Coconut is one of the major crops of commercial importance among the palms. The leaf-eating caterpillar Opisina arenosella Walker is the most important lepidopteran pest of coconut palm in India and Sri Lanka. Assessment of crop loss is essential for a realistic planning for research and developmental policies. Information on the yield loss in coconut due to O. arenosella attack is very meagre. In the present study, results of investigations carried out on leaf-eating caterpillar-induced yield loss in coconut palms in Kerala, India, for a period of 4 years (2002–2005) are presented. A maximum crop loss of 45.4% in terms of nut yield was recorded from infested palms in the succeeding year of severe pest incidence. The infested palms also showed reduction in bunch and leaf production to the tune of 21.0 and 13.8%, respectively. The pest-attacked palms regained their normal yield potential by the fourth year after heavy pest infestation.
