Genotypes of field-grown corn, Zea mays L., known to vary in their resistance to fall armyworm, Spodoptera frugiperda (J. E. Smith), were used in a study designed to examine the movement of neonate larvae. Movement of larvae was examined on corn plants at the midwhorl (the 8th leaf; V8) stage and the late-whorl (12th leaf; V12) stage. There was little difference in the movement of larvae when they were on resistant ‘MpSWCB–4’ compared with when they were on the susceptible genotype ‘Pioneer 3369A.’ However, larvae reached the feeding sites (whorl tissue) more quickly when they were placed on the younger (upper) leaves than when they were placed on the older (lower) leaves. When larvae were collected from resistant and susceptible genotypes 24, 48, and 96 h after artificial infestation, there were consistently fewer larvae on the resistant genotype only after 96 h. Populations of larvae decreased more rapidly when the plants were infested in the late-whorl stage than when the plants were infested in the midwhorl stage.
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Yang et al. (1993) studied this question.