Identification of host kairomones from maize, Zea mays, for the maize weevil, Sitophilus zeamais

The maize weevil, Sitophilus zeamais, is an economically important pest of stored grains in tropical and subtropical regions of the world. The behavioral responses of adult S. zeamais to volatile organic compounds (VOCs) from maize seeds, Zea mays, were studied to identify semiochemicals used in host location and provide potential tools for managing this pest. VOCs released directly from crude seed extracts, vacuum distilled extracts, hexane and diethyl ether fractions from silica gel chromatography of the vacuum distillates, air entrainment samples, and identified volatile compounds were assayed using a Perspex four-arm olfactometer. Weevils spent significantly more time, and made a higher number of visits, to the region of the olfactometer where Z. mays volatiles were present than in control regions comprising solvent only. When white and yellow Z. mays VOCs were compared in a choice test, the mean time spent in the two olfactometer treatment arms was significantly greater than the mean time spent in the control arms. However, weevils did not show any preference for either of the two treatments, thus demonstrating that both varieties of maize have similar activity. Gas chromatography (GC), coupled gas chromatography-mass spectrometry (GC-MS), GC peak enhancement and electroantennography (EAG) identified hexanal, (E)-2-heptenal, and octanal as biologically active compounds in air entrainment samples and diethyl ether fractions of vacuum distillates. A 3-component synthetic blend of the identified compounds was significantly attractive to both sexes of the weevil. These host kairomones could be deployed in semiochemical based monitoring and management of S. zeamais in the tropics.