FALL ARMYWORM (LEPIDOPTERA, NOCTUIDAE) LARVAL GROWTH AND SURVIVORSHIP ON SUSCEPTIBLE AND RESISTANT CORN AT DIFFERENT VEGETATIVE GROWTH-STAGES

Two single-cross com, Zea mays L., hybrids (Mp701 x Mp706 and Mp496 x Mp707) with leaf-feeding resistance at the midwhorl stage of growth to fall armyworm, Spodoptera frugiperda (J. E. Smith), were evaluated for resistance from seedling (V3) to pretassel (V14) vegetative stages. Expression of resistance was determined by comparing the growth and survivorship of fall armyworm larvae reared for 7 d on the resistant hybrids and on a susceptible hybrid (Ab24E x SC229). Larvae recovered from infested seedlings of the resistant hybrids weighed 43% less than those recovered from the susceptible hybrid. When plants were infested in the early-, mid-, and late-whorl stages (V6, V8, and V12, respectively) significantly fewer larvae or smaller larvae (or both) were obtained from the resistant hybrids than from the susceptible hybrid. However, when the plants were infested at pretassel stage of growth (V14), differences in larval growth and survivorship were smaller and more inconsistent. Differences in larval weight between resistant and susceptible hybrids were greater when plants were infested at earlier whorl stages. No consistent differences were found among plant growth stages within either resistant or susceptible hybrids for weight or survivorship.