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Summary
The distance between the frontal setae (DFS) of the larval head capsule is suggested as a parameter for identifying the larval instar of Lepidopteran species. This parameter is more accurate and convenient than other parameters commonly used for this purpose, and can be easily applied to biological and ecological studies. Six Lepidopteran species of four different families were studied using this parameter. The rate of increase of the DFS is geometric and independent of the temperature. There is no overlapping between the groups of the DFS of successive instars.
The noctuid species studied here usually had six larval instars. A certain proportion of the population had an additional moult which caused reduction in the rate of increase and in the ratio between successive instars. Larvae of the other families studied went through five instars only.