Seasonal Occurrence of Major Defoliators, Sucking Pests and Natural Enemies in Soybean and their Association with Rainfall

Abstract

Soybean is one of the most important oilseed crops, but its productivity is severely constrained by the seasonal occurrence of insect pests and their interaction with prevailing weather conditions. Information on the population dynamics of major soybean insect pests, their natural enemies, and their association with rainfall under the agro-climatic conditions of Vidarbha is limited, making it difficult to develop timely and location-specific pest management strategies. Therefore, a field experiment was conducted during the Kharif seasons of 2019–20 and 2020–21 at the Agriculture Research Station, Achalpur, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra, India, to investigate the seasonal occurrence of major defoliators, sucking pests, and natural enemies in soybean and their association with rainfall. Weekly observations were recorded on major insect pests, including leafhopper (Amrasca biguttula biguttula), whitefly (Bemisia tabaci), girdle beetle (Obereopsis brevis), green semilooper (Chrysodeixis acuta), and tobacco leaf-eating caterpillar (Spodoptera litura), along with important natural enemies such as ladybird beetles, green lacewings, and spiders. The results revealed that the incidence of leafhopper and whitefly commenced during the 31st SMW, with peak populations occurring during the 37th and 38th SMWs, respectively. Girdle beetle infestation commenced during the 34th SMW and reached its maximum during the 37th and 36th SMWs in 2019–20 and 2020–21, respectively. Among the defoliators, green semilooper and tobacco leaf-eating caterpillar attained peak populations during the 37th and 39th SMWs, respectively. Correlation analysis revealed a non-significant association between rainfall and most insect pests during both cropping seasons. However, the spider population showed a significant positive correlation with rainfall during 2020–21 (r = 0.652). Natural-enemy populations fluctuated throughout the cropping period in correspondence with pest activity. The findings indicate distinct seasonal patterns in the occurrence of soybean insect pests and their natural enemies, while rainfall was significantly associated only with spider abundance during 2020–21.