Effect of site location and collecting period on the chemical composition of Hyptis spicigera Lam. an insecticidal essential oil from north-Cameroon

Hyptis spicigera essential oils from seven localities in the North-Cameroon (Ngaoundere, Guirvidig, Kodeck, Lara, Toloum, Kaele, Tchecal-baila) were investigated by GC and GC/MS. Results showed differences within harvesting sites and between the different sites of collection but did not revealed clear tendencies in the evolution of the oil composition with regard to the sampling period. The main group of compounds in all the analyzed samples were: alpha-pinene (11.9%-42.1%), beta-pinene + sabinene (6.0%-39.8%) and beta-phellandrene + 1,8-cineole(8.8%-27.4%) except in one oil where beta-caryophyllene (23.4%) was the principal component. The insecticidal activity of H. spicigera and its principal terpenic components was evaluated against the cowpea weevil Callosobruchus maculatus F., the major cause of damages of cowpea (Vigna unguiculata (L.) Walp) in North Cameroon.