Damage Potential of Achaea Janata Linn, at Different Phenological Stages of Castor

Studies on damage potential due to Achaea janala Linn, were carried out at different growth stages of castor (Ricinus communis Vmn.) with differential population of early and late instar larvae. There was significant correlation between larval number and defoliation, yield, yield attributes and oil content. For every unit increase in early and late larval instar, defoliation increased by 2.25 and 21.73 per cent and the reduction in yield was by 1.29 and 23.28 per cent, respectively. Due to heavy defoliation and damage to apical part by the late instar larvae the death of plants increased by 15 per cent with successive increase in larval number at 30 days after sowing (DAS). Such a phenomenon was not evident in respect of early instar. Apart from heavy defoliation and apical part damage, primary spike damage by the later instar larval population was evident at 60 DAS. Among the different yield attributes studied the damage caused to spike and capsules caused significant loss in yield as compared to reduction in foliage at later stage of the crop. Economic injury level (EIL) computed for early and late instar larvae on castor were 1.18 and 0.04,2.84 and 0.15,4.01 and 1.20 and 8.36 and 4.12 larvae plant⁻¹ at 30,60,90 and 120 DAS respectively.