Fumigant effect of sweet basil (Ocimum basilicum L) leaf essential oil on the longevity and fecundity of adult cowpea bruchid Callosobruchus maculatus (F) and on germination

Abstract

Fresh pulverised leaves (600g) of Ocimum basilicum (L) were harvested in July, 2014. Essential oil yield from the hydro-distilled leaves after 3 hours was 0.3(w/w) %. GC/MS analysis revealed the predominance of oxygenated monoterpenes (41.0%) in the oil. Terpinen-4-ol was the major oil constituent accounting for 29.8%. Other significant constituents of the oil were γ-terpinene (9.6%), β – Caryophyllene (7.3%), α-Bergamotene (9.2%) and Sabinene Hydrate (5.0%). The oil was therefore of terpinen-4-ol chemotype. The essential oil (EO) vapour was used to generate an insecticidal atmosphere within airtight fumigation chambers (130ml). Each chamber contained 2 pairs of adult C. maculatus and ten seeds of Ife brown cowpea variety. The EO was tested at 10, 20, 30 and 40µl/130ml air. After 24 hours of exposure, the control had the lowest percentage mortality (0.00) while complete adult mortality was observed in both the 30µl and 40µl doses. The LD₅₀ and LD₉₉ of the EO within 24 hours of exposure were 13.33µl/130ml and 41.38µl/130ml, respectively. However, after 48 hours of exposure, all doses gave 100% mortality and were significantly different (P<0.05) from the control where no mortality was observed. At the end of both exposure periods, significantly (P<0.05) fewer eggs were laid on the oil treated seeds than on the control. There was however no significant difference (P>0.05) in the mean percentage germination of treated and control seeds after 24 and 48 hours.

Keywords: Essential oil, fumigation, Ocimum basilicum, Callosobruchus maculatus, hydrodistillation