Data for national-level pesticides consumption shows no dramatic decrease in pesticide use after Bt cotton came in unlike the popular claim.

http://eands.dacnet.nic.in/At_Glance_2010/15.2.xls

2001-02 (first year of illegal Bt cotton cultivation?): 47.02 thousand tonnes of TG materials;
2002-03: (first year of approved bt cotton cultivation): 48.30
2003-04: 41.00
2004-05: 40.67
2005-06: 39.77
2006-07: 41.51 (mealybug first appearance?)
2007-08: 44.77
2008-09: 43.86

OFFICIAL FIGURES SHOW NO DRAMATIC DECREASES IN PESTICIDES CONSUMPTION AS CAN BE SEEN ABOVE. THIS INCIDENTALLY IS VERY DIFFERENT FROM THE NUMBERS THAT EVERYONE CITES, ATTRIBUTING IT TO KESHAV KRANTHI, CICR, WITHOUT MENTIONING WHERE IT WAS PUBLISHED!

The value-related data in crores of rupees is available from CICR as quoted in the DTE report also:

http://www.downtoearth.org.in/dte/userfiles/images/20l_31072011.jpg (this shows a three-fold increase in the cost of pesticides in India across crops, all over the country. One and half times increase in insecticides use in agriculture; 47% increase in insecticides in cotton alone, in the decade of Bt cotton expansion in the country!.
(courtesy: Kavitha Kuruganti, ASHA)