Fumigant Toxicity of Essential Oils from Basil and Spearmint Against Two Major Pyralid Pests of Stored Products

The fumigant activity of essential oil vapors distilled from sweet basil Ocimum basilicum L. and spearmint Mentha spicata L. (Lamiaceae) were tested against two major stored products pests Ephestia kuehniella (Zeller) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). Various oil doses (0.5, 2.5, 5, 50, 250, 500, 1,000, and 1,500 µl/liter air), for an exposure period of 24 h, were tested. The essential oils were subjected to gas chromatography-mass spectrometry analysis and revealed that the major compounds were for spearmint oil carvone (67.1%) and limonene (+1,8 cineole; 14.3%) and for basil oil linalool (45.9%), 1,8 cineole (16.7%) and eugenol (10.3%). Apart from a few exceptions, no significant differences in insecticidal action were observed between basil and spearmint oil. Both oils were highly effective against adult moths, given that notable mortality (>80%) was recorded after exposure to low doses such as 2.5 µl/liter. Noteworthy, egg mortality was also recorded, reaching 73-79% for basil and 56-60% for spearmint. Toxicity data indicated that larvae and pupae were the most tolerant stages in all cases. Larval mortality never exceeded 21 and 18%, for basil and spearmint, respectively, irrespective of moth species. Basil and spearmint oils displayed mortalities as high as 38 and 28% in pupae. Lethal doses (LD50 and LD99) values were estimated via probit analysis. Developmental stage proved to be a significant factor, whereas the effect of oil species on insect mortality was insignificant. With the exception of adult individuals, basil and spearmint oils did not show satisfactory overall insecticidal activity against E. kuehniella and P. interpunctella.