Composition and Efficacy of Zanthoxylum alatum Essential Oils and Extracts Against Spodoptera litura

Abstract

Zanthoxylum alatum Roxb. (Z. armatum DC.), belonging to the family Rutaceae, is a large genus of over 200 species of aromatic plants, in which 10 species are reported in India [1]. The species distributed in the hot valleys of the subtropical Himalayas is an important shrub that is traditionally and medicinally used in “kapha” and “vata,” abdominal and dental problems, leucoderma, asthma, and in fever and dyspepsia due to their deodorant, disinfectant, and antiseptic properties [2]. Many researchers have reported that the essential oil and extract exhibited good antimicrobial, insecticidal, larvicidal, anthelmintic, and antiinflammatory properties and are also useful in gastric ulceration [3–8]. The bark and seeds of the shrub are generally used by the local inhabitants of the subtropical Himalayas to treat toothache and pyorrhea. The literature survey revealed the chemical composition of essential oils from the leaves, terminal branchlets, fruits, and pericarp [9–13]; earlier, 10–12% oil yield in the fruit pericarp was also reported by the researcher [13]. Dubey and Purohit [11] reported the presence of linalool (34.5%) as a major constituent in the leaf oil of Z. alatum. The presence of linalool to an extent of 87.7% and 70.6%, respectively, has also been reported [14, 15]. Recently, linalool (18.8%) and undecan-2-one (17.0%) from the aerial parts of Z. alatum were also reported [16]. In this communication, the efficacy of essential oils and extracts of Z. alatum were tested against Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), which is an economically important polyphagous pest with high mobility and reproductive capacity [17]. It is one of the most economically important insect pests in many countries including India, Japan, China, and other countries of Southeast Asia. In India, China, and Japan, its larval stages causes damage up 30% of crops, including tobacco, castor, groundnut, tomato, cabbage, cauliflower, cotton, and other cruciferous crops [18, 19]. About 71% of groundnut (A. hypogaea L.) has been affected with increased larval density of S. litura in India [20] and intensified defoliation [21]. Synthetic organic insecticides damage the environment and lead to pest resurgence, pest resistance to insecticides, and lethal effects on nontarget organisms [22]. To overcome this problem, one needs to develop ecofriendly and biodegradable antifeedant/ insecticides. Extensive surveys and reports on plants used as insecticides/antifeedant can be found in the literature. More than 2400 plants species have been reported to have insecticide/antifeedant properties [23]. Extensive literature survey shows that analysis of bark essential oil of Z. alatum as well as antifeedant activity against S. litura has not been previously conducted. The present study is therefore aimed at investigating the essential oil constituents of the leaves, bark, and pericarp of Z. alatum and the efficacy of its extracts and oils against larvae of S. litura. The essential oils of Z. alatum were subjected to detailed GC and GC-MS analyses in order to determine the variations in plant organs; 0.5, 0.3, and 13.0% oil yields in leaves, bark, and fruit pericarp, respectively, were obtained. The identified compounds in all the oils are shown in Table 1 in order of their elution pattern. The major constituents of the leaf oil were 2-undecanone (43.1%), linalool (33.4%), -pinene (5.9%), 2-tridecanone (5.3%), and -phellandrene (4.3%), while in bark oil, 2-undecanone (38.0%), -pinene (25.0%), 2-tridecanone (15.0%) and trans-caryophyllene (5.3%) were found to be the most abundant compounds. Earlier it was reported that linalool (18.8%) and undecan-2-one (17.0%) were the major components from the aerial parts of Z. alatum [16]. Our fruit pericarp oil afforded linalool (45.2%), limonene (19.6%), -phellandrene (14.4%) and methyl cinnamate (9.3%) as the major constituents. The content of linalool in the pericarp oil was reported to be from 70.6– 87.7% in some earlier studies [13–15].