Biological studies of Lymantria obfuscata Walker (Lepidoptera: Lymantridae) on apple plantations (Malus domestica Borkh.) in Jammu Region of J & K, IndiaAbstract : Lymantria obfuscata Walker is a polyphagus pest infesting a wide variety of fruit and forest trees. The objective of this work is to study the detailed life cycle of Indian gypsy moth (Lymantria obfuscata Walker) on apple plantations (Malus domestica Borkh.), which is a cherished and economically important fruit crop in Jammu region of J & K State, India and is severely attacked by the larvae off Indian gypsy moths. Larvae defoliate apple plants, reduce their vigour and sometimes the infestation is so severe that it leads to mass destruction of apple plants. Thus, an attempt was made to study the biology of this pest in Jammu as no earlier record of the pest has been obtained from the region so far. Incidence of the pest was determined by the defoliated leaves fallen from the trees which indicates an identification mark for locating the pest. Biological studies include morphometric measurements of different stages from egg to adult. Incubation period varies from 286.0 to 329.0 days (305.2±5.26 days) (mean±SE). Larval period varies from 37 to 60 days (49.8±2.43) days. Pupal period ranges from 12 to 14 days (13.4±0.27 days). Adult longevity of male and female is 3.5 to 6 days (4.45±0.25) and 7 to 9 days (7.60±0.0.20 days) respectively. Besides biology, host plants and distribution of the pest are also included in the paper.