author(s)
Md. Niaz Morshed, Mohammad Tofazzal Hossain Howlader, Md. Rafiqul Islam, Naznin Sultana and Md Hasibur Rahaman Hera

abstract
An experiment was carried out under field conditions at the Bangladesh Rice Research Institute, Regional station Sonagazi, Feni, to study the effect of abiotic factors on the seasonal incidence of rice yellow stem borer (RYSB), Scirpophaga incertulas (Walker) and rice leaf folder, Cnaphalocrocis medinalis (Guenee) population at the south-east coastal region of Bangladesh during Kharif-2 (T. Aman), 2019 season. This study aimed to determine the effect of abiotic factors on the incidence of the pest population and to forewarn & plan for timely management of RYSB and rice leaf folder. Insects were collected from the experimental plot by using sweep net method and weather data was recorded simultaneously from the meteorological observatory. Observations on S. incertulas incidence revealed that the highest per cent of dead hearts (10.51) and white heads (9.38) were occurred during the 2nd week of October and 1st week of November, respectively. Per cent, dead hearts incidence were observed highest during the vegetative phase and per cent of white heads were highest during the reproductive phase of the plant. The correlation studies with abiotic factors revealed that temperature showed a negative significant impact on the population of S. incertulas (white heads) and negative non-significant impact on dead hearts. Relative humidity showed a positive significant impact on dead hearts but the negative non-significant impact on white heads. Rainfall showed a positive non-significant impact on dead heart but it showed a negatively significant impact on white heads. Leaf folder infestation attained its peak during 2nd fortnight of October and didn’t get significantly affected by rainfall, relative humidity & temperature. So it is better to take preventive measures for leaf folder from the start of September month. These findings will be helpful for proper and timely management of the rice yellow stem borer & leaf folder in the south-east coastal region of Bangladesh.