Chemistry and Insecticidal Activity of Essential Oils against Trogoderma granarium Larvae

Abstract

The essential oils from five plants, Mentha spicata, Ocimum basilicum, Cymbopogon schoenanthus, Juniperus phonicea and Matricaria chamomilla were obtained by hydrodistillation and their chemical composition was identified based on spectral analysis of chromatography/mass spectrometry (GC/MS). The insecticidal potential of oils against the larvae of Trogoderma granarium was tested using contact and fumigant toxicity bioassays. Based on GC/MS analysis, the main compounds of essential oils were carvone (66.17 %) in M. spicata, methyl cinnamate (44.28 %) in O.basilicum, piperitone (63.35%) in C. schoenanthus, α-pinene (44.57 %) in J. phoniceaand bisabolol oxide A (56.71 %) in M. chamomilla. It was also clear that the essential oils are rich with monoterpenes, either oxygenated or non-oxygenated ones except the essential oil of M. chamomilla which contains a high concentration of oxygenated sesquiterpenes. The oil of M. spicata displayed the highest fumigant toxicity against T. granarium as, it induced 71.67 and 91.67% larval mortality at 50 and 100 µl/l, respectively, while the essential oil of J. phonicea revealed a weakest toxicity. Among the five tested oils, M. spicata (LC50 = 0.07 mg/cm 2 ), O. basilicum (LC50 = 0.08 mg/cm 2 ) and C. shoenanthus (LC50 = 0.09 mg/cm 2 ) essential oils showed a remarkable contact toxicity against T. granarium. The values of LC50 it is almost half of deltamethrin (0.04 mg/cm 2 ), as one of the recommended insecticides to control stored insect pests. The essential oils of M. chamomilla and J. phonicea displayed moderate and weak contact toxicity, respectively. It was obvious that the essential oils were more active as contact toxicants than as fumigant toxicants. Therefore, M. spicata, O. basilicumand C. shoenanthus essential oils could be implemented in T. granarium management programs.