Cotton at three stages of crop phenological development was infested with eggs and third instar larvae of the fall armyworm, Spodoptera frugiperda (J.E. Smith), to determine the effect of larval feeding on fruit damage and yield. Regression analyses indicated that numbers of damaged squares and bolls were significantly (P ≤ 0.05) influenced by the number of eggmasses and third instars placed on the plants. More damage resulted with infestations of third instars than with eggs. Fruiting structures that were penetrated tended to have lower probabilities of survival to harvest than did non-penetrated or undamaged fruit. In a subsequent study with individual larvae confined for 48 h by cotton bags on fruiting structures, third instars damaged 0.63 squares, 0.72 small bolls, and 0.40 large bolls; fourth instars damaged 0.71 squares, 0.76 small bolls, and 0.63 large bolls; and fifth instars damaged 0.83 squares, 0.81 small bolls, and 0.66 large bolls. Damage to squares by all instars resulted in a significant (P ≤ 0.05) reduction in survival of fruit to harvest. Feeding on small bolls by fourth and fifth instar larvae, but not third instar larvae, resulted in significant (P ≤ 0.05) reductions in probability of harvest. Feeding on large bolls did not reduce the probability of survival of fruit to harvest.
