproductive inhibition test insects were allowed to lay eggs in petri-dishes lined with filter papers soaked in test oils. Leaves yielded the highest amount of oil, 0.31% in E. saligna and 0.35% in C. lusitanica. In C. lusitanica essential oil, -pinene (38.1 %) α-pinene (23.9 %)-phellandrene (10.8 %) dominated in fruit, bark and leaves, respectively whereas in E. saligna p-cymene (26.8 %), sabinene (12.1%) and borneol (5.1%) dominated in leaves, fruit and bark respectively. In instant and residual contact toxicity, C. lusitanica and E. saligna essential oil caused mortality of 5-93.0 and 19.7- 89.5 %, respectively. In space and grain fumigation C. lusitanica and E. saligna essential oils caused mortality of 18.5-100 and 2.3-100 %, respectively. In instant repellence, C. lusitanica and E. saligna essential oil elicited percentage repellence (PR) values of 30-92.5 and -10-9.3 % but in residual repellence bioassay, oils produced PR values of 37.9-51.1 and 34-52.4%, respectively. Percent progeny reduction in C. lusitanica and E. saligna essential oils was 50- 100 and 58 - 100 %, respectively. The effects of C. lusitanica and E. saligna on the insect pests of stored products are manifold, hence promising insecticides and repellents to be used against insect pests of stored grains. Therefore, with more bioactivity studies on more insects and policies in place on formulation and application protocols, the oils might find a place in insect pest control.