The major food for the bees is the pollens and nector which are product from the flowers of the plants . The pollens were available from the Sunflowers during the seasons of flowers farmer use to place the bee hives during those period for pollination and good yields. The bee are the good workers helping farmers to get proper yields and also food to themselves.
The bee get nector from flowers and store in the hive for future purpose some of the flowers like "sesame" has rich in nector to get during the the process they make pollination to plants.
Not only for the crop plants the bees are attracted by the garden plants which also rich in pollens and nector