Abstract
The screening of several Chinese medicinal plants for insecticidal principles showed that essential oil of Rhododendron anthopogonoides flowering aerial parts possessed significant toxicity against maize weevils, Sitophilus zeamais. A total of 37 components were identified in the essential oil and the main constituents of the essential oil were 4-phenyl-2-butanone (27.22%), nerolidol (8.08%), 1,4-cineole (7.85%), caryophyllene (7.63%) and γ-elemene (6.10%), followed by α-farnesene (4.40%) and spathulenol (4.19%). Repeated bioactivity-directed chromatographic separation on silica gel columns led us to isolate three compounds, namely 4-phenyl-2-butanone, 1,4-cineole, and nerolidol. 4-Phenyl-2-butanone shows pronounced contact toxicity against S. zeamais (LD50 = 6.98 μg/adult) and was more toxic than either 1,4-cineole or nerolidol (LD50 = 50.86 μg/adult and 29.30 μg/adult, respectively) against the maize weevils, while the crude essential oil had a LD50 value of 11.67 μg/adult. 4-Phenyl-2-butanone and 1,4-cineole also possessed strong fumigant toxicity against the adults of S. zeamais (LC50 = 3.80 mg/L and 21.43 mg/L) while the crude essential oil had a LC50 value of 9.66 mg/L.
Highlights
Control of stored product insects relies heavily on the use of synthetic insecticides and fumigants, which has led to problems such as disturbance of the environment, increasing application costs, pest resurgence, pest resistance to pesticides and lethal effects on non-target organisms in addition to direct toxicity to the users [1]
During a screening program for new agrochemicals from Chinese medicinal herbs and local wild plants, the essential oil derived from flowering aerial parts of Rhododendron anthopogonoides Maxim. (Family: Ericaceae) was found to possess strong insecticidal activity against the maize weevil, Sitophilus zeamais Motsch
We report the isolation of three components derived from this essential oil active against the maize weevil and the chemical composition and insecticidal activities of the essential oil of
Summary
Control of stored product insects relies heavily on the use of synthetic insecticides and fumigants, which has led to problems such as disturbance of the environment, increasing application costs, pest resurgence, pest resistance to pesticides and lethal effects on non-target organisms in addition to direct toxicity to the users [1]. Various workers have been concentrating their efforts on the search for natural products as an alternative to conventional insecticides and fumigants, as well as the re-evaluation of traditional botanical pest control agents [4,5,6,7,8,9,10,11]. During a screening program for new agrochemicals from Chinese medicinal herbs and local wild plants, the essential oil derived from flowering aerial parts of Rhododendron anthopogonoides Maxim. No compounds active against stored product insects were isolated from the essential oil of R. anthopogonoides so far.
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