Repellence of the main components from the essential oil of Glycosmis lucida Wall. ex Huang against two stored product insects

Abstract A screening of Chinese medicinal herbs and wild plants for agrochemicals was carried out; the essential oil of Glycosmis lucida leaves was found to possess significant repellent activity against Tribolium castaneum and Liposcelis bostrychophila. It was found that the main components included elixene (19.81%), spathulenol (10.68%), anethole (12.05%), verbenone (10.32%) followed by β-caryophyllene (6.87%). The essential oil, anethole and verbenone were strongly repellent against T. castaneum (96, 86 and 94%, respectively, at 15.73 nL cm−2) and L. bostrychophila (100, 68 and 72%, respectively, at 31.58 nL cm−2) after a 2h treatment. The results indicate that anethole and verbenone had the potential to be developed as natural repellents for control of stored product insects.


Introduction
Currently, there is a considerable interest in developing eco-friendly and economically sustainable control methods for stored product pests (Phillips & Throne 2010 essential oils and their constituents have been evaluated for repellent activity against Tribolium castaneum and Liposcelis bostrychophila. Some of them are quite promising in the development of natural repellents (Ukeh & Umoetok 2011;Liang et al. 2013). During the screening programme for new agrochemicals from Chinese medicinal herbs and wild plants, essential oil derived from leaves of Glycosmis lucida Wall. ex Huang (Family: Rutaceae) was found to possess strong repellence against the two stored product insects.
G. lucida is a shrub of the Glycosmis genus that is mainly distributed in Xishuangbanna and western area of Yunnan province, China. It also grows in India and north-eastern Myanmar (Huang 1997). A survey of literature has shown that the chemical composition of genus Glycosmis possessed the insecticidal activities against several insects (Khan et al. 1983;Greger et al. 1996;Latha & Joseph 1999;Yang et al. 2015). This work investigated the chemical composition of G. lucida essential oil and its repellent activity against stored product insects, Tribolium castaneum and Liposcelis bostrychophila.

Chemical composition of essential oil
The GC-MS result of the essential oil of G. lucida gave a yield of 0.35%. A total of 27 components in the crude oil were identified, accounting for 92.2% of the total oil (Table S1). elixene (19.81%), spathulenol (10.68%), anethole (12.05%), verbenone (10.32%) and β-caryophyllene (6.87%) were the major components. There are few literatures on chemical composition of the essential oils from Glycosmis species (Ahmed et al. 2000; Van et al. 2009;Baser & Buchbauer 2010). However, the chemical composition from essential oil of G. lucida was identified by GC-MS for the first time, but further studies on plant cultivation and essential oils standardisation are needed.

Repellent activity
The results of repellent assay for the essential oil of G. lucida leaves and the isolated compounds against T. castaneum and L. bostrychophila are presented in Figure 1. Data showed that at high concentrations, the essential oil, anethole and verbenone strongly repelled the red flour beetle. The essential oil also showed strong repellent bioassay against the booklouse. However, β-caryophyllene demonstrated weak repellence against the two stored product insects. The results showed that the synergistic effect may play an important role in the repellent test.
In previous studies, the fumigant and contact activities of anethole and verbenone have also been demonstrated against the two insects (Rice & Coats 1994;Zhao et al. 2012;Wang et al. 2015). Thus, these two constituents had potential for use as insecticides. Compared with the fumigant and contact toxicity, the repellent effect is an important feature to consider when choosing essential oils or constituents to control pests because the higher the repellence, the lower the infestation, resulting in the reduction or absence of oviposition and, consequently, the number of emerged insects.

Conclusion
Repellent activity of the essential oil, anethole and verbenone were quite promising and they showed potential to be developed as possible natural repellents for control of stored product insects. However, further tests are needed to develop a formulation and to improve the potency and stability of these potential insecticides and repellents for practical use.

Supplementary material
Supplementary material relating to this article is available online, alongside Table S1 and Figure S1.

Disclosure statement
No potential conflict of interest was reported by the authors.  Note: a Means of the same treatment followed by the same letters do not differ significantly (p > 0.05) using tukey's tests at 5% probability level. Pr was subjected to an arcsine square-root transformation before aNoVa and tukey's test.