Biological Activity of Rosmarinus Officinalis Essential Oils against Callosobruchus Maculatus, (Coleoptera, Bruchinae)

Abstract

For the purpose of finding alternative ways to synthetic insecticides to fight against pests that ravage stored pulses, rosemary’s (Rosmarinus officinalis (L)) (Lamiaceae) essential oils have been tested against cowpea weevils (Callosobruchus maculatus (Fab)) (Coleoptera, Bruchinae) reared on chickpea (Cicer arietinum (L)) seeds. The chickpea seeds have been infested with ten newly-hatched pairs of cowpea weevils, then fumigated with increasing concentrations of 0, 4, 6, 8 or 10µl of rosemary’s essential oils per liter of air. These essential oils were analyzed by GC-MS. The compound groups were predominantly monoterpenes (93.06%), 74.93% of which were oxygenated and 18.13% hydrocarbonated. The main components in the oxygenated monoterpenes are eucalyptol (1,8-cineol) (50,42%), camphor (17.73%) and borneol (5.99%), while the 3-carene (12.05%) is the most represented compound in the hydrocarbonated  monoterpenes. The remaining constituents represent only 6.94% of essential oils.

Rosemary’s essential oils significantly affect longevity (Treated lot: 1 – 7 days, control lot: 2 – 12 days), fecundity (10 – 48 eggs/10 females vs. 437 – 491 eggs/10 females), and fertility (66.67 – 85.00% vs. 93.75 – 95.44%). The cowpea weevil’s success rates in the treated group were 0 – 60.42% compared to 86.35 – 92.33% in the control lot. The lethal concentrations at 50% (LC₅₀) and 99% (CL₉₉), for exposures between 24 and 120h , ranged from 5.51 – 2.43µl/l of air to 11.24 – 6.33µl/l of air, respectively, for males and from 6.80 – 3.04µl/l of air to 15.74 – 7.44µl/l of air for females. The demographic parameters are significantly affected. The average generation lifespan is prolonged ranging from 33.83 days for the control lots to 36.57 days for the treated lots, while the other parameters were all shortened. Rosemary’s essential oils may be used in an Integrated Pest Management (IPM) of stored legumes without any health or environmental risks.

Keywords: Essential oils, Rosmarinus officinalis, Callosobruchus maculatus, Pulses, Fumigation.