Two Honduran landrace sorghum (San Bernardo III and Manzano-177) [Sorghum bicolor (L.) Moench] populations were evaluated to determine the effects of plant age on fall armyworm (Spodoptera frugiperda (J.E. Smith) development and mortality. A laboratory feeding study was initiated with leaf material 24, 68, and 111 days after plant emergence. Larvae that fed on whorl leaves of older plants suffered higher mortality and required longer time for development than those that fed on younger plants. Larval weight at 7 days of age was 16-fold higher when reared on leaf material from younger plants compared with leaf material from older plants. The innate capacity for increase was about twofold higher on younger plants compared with the older plants, the latter having a lower per cent N and water content. The detrimental effect of older plants on fall armyworm development may explain, in part, the low numbers of this pest from August through November on Honduran photosensitive sorghums planted during the "primera" (first rainfall cycle, April through July).