Toxicity of Schizonpeta multifida essential oil and its constituent compounds towards two grain storage insects.

Background: The essential oil derived from the flowering aerial parts of Schizonpeta multifida was investigated for insecticidal activity against two grain storage insects, maize weevil (Sitophilus zeamais) and red flour beetle (Tribolium castaneum).

Results: The main constituents of the essential oil were menthone (40.34%) and pulegone (26.87%), followed by D-limonene (5.81%) and isomenthone (5.14%). Bioactivity-directed chromatographic separation on repeated silica gel columns led to the isolation of menthone and pulegone. Pulegone showed pronounced contact toxicity against S. zeamais and T. castaneum adults (7 day LD(50)= 4.46 and 1.55 µg per adult respectively) and was more toxic than menthone (7 day LD(50)=33.47 and 2.67 µg per adult respectively), while the crude essential oil had 7 day LD(50) values of 30.17 and 2.75 µg per adult respectively. Pulegone also displayed strong fumigant toxicity against S. zeamais and T. castaneum adults (7 day LC(50)=3.47 and 11.56 mg cm(-3) respectively) and was again more toxic than menthone (7 day L(50) =10.32 and 31.25 mg cm(-3) respectively), while the crude essential oil had 7 day LC(50) values of 8.33 and 26.41 mg cm(-3) respectively.

Conclusion: The essential oil of S. multifida and its two main components may have potential to be developed as new natural fumigants/insecticides for the control of stored product insects.