VARIATION IN THE NUMBER OF INSTARS OF Spodoptera frugiperda (J. E. Smith)

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, Toll­ma. The Regional Research Center has an altitude of 420 m.a.s.. and an average temperature of 30± 2°C. Individual observations of larval de­velopment and measurements of each instar's head capsule permitted 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 stages.