Hyptis spicigera, essential oil, chemical composition, insecticidal activity, Sitophilus zeamais.
Abstract :
[en] Overuse of synthetic pesticide raises environmental and health concerns. Researchers are increasingly advocating the use of natural substances to replace them. With this in mind, we set out to study the insecticidal efficacy of Hyptis spicigera essential oil against the maize weevil Sitophilus zeamais The essential oil of H. spicigera was obtained by submitting fresh leaves to steam distillation during 60 min. Oil was analyzed by GC/MS on an apolar column. Insecticidal activity was conducted by fumigation against Sitophilus zeamais. For this, 20 insects aged from 0 to 48 h were separetely exposed to 06 doses of essential oil (5.4, 17.9, 34.6, 53.8, 74.7 and 96.6 ppm) during 72 h. A blank control and a diasphox reference control were also used. Results showed that H. spicigera essential oil was dominated by α-pinene (18.8%), caryophyllene (16.7%), γ-terpinene (13.7%), β-pinene (13.4%) and 1.8-cineole (11.3%). Regarding insecticidal activity, the results revealed that only the highest concentration of essential oil (96.6 ppm) caused significant mortalities: 50.4% after 72 h. For the others, led to low mortalities, which were generally not significantly different to the blank controls at 24 h, although a few isolated differences appeared at 48 h and 72 h. These observations suggest that the efficacy of H. spicigera essential oil should probably be optimised by increasing the dose or testing it by other modes of action. This should allow to obtain a comparable efficacy to that of the reference product.
