ROLE OF PHENOLICS IN RESISTANCE OF MAIZE GRAIN TO THE STORED GRAIN INSECTS, PROSTEPHANUS-TRUNCATUS (HORN) AND SITOPHILUS-ZEAMAIS (MOTSCH)

Phenolics in maize, Zea mays L., grain were assessed as a possible factor or indicator of resistance to two stored product insect pests. Weight loss of grain of seven maize genotypes due to Prostephanus truncatus (Horn) (Coleoptera:Bostrichidae) was found to be strongly and negatively correlated to the phenolic content of maize grain determined by high pressure liquid chromatography (HPLC) [r = -0.93, P(r > -0.93) = 0.01]. Similarly, using 25 Mexican landraces, grain weight loss due to Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) was determined to be negatively correlated to total phenolics in the grain [r = -0.84, P(r > -0.84) = 0.01) as measured by a new and rapid quantitative imaging technique. The technique employed microspectrofluorimetry to quantify intense fluorescence due to phenolics in milled grain samples or to locate fluorescence in cross sections of whole grains. In whole grains, fluorescence was most intense in the aleurone layer, pericarp and embryo but less intense in the endosperm. These localizations were confirmed by HPLC of extracts of the various tissues.