Evaluation of the insecticidal effect of the extracts of six plants (Maesa lanceolata, Solanum syzymbrifolium, Annona squamosa, Cymbopogon citratus, Ocimum basilicum and Ocimum gratissimum) contre les Sitophilus

Abstract

With a view to developing a strategy for the integrated management of pests associated with cereals in stock in Kivu in the Democratic Republic of Congo, the insecticidal activity of the six plants (M. Lanceolata, S. Syzymbrifolium, A. Squamosa, C. citratus O. Basilicum and O. Gratissimum) on the survival of sitophilus weevils infesting maize and rice was studied under controlled conditions. The extracts mainly the phenol-tannin mixture for the following plants: C. Citratus, O. Basilicum and O. Gratissimum and the flavonoid-terpene mixture for the following plants: M. Lanceolata, S. Syzymbrifolium, A. Squamosa dissolved in 1% ethanol was applied at 0.2; 0.02 and 0.002 g.mL-1. Compared to controls, our extracts significantly affect the survival of weevils, depending on the concentration and duration of exposure. Corrected mortality ranged from 67% to 90% for extracts of C. Citratus, O. Basilicum and O. Gratissimum; 69% to 100% for extracts of M. Lanceolata, S. Syzymbrifolium, A. Squamosa. Weevils respond to the toxic effects of the tested compounds, with the LD50 ranging from 0.10 to 0.44 and the LD90 from 0.22 to 0.95 gmL-1. It is the extracts of M. Lanceolata, S. Syzymbrifolium, A. Squamosa which proved to be the most toxic compared to the other extracts.