Effects of Environmental Factors on Phase Variation in Larval Cotton Leafworms, Alabama argillacea (Lepidoptera: Noctuidae)

Abstract
Phase variation in cotton leafworm larvae was characterized using six color categories, ranging from green with yellow longitudinal bands to velvety black. A density-dependent relationship was found between percentage of black larvae and degree of crowding in field-collected larvae. Controlled experiments confirmed that crowding affected degree of larval phase variation. Exposure to crowding during the second and third instar had the greatest effect upon melanization expressed in the fifth instar. Phase variation of crowded larvae reared under photoperiods of LD 14:10 or LD 12:12 were similar. However, the degree of melanization in larvae reared at 18°C was greater than that of larvae reared at 27.5°C.

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