Relative abundance of different stem borer species in Ahu and Sali rice in Jorhat, Assam

Stem borer complex of rice at the Instructional-Cum-Research Farm, Assam Agricultural University (AAU), Jorhat, Assam, during 2005, comprised of five species of lepidopteran borers viz., the pyralids, Scirpophaga innotata (Walker), S. incertulas (Walker), Chilo suppressalis (Walker), C. polychrysus (Meyrick) and the noctuid Sesamia inferens (Walker). S. innotata was the predominant species followed by S. incertulas while S. inference was the least abundant species of the borer complex. Larval population of S. innotata was 43.39, 41.96 and 35.43 per cent of the total borer population at tillering, maximum tillering and at heading stages of the crop, respectively during the Ahu season, while in Sali season the corresponding percentage was 44.73, 41.48 and 37.50. The population of S. innotata as hibernating larvae was 34.4 per cent. Moth population of S. innotata constituted 73.71 and 72.84 per cent of the total borer complex during Ahu and Sali seasons, respectively. Pink borer, S. inferens was the least abundant species during both the Ahu and Sali seasons.