Dynamics of leaf feeding by the larvae of rice leaf folderCnaphalocrocis medinalis (Guenee) was studied under greenhouse conditions to develop a feeding test to identify varietal resistance. Area of leaf damaged by larvae during their development indicated that first 3 instars accounted for only 8-06% and V instar alone for 66-3% of the total feeding. In view of the highest feeding rate and the longest feeding duration, V instar was chosen for feeding test. No significant differences in area of leaf damaged were recorded when V instar larvae fed for 48 h on 30, 45 and 60 days old plants or when leaf nitrogen content varied from 2–3·4%. Inherent variability among individual larvae in feeding rate could be maintained within acceptable limits with 5 replications.
The proposed feeding test involved caging of individual V instar larvae for 48 h on 30–45 days old plants of test varieties and recording area of leaf damage. The test revealed varietal differences in area of leaf damaged by the leaf folder and displayed consistency over time. Based on feeding test, 19 rice varieties have been identified as resistant against leaf folder.