VARIATION IN PHASE POLYMORPHISM IN THE COMMON CUTWORM, SPODOPTERA-LITURA (LEPIDOPTERA, NOCTUIDAE)

By changing the rearing conditions of different instars on an artificial diet, it was reconfirmed that larvae of the common cutworm, Spodoptera litura were sensitive to density during the fourth and fifth instars and exhibited phase characters in the last (sixth) instar: those from crowded rearing, but isolated during the last instar, had a greater degree of melanization, recovered more quickly from feigned death when dropped, and fed for shorter periods than those reared completely in isolation. There was a great variability in response to density between groups of larvae originating from different batches of eggs collected in the field. Only a few groups showed the typical responses to density for the three phase characters mentioned above, while most groups indicated characters which were slightly altered, and manifested low density-type responses even at high density. One group invariably showed high density-type responses, having a high degree of melanization, quick recovery from feigned death and relatively short feeding periods. Another group exhibited a yellowish brown colour and fed longer in both rearing conditions, but rarely showed feigned death, flipping over to normal position immediately after being dropped, instead. A crossing experiment revealed that the density response patterns of phase characters in S. litura are under genetic control.