In experiments to select a character for identifying larval instars in Sesamia calamistis and Eldana saccharina, body length, body width and head capsule width were measured in populations reared on artificial diet. Seven instars were found in S. calamistis and 5 in E. saccharina. For both species, body length was determined to be the best characteristic to distinguish instars because it was easy to measure and had the smallest error.

The cotton boll worm, Heliothis armigera Hbn, was grown under standard conditions. Parameters are given for identification of larval instars on the basis of head capsule width. Intrastadial weight of larvae in terms of fresh weight is presented for a regular time interval of 12 hr. The maximum larval growth in all the stadia was observed in the first 24 hr after the preceding moult. Weight of larvae was almost constant in the last quarter of the stadium, till they moulted into the next. Although the last instar larvae gained maximum weight amongst all the stadia, their actual growth was minimum. First instar larvae recorded a 13 times increase in body weight in comparison to the last instar larvae with 3.9 times. Fifth instar larvae entered into the prepupal stage after they had completed an age of 60 hr. Temperature had a profound influence on the incubation period of eggs; the higher the temperature, the shorter it was. Between 28 and 36°C the incubation period was almost the same. The maximum tolerance level of constant temperature for the eggs of Heliothis armigera was 37°C.

Observations on the growth and development of Chilo partellus (Swinhoe) larvae under laboratory and field conditions indicate sexual dimorphism as well as a general developmental polymorphism. Larvae of both sexes went through fifth, sixth or seventh instars before pupation. The mean developmental period, larval head capsule width, and the number of instars before pupation as well as pupal weight were higher in the female compared to the male larvae. These observations suggest differences in the physiological state of fifth-instar larvae in a population; some of them might be in the penultimate, while others might be in the ultimate instar.

The head capsule widths of larvae of the cowpea pod-borer Maruca testulalis, reared individually and crowded together in the laboratory were measured. The measurements were subjected to a test of analysis of variance, frequency distribution and Dyar's rule. All methods gave a total of five larval instars in the life cycle and conformed to Dyar's rule. There was a high positive correlation (r = 0.97) between the size of the head capsule and the period of development elapsing. The minimum duration of larval development was 9 days.