Insecticide Activity of Essential Oils of Mentha longifolia, Pulicaria gnaphalodes and Achillea wilhelmsii Against Two Stored Product Pests, the Flour Beetle, Tribolium castaneum, and the Cowpea Weevil, Callosobruchus maculatus

Essential oils extracted from the foliage of Mentha longifolia (L.) (Lamiales: Lamiaceae) and Pulicaria gnaphalodes Ventenat (Asterales: Asteraceae), and flowers of Achillea wilhelmsii C. Koch (Asterales: Asteraceae) were tested in the laboratory for volatile toxicity against two storedproduct insects, the flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) and the cowpea weevil, Callosobruchus maculatus F. (Coleoptera: Bruchidae). The chemical composition of the isolated oils was examined by gas chromatography-mass spectrometry. InM longifolia, the major compounds were piperitenon (43.9%), tripal (14.3%), oxathiane (9.3%), piperiton oxide (5.9%), and d-limonene (4.3%). In P. gnaphalodes, the major compounds were chrysanthenyl acetate (22.38%), 2L -4L-dihydroxy eicosane (18.5%), verbenol (16.59%), dehydroaromadendrene (12.54%), β-pinen (6.43%), and 1,8 cineol (5.6%). In A. wilhelmsii, the major compounds were 1,8 cineole (13.03%), caranol (8.26%), alpha pinene (6%), farnesyl acetate (6%), and p-cymene (6%). C maculatus was more susceptible to the tested plant products than T castaneum. The oils of the three plants displayed the same insecticidal activity against C. maculatus based on LC(50) values (between 1.54µl/L air in P. gnaphalodes, and 2.65 µl/L air in A. wilhelmsii). While the oils of A. wilhelmsii and M. longifolia showed the same strong insecticidal activity against T. castaneum (LC(50) = 10.02 and 13.05 µl/L air, respectively), the oil of P. gnaphalodes revealed poor activity against the insect (LC(50) = 297.9 µl/L air). These results suggested that essential oils from the tested plants could be used as potential control agents for stored-product insects.