Abstract
A study was conducted to obtain basic information on the number of larval instars undergone by Spodoptera frugiperda (J. E. Smith) at the Entomology Laboratory of "Nataima" research station of the Colombian Agricultural Institute (I.C.A.) at El Espinal, Tolima. The Regional Research Center has an altitude of 420 m.a.s.l. and an average temperature of 30± 2°C.
Individual observations of larval development and measurements of each instar's head capsule, permited to verify that S. frugiperda has a variation in the number of larval instars. All seems to indicate that such variation was influenced not only by the type and quality of the diet, but also by a genetic factor not jet studied.
First and third generation larvae passed through six instars when feeding on sorghum. Less than 25% of the second generation larvae feeding on 22-25 days old sorghum, underwent seven instars, but if the diet was 36-40 days old, such percentage was 100%. When feeding on sorghum more than 50 days old, between 11% and 50% of the larvae passed through eight larval satages.
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