Repellent and insecticidal activities of Hyptis suaveolens (Lamiaceae) leaf essential oil against four stored-grain coleopteran pests

Abstract

We evaluated the contact toxicity, fumigant toxicity and repellency of the essential oil of Hyptis suaveolens (L.) leaves against adults of four stored-product coleopteran pests, namely Callosobruchus maculatus (Bruchidae), Rhyzopertha dominica (Bostrychidae), Sitophilus oryzae (Curculionidae) and Tribolium castaneum (Tenebrionidae). Four major compounds were identified in the oil by gas chromatography: sabinene (41.0%), terpinen-4-ol (12.31%), β-pinene (10.0%) and β-caryophyllene (8.0%). Oil concentrations of 0.05–2.0% were tested on adult coleopterans for contact toxicity by topical application. Repellency was evaluated at 0.4–18.3 mg/cm 2 concentrations using an area preference test, whereas fumigant toxicity of the oil was tested both in air and admixed with grain at 1–50 μl/l air and 25–100 μl/l, respectively. Persistence of the oil admixed with grain was tested at 0.1–2.5% concentrations for a period of 40 days. Percentage repellence ranged from 20.0 to 94.7% at 5 h against the test insects at the highest dose tested (18.3 mg/cm 2 ). Adults of C. maculatus were the most susceptible in both contact and fumigant toxicity assays, with an LD 50 value of 57.0 μg/mg weight of insect and an LC 50 value of 4.7 mg/l air, respectively. The oil had low persistence. H. suaveolens leaf essential oil may have potential as an alternative to the synthetic pesticides used in the treatment of grain in storage.