Chemosensory response of the Phaseolus vulgaris L. (Fabaceae) weevil (Bruchus chinensis Linnaeus, 1758 (Coleoptera: Bruchidae)) to Dioscorea sansibarensis Pax. (Dioscoreaceae) bulbil essential oil

Dioscorea sansibarensis bulbils are well known for their toxicity and medicinal applications. In this study, the attraction and mortality of the Phaseolus vulgaris weevil ( Bruchus chinensis ) caused by Dioscorea sansibarensis bulbil oil was examined in a Completely Randomized Design experiment using a Y-tube olfactometer on a laboratory bench. Statistical analysis at P < 0.05 showed 10 µL had an attraction of 42.67%. In the case of mortality, the results showed that Phaseolus vulgaris seeds treated with 40 µL of the bulbil oil had a harmonic mean of 55.8% mortality of the weevil population, which was higher than with 10 µL of Actellic 50 EC. GC-MS analysis identified 17 compounds in the bulbil oil, the main constituents of which were 2- pentanone, 4-hydroxy-4-methyl- (17.8%), phenol, 4-ethyl- (11.41%), hexadecanoic acid, methyl ester (11.05%), phenol (7.35%), 9-octadecenoic acid, (E)- (7.2%) and phenol, 4-ethyl-2-methoxy- (7.14%). Attraction by bulbil oil may have been due to the presence of phenolic compounds, and mortality may have been due to hexadecanoic acid, methyl ester and 9-octadecenoic acid, (E)-. Attractants are used for the surveillance and detection of an infestation in stored products. The added advantage of the bulbil oil to cause mortality makes Dioscorea sansibarensis bulbil oil useful in the formulation of a botanical pesticide in stored pest management.