From the Telegraph:
They set up a controlled experiment in Punjab earlier this year comparing the behavior and productivity of bees in two hives – one fitted with two mobile telephones which were powered on for two fifteen minute sessions per day for three months. The other had dummy models installed.
After three months the researchers recorded a dramatic decline in the size of the hive fitted with the mobile phone, a significant reduction in the number of eggs laid by the queen bee. The bees also stopped producing honey.