MONITORING CHANGES IN COTTON ACREAGE AND ALTERNATE HOST CROPS OF COTTON BOLLWORM USING REMOTE SENSING AND GIS IN MAJOR COTTON GROWING REGIONS OF INDIA
Cotton cultivation has made rapid strides in India since the introduction of Bt cotton, which provided effective protection against its major pest, Helicoverpa armigera and other bollworms. The presence of alternate host crops for cotton bollworms targeted by Bt cotton play a key role in resistance evolution to the in planta expressed Bt proteins. Several host crops for H. armigera such as pigeonpea, sorghum, tomato, chilli, sunflower and corn are cultivated alongside Bt cotton. Change detection in the extent of cotton and alternate host crops of cotton bollworm was conducted using IRS LISS-III data in Punjab, Haryana, Rajasthan, Gujarat, Maharashtra, Andhra Pradesh and Karnataka states. The changes in the extent of cotton and host crops were monitored using multi-temporal data of 2002, 2004 and 2008. The results indicated that Bt cotton (Hirsutum) has almost completely replaced the traditional Indian cotton ( Gossypium arborium). Several alternate host crops of H. armigera were grown along with cotton. Pigeonpea was the major host crop in almost all the locations. Chilies dominated in Andhra Pradesh, sunflower in Karnataka and corn in Gujarat. These host crops serve as ‘natural’ refuge of H. armigera and possibly, for this reason this pest has not evolved resistance to the Bt expressed by Bollgard II even after 16 seasons of intensive cultivation; whereas the pink bollworm, a monophagous cotton bollworm, had developed resistance to Cry1Ac in 2009 and to Cry1Ac and Cry2Ab in 2015.