Seasonal occurrence of defoliators on soybean and their natural enemies in relation to weather conditions

Abstract

A study was conducted in the kharif season of 2021 and 2022 at the Soyabean Research Farm of BAU, Ranchi, to investigate the seasonal occurrence of pre-dominant lepidopteran insect pests on soybean (Glycine max (L.) Merrill). At different phases of the soybean crop's growth, the tobacco caterpillar (Spodoptera litura Fab.) and green semilooper (Chrysodeixis acuta Walker) were identified as the main defoliator insects causing damage. The peak activity of tobacco caterpillar incidence during kharif, 2021 and 2022 (4.6 and 4.2 larva/mrl) was observed during 37th and 36th SMW respectively whereas the peak activity of green semilooper larva (2.2 and 1.7 larva/mrl) were recorded during 36th and 35th SMW. Correlation studies indicated that tobacco caterpillar has significant correlation with only minimum temperature during 2021 and for green semilooper only rainfall has significant correlation during 2022. The results of the multiple linear regression analysis showed that, for the years 2021 and 2022, respectively, the overall influence of weather parameters was 75.89% (R2 = 0.7589) and 57.80% (R2 = 0.578) on tobacco caterpillars. However, for green semiloopers, it was 75.03 percent (R2 = 7.503) and 19.203 percent (R2 = 0.192) in 2021 and 2022, respectively.