Please have a look at these useful links.

https://www.researchgate.net/publication/263850390_Pollinator_fauna_and_foraging_activity_of_honey_bees_in_two_genotypes_of_Bt_cotton

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0072988

http://www.alabees.com/impact_of_honey_bee_pollination_.htm

Article Pollinator fauna and foraging activity of honey bees in two ...

Please go through these PDF attachments also.

Thank you, Dr. Arvind Singh

There is no difference wrt honey bee activity on bt and non bt versions.The same number is vaialble in both biotypes. However , since Bt cotton flowers little earliar than non bt versions, this mau give indiaction of more no. on bt cottton.If we go for staggered planting for same hybrid with bt and non bt versions in such way that they bear flowers at the same time, virtually no difference shall appear wrt activity/population in both types.