Fumigant Activity and Chemical Composition of Three Essential Oils Used in Gelatin Capsules for the Control of Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae) in Egypt

The objective of this study was to test the use of plant volatiles as a simple, safe and effective technology for postharvest insect pest control. Specifically, the fumigant action of the three local plant essential oils, namely Cinnamomum sp. (Lauraceae), Eucalyptus sp. (Myrtaceae), and Salvia officinalis L. (Lamiaceae), were tested against Acanthoscelides obtectus (Coleoptera: Chrysomelidae), which has recently become a major pest of dry beans in Egypt. To test the efficacy of each oil, 7 μl was added to a piece of filter paper at various concentrations (4–11 %) and then placed inside a perforated gelatin capsule. This technique was used to eliminate direct contact between the volatile oils and stored beans (to avoid any adverse effects to beans). At 48 h post-treatment, adult insect mortality was significantly increased for all tested oils relative to the untreated control. Based on probit analysis at 48 h post-treatment, the Cinnamomum sp. essential oil was the most effective (LC50 = 4.55 %; 4.23–4.89 %). Eucalyptus sp. (LC50 = 7.47 %; 7.15–7.80 %) and S. officinalis (LC50 = 7.57 %; 7.20–7.96 %) had similar but lower efficacies. The main component in Cinnamomum sp. oil was (E)-cinnamaldehyde (a phenylpropene), while in Eucalyptus sp. oil it was 1,8-cineole (eucalyptol), and in S. officinalis oil they were eucalyptol and camphor (terpenoids). The fumigant activity of the tested oils is attributable to their richness in volatile phenylpropene and terpenoids. The gelatin capsule is a simple yet effective technique that could be used in integrated pest management programmes for postharvest treatments, but further testing is required, especially in small-to-medium storage environments.