The present study was carried out under the auspices of the Forest Protection Division, Institute of Forest Productivity, Ranchi, India (situated at latitude 23021’26”N, longitude 84014’44”). The field observation was done on O. sanctum grown in the medicinal plant garden of the Institute. The laboratory experiment was carried out in the Forest Entomology Laboratory. The regular observations were taken at weekly intervals for nature of damage, seasonal incidence and percent plant infestation, during 2011 and 2012. To calculate the percent plant infestation, a group of 25 plants was observed and replicated four times randomly in the field. In order to observe the insect population per twig, five twigs (upper 10 cm) from a group of five plants were randomly selected and the insect population was counted and randomly replicated five times in the field. Similarly, to determine the insect population per leaf, five leaves were observed in each plant, the average was calculated, and this observation was replicated in five plants randomly. The observed data were subjected to one-way analysis of variance (ANOVA) using SPSS (PASW-18) statistical analysis software.