Insecticidal activities of essential oil from the leaves of Mentha longifolia L. subsp capensis against Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae)

Toxicity of the essential oil from the leaves of Mentha longifolia (Lamiaceae) was evaluated against Sitophilus zeamais, an insect that is the major cause of deterioration in stored grains, including maize. The contact, fumigation and repellency bioassays revealed that the oil was toxic to the insect. Increases in oil concentration and time of exposure resulted in a progressive increase in insect mortality. The dose of essential oil at 0.50 mu l/g of maize grains in the contact bioassay caused 100% mortality of S. zeamais, compared to less than 10% mortality recorded at 0.125 mu l/g. The essential oil demonstrated moderate fumigation toxicity against the test insects at concentrations of 24 and 32 mu l of oil per litre of air, respectively. A high repellency was recorded for the oil at all the concentrations tested. Repellency values of as high as 100% were recorded for most concentrations. Mentha longifolia could be a potential agent for the protection of agricultural stored products against S. zeamais.