Population Fluctuation of Bihar Hairy Caterpillar, Spilarctia obliqua (Walker) and its Natural Enemies on Castor Under Semi-Arid Conditions of Gujarat, India

Bihar hairy caterpillar, Spilarctia obliqua (Walker), is a polyphagous lepidopteran pest, known to cause substantial damage to a wide range of agricultural and horticultural crops. In recent years, its occurrences have become increasingly severe in castor (Ricinus communis L.) cultivation in Western India. Therefore, to study the seasonal incidence and damage potential, a study was undertaken on castor (GCH-8) during Kharif, 2024–25, at the Centre for Oilseeds Research, S. D. Agricultural University, Sardarkrushinagar. The results revealed that peak larval incidence (43.52 larvae/plant) was observed during the 45^th SMW, coinciding with maximum foliar damage (58.44%) during the 44^th SMW. The larval parasitoid, Cotesia ruidus (Wilkinson), was recorded from natural field infestations in castor. The highest population (1.60 spiders/plant) of spider (adult and spiderling) was recorded at 49^th SMW, and the maximum (1.00 coccinellids/plant) coccinellids (adults) were recorded during 44^th SMW, and the maximum population of Chrysoperla (1.40 Chrysoperla/plant) was recorded during 44^th SMW. Multiple regression analysis revealed that abiotic factors had a strong influence on pest incidence, particularly larval population (R² = 0.66) and leaf damage (R² = 0.61) while, natural enemies showed weak to moderate relationships (R² = 0.18-0.45), indicating a greater role of abiotic factors.