author(s)
Vrushali Pawade, Thakare S. M, Sarita Nehare

abstract
Bt cotton, which confers resistance to important insect pests of cotton, was first adopted in India as hybrids in 2002. Five years later, in 2007 Bt cotton area had soared to 6.2 million ha grown by 3.8 million ha - a remarkably high proportion in a fairly short period of five years. The main objective of this study was field screening of Bt cotton hybrids against H. armigera (Hubner), for which observations of Bt hybrids were undertaken at weekly intervals from 15 to 135 days after emergence for recording larval population and damaged caused by Helicoverpa armigera. The lowest mean neonate larval count per five plants was observed on Tulshi-9 (0.17 to 0.53) followed by RCH-Alto (0.33 to 0.67), JK-99 (0.50 to 1.67) and RCH-2 (0.17 to 0.50) at all levels of observation. In case of percent damage to square, flowers, bolls (fruiting bodies) similar trend was observed. Mallika and MECH-162 recorded comparatively higher number of neonate larvae and percent damage. Tulshi-9 recorded highest yield (15.01 q/ha) followed by JK-99 (11.37 q/ha), RCH-Alto (10.95 q/ha) and Bunny (10.75 q/ha). All the Bt hybrids were found statistically superior over non-Bt in lowering larval count, reducing percent damage and increasing the yield.