On the food preferences and application of Dyar's law to different hopper instars of Choroedocus illustris Walker (Orthoptera: Acrididae)

Abstract

The influence of diet on different parameters of the life cycle in a pest grasshopper is evaluated. The effect of crowding and temperature on growth of larval stages under the classical model of Dyar is also tested. Brassica oleracea var. botrytis was most preferred by both sexes, with minimum hopper developmental period of 44.00 days in males and 53.60 days in females, while it was prolonged on Andropogon odoratus with the maximum development of 70.90 days in males and 87.90 days in females. Similarly, maximum development of hoppers was 2.31%/day in males, feeding on Brassica oleracea var. botrytis and Paspalum distichum, while it was 1.89%/day in females, feeding on Brassica oleracea var. botrytis. Minimum development of hoppers was observed to be 1.44%/day in males, feeding on Andropogon odoratus, and 1.16%/day in females feeding on Saccharum officinarum and Andropogon odoratus. Dyar's law, applied in lepidopterous larvae, assumes a geometric progression of size measures, and it is significant in the case of acridoids with progressive development through successive formation of instars. Head widths of successive instars were measured separately in both the sexes. The average ratio of increase in each instar for males was 1.264 (minimum) at 27°C under isolated conditions, but increased to 1.309 (maximum) at 37°C under crowded conditions. In female hoppers, the average increase was 1.233 (minimum) at 37°C under crowded conditions and reached up to 1.409 (maximum) at 27°C under the same crowded conditions, before reaching the adult stage.