Southwestern Corn Borer (Lepidoptera: Pyralidae) and Fall Armyworm (Lepidoptera: Noctuidae): Comparative Developmental Biology and Food Consumption and Utilization

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Developmental biology and food consumption and utilization of male and female southwestern corn borers, Diatraea grandiosella Dyar, and fall armyworms, Spodoptera frugiperda (J. E. Smith), were compared when reared on a meridic diet. Variations in some developmental parameters were sex-related. Female southwestern corn borer larvae (≥8 d old) and pupae were significantly heavier, had significantly wider head capsules in fourth and fifth instars, and had a significantly longer developmental period than males, but their pupal developmental periods did not differ. In fall armyworm, the only developmental parameter that differed between sexes was the pupal developmental period (Significantly shorter in females). Food consumption and utilization by selected larval age groups were estimated with indices for the amount of food ingested, diet assimilated, approximate digestibility (AD), efficiency of conversion of ingested food (ECI), and efficiency of conversion of assimilated food (ECD). Five-, 7-, and 8-d-old southwestern corn borer males and females had equivalent weight gains, and food consumption and utilization. However, 10-, 13-, and 15-d-old females gained significantly more weight, ingested and digested significantly more food, and had significantly higher ECI and ECD values than comparably aged males. The AD values of these three age groups did not differ significantly between sexes. In contrast, no significant differences in weight gained or in any of the estimated food consumption and utilization indices at all age groups studied were observed between male and female fall armyworm larvae. Thus, variation of developmental biologies of these lepidopterous species are not only speciesrelated but also sex-related. Use of developmental parameters of insects as indicators to measure or compare experimental treatment effects or as criteria for selecting insects to be used in an experiment must be done with caution.