Field experiments were conducted in California and Hawaii in order to investigate the relationships between thrips feeding in maize ears and fusarium ear rot and silk-cut symptoms. Half the plots in each experiment were treated with insecticides following pollination. Thrips populations within ears were enumerated at six stages of ear development. Grain was examined microscopically and the percentages of kernels with silk-cut and ear rot symptoms were quantified by weight. Fumonisin B1 contamination in grain was measured by ELISA. Immature stages of thrips predominated, and maximum thrips populations occurred 21 days after pollination. Insecticides reduced thrips numbers, as well as silk-cut, ear rot symptoms and fumonisin B1 contamination. Immature thrips populations were more strongly correlated with silk-cut/ear rot symptoms (R = 0·75) and fumonisin B1 accumulation (R = 0·53), than were adult thrips (R = 0·48 and 0·36, respectively). Silk-cut kernels all had ear rot symptoms and the percentage of kernels with symptoms was highly correlated with fumonisin B1 contamination (R = 0·84). Results suggest that thrips are not occasional feeders, but can complete a substantial portion of their life cycle on maize ears. The results also indicate that thrips activity may be a cause of silk-cut symptoms, and this may be the mechanism that connects thrips activity with fusarium ear rot and fumonisin contamination of grain.