Insecticidal Drimane Sesquiterpenes from Warburgia ugandensis against Maize Pests

Abstract

Sitophilus zeamais and Prostephanus truncatus, the destructive pests of maize in Africa, cause extensive tunneling in maize grain leading to conversion of maize grain into flour within a very short time. Small-scale farmers are often forced to sell maize shortly after harvest to minimize losses during storage, thereby attract low prices and compromising food security. Most available pesticides have adverse effects on environment and humans. The aim of this study was to evaluate efficacy of extracts and compounds of Warburgia ugandensis in controlling of S. zeamais and P. truncatus. Chromatographic fractionation of extracts from W. ugandensis afforded 7α-acetylugandensolide (1), ugandensolide (2), polygodial (3), warbuganal (4), ugandensidial (5), mukaadial (6) and muzigadial (7). The structures of the compounds were determined using spectroscopic and physical methods. n-Hexane extract was the most repellent among the extracts while polygodial (3) was the most repellent compound against the two pests. n-Hexane and ethyl acetate extracts caused 76.3-78.3% and 71.1-75.0% deaths of the insects respectively. Polygodial (3) and warbuganal (4) caused 64.3-70.0 and 61.7-65.0% deaths respectively. n-Hexane and ethyl acetate extracts, polygodial (3) and ugandensolide (2) significantly inhibited the emergence of the insects. The findings from this study show that extracts from W. ugandensis are effective in controlling maize insect pests.