Comparative evaluation of the chemical composition and bioactivities of essential oils from four spice plants (Lauraceae) against stored-product insects

Spices are popular commodities with highly edible and medicinal values. At ancient times, people took advantage of spices to prevent insect infestation and mold erosion in stored-products. The Lauraceae family offers abundant raw materials as spices and plants from this family have widely biological activities. Here, the essential oils (EOs) of four spice plants from the Lauraceae, namely Cinnamomum burmannii, Cinnamonuun migao, Litsea pungens and Laurus nobilis were analyzed for their chemical composition by GC-MS. The EOs and some of their individual components mainly monoterpenoids were evaluated for their bioactivities against stored-product insects. Three modes of action were selected: fumigant, contact toxicity and repellent activity. Target insects were adults of Tribolium castaneum and Liposcelis bostrychophila. Results of GC-MS analysis denoted that the chemical composition of EOs from these spice plants had certain similarity and diversity. All the EOs were rich in monoterpenoids, and the major components were limonene, sabinene, linalool, eucalyptol, borneol, alpha-terpineol, 4-terpinenol, alpha-terpinyl acetate, beta-caryophyllene, spathulenol and 1,2,3,4-tetramethylbenzene. The results of bioassays indicated that all the EOs were toxic and repellent to T. castaneum and L. bostrychophda. Common monoterpenoids limonene, sabinene, linalool, eucalyptol, borneol, alpha-terpineol, 4-terpinenol and alpha-terpinyl acetate showed different levels of insecticidal or repellent activities against the two insect species. Among these monoterpenoids, borneol had no fumigant toxicity, but possessed contact toxicity and beneficial repellency at the concentration range of 63.17-2.53 nL/cm(2) against L bostrychophila. Sabinene and alpha-terpineol were significantly repellent to T. castaneum within the testing concentration range of 78.63-3.15 nL/cm(2). Furthermore, beta-caryophyllene (sesquiterpenoids) and 1,2,3,4-tetramethylbenzene (aromatics) were also assessed. beta-caryophyllene exhibited contact toxicity and repellency against T. castaneum and L. bostrychophila. 1,2,3,4-tetramethylbenzene was toxic to these target insects in fumigant and contact assays. This work provides some evidence for explaining insecticidal and repellent activities of several spices from the Lauraceae based on individual active substances. It suggests that these spice EOs have promising potential to serve as bio-insecticides and green repellents for controlling pest damage in warehouses and grain stores.