Abstract
The study is mainly focused on the morphology of different stages i.e., egg, larvae, pupa and adult. The head capsule measurements (widest head width) were taken by use of Stereozoom binocular microscope. The beet armyworm undergoes 5 instars with a maximum and minimum head width of 0.26 ± 0.01 and 1.70 ± 0.05 mm respectively. The head capsule width of larval instars showed successive increase in a different ratio at each moult and did not follow regular geometrical progression (Dyar's law). Colour polymorphism was clearly observed in the fifth instar of S. exigua recording about 34 morphs with a range of colours i.e., green, black, pink and yellow being dominant with combination of colours and cannibalism also reported in the late instar stages. The total developmental period lasted for 32.38 ± 5.13 days.
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