Occurrence of maize stem borer complex influenced by weather conditions along with an altitudinal gradient in Nepal

Newly constructed black light traps (BLT) were placed in an open maize cropping area at Rampur in Chitwan (228 masl), Puranchaur (900 masl) and Lumle (1750 masl) in Kaski district of Nepal. Traps were operated at weekly interval from dusk to dawn in fixed day throughout the year for two consecutive years 2017 and 2018, and trapped borer insects recorded. Stem borers complex (Chilo partellus Swinhoe and Sesamia inferens Walker) were found in the study areas. Maximum number of C. partellus (103) moths was trapped in the month of March at Rampur, followed by Lumle (28) and Puranchaur (25) during the month of April with mean temperature ranged 18-24ºC. Similarly, the highest numbers of S. inferens (51 and 33) moths were trapped during the month of November at Rampur and Puranchaur; 22 at Lumle area during October at mean temperature range of 14-21ºC, respectively. This study clearly indicated that C. partellus was mostly active in summer and S. inferens in winter season in all three ecological regions. These results clearly showed that the incidence of borer complex was found more in the lower elevation>300 masl than in the foot hill, 900-1000 masl and the high hill, 1700-1800 masl. Occurrence of the adult of C. partellus was positively correlated with maximum temperature (r=0.248) and minimum temperature (r=0.751) but negatively corrected with rainfall (r=-0.172) while negatively correlated with maximum temperature (r =-0.652), minimum temperature (r=-0.233) and rainfall (r=-0.575) in the case of S. inferens.