Persistent effect of a preparation of essential oil from Xylopia aethiopica against Callosobruchus maculatus (Coleoptera, Bruchidae)

Cowpeas, Vigna unguiculata (Walp), are commonly attacked by Callosobruchus maculatus (Coleoptera, Bruchidae) during storage. Current methods to prevent losses during storage involve synthetic insecticides. Although they have insecticidal efficiency, these products have adverse effects on consumers and the environment. Plant products such as those of Xylopia aethiopica (Annonaceae) are potential sources of natural insecticides. This study assessed the efficiency of a preparation of the essential oil of X. aethiopica mixed with its powdered fruits in order to increase the persistence of its effect against C. maculatus. The persistence relates to toxicity against adults, the prevention of F1 emergence, oviposition and the development of eggs laid by C. maculatus. Four treatments were compared: 1) control, consisting of 200 g of grain, 2) 200 g of grain mixed with 2 g of powder from X. aethiopica, 3) 200 g of grain mixed with 0.4 ml of essential oil, and finally 4) 200 g of grain mixed with 2 g of powder plus 0.4 ml of essential oil. The results showed that, with powder alone, crude essential oil, and powder imbibed with essential oil, the toxicity lasted respectively for 3, 9 and 12 days (p<0.05). The persistence of the effect of treatment with X. aethiopica powder plus essential oil on the mortality and oviposition of C. maculatus was better than that of the treatment with the crude essential oil (p<0.05 until day 18). Moreover, the X. aethiopica powder enriched with essential oil provoked, after 52 days, 100% of development inhibition. The hatching of eggs of C. maculatus was also inhibited by all the formulations except the control. The authors results indicate that protection of cowpeas against C. maculatus may be possible using a formulation based on the dry fruits of X. aethiopica; the powder may increase the persistence of the essential oil.