Population Dynamics of Spodoptera exigua (F.) and S. litura (F.) in Soybean

This study on the population dynamics of Spodoptera exigua (F.) and S. litura (F.) in soybean was done with observations made from 10 days after germination of the crop for two years. The results revealed that these pests are more abundant from July to August- Spodoptera litura (F.) occurred from the first week of July with occurrence of adults increasing with the growing season, and ending with the maturity of the crop. Amongst the current, 1st lag and 2nd lag week weather parameters, the occurrence of adults of S. exigua revealed a significant positive correlation with minimum temperature (r=0.716), evening relative humidity- RH (r=0.535), sunshine (0.621) and wind speed (0.661). Maximum temperature and wind speed exhibited a significant negative correlation with incidence of males of S. litura whereas, morning and evening RH were positively correlated with the incidence at 1-lag and 2-lag weeks. The incidence of larvae of S. litura was significantly influenced by morning RH (r=0.783) in the 2-lag week. The regression equation indicated that an increase in 1 mm rainfall decreased the male moth catches of S. exigua; while, incidence of larva was significantly affected with increase in 1% of morning RH; and incidence of S. litura larvae was related with maximum temperature of 1oC.