Population Dynamics of Yellow Stem Borer Scirpophaga incertulas Walker

Population dynamics of the rice yellow stem borer (Scirpophaga incertulas Walker) was evaluated at the Regional Agricultural Research Station, Pattambi, Kerala, for 27 years (1997 to 2023) using regression models. The weekly distribution data showed two prominent time periods of peak incidence- first during the (10^th-16^th) standard meteorological week (SMW) and 38^th-48^th SMW. There was a significant negative correlation of incidence during peak incidence i.e. 12^th SMW with maximum temperature (TMAX), minimum temperature (TMIN), morning relative humidity (RH I), and evening relative humidity (RH II). During 43^rd SMW incidence revealed a negative association with TMIN, RH I and RH II. Multiple linear regression model of incidence at 12^th peak week with weather variables TMAX, TMIN, RH I and SSH revealed a R² value of 0.83. Composite regression indicated a significant interaction effect of temperature and relative humidity for the peak periods of 10^th -16^th and 38^th-48^th SMW’s; these models yielded higher model accuracy than multiple linear regression models. The distribution of incidence for the 12^th and 43^rd peak week i.e. low, medium and high was studied using multinomial logistic regression models, which had an accuracy of 92 and 72%, respectively.