Geometrics of growth in four species of Spodoptera.
Four species of Spodoptera (Noctuidae: Lepidoptera) viz., S. litura (F.), S. mauritia Boisduval, S. exigua (Hub.) and S. frugiperda (J.E. Smith) were reared on castor, rice, chickpea and on artificial diet, respectively under laboratory conditions during 2017-2019 at the Department of Entomology, College of Agriculture, PJTSAU, Rajendranagar, Hyderabad. The observations on the geometrics of growth in terms of width of head capsule (widest head width) confirming to Dyar's law were made. In S. litura the linear growth ratio was 1.45 confirming a regular geometrical progression in the consecutive larval instars. In S. mauritia and S. frugiperda it was 1.62 and 1.94, respectively; but in S. exigua it was observed to vary as 1.41 (between 1st and 2nd instars), 2.61 (2nd and 3rd instars), 1.05 (3rd and 4th instars) and 1.64 (4th and 5th), with a mean of 1.68, and slightly deviating from Dyar's law. In specific, it was of the ratio of 2.61 between 2nd and 3rd instars showing the maximum progression factor, and confirming the variation among the four species evaluated.