Imidacloprid and Fipronil induced abnormal behavior and disturbed homing of forager honey bees Apis mellifera
Naznin Nahar, Takeshi Ohtani
Pesticides may be one of causes of recent decline of honey bees (Apis mellifera). They may affect the orientation and ability of bees to return to the hive. We investigated the effect of sub-lethal doses of imidacloprid and fipronil on behavior and homing ability of bees. Foragers were injected with different concentrations of insecticides to determine the sub-lethal doses. For imidacloprid, 2, 5 and 10 ng/forager and for fipronil, 1, 5 and 10 ng/forager were found sub-lethal. Foragers caught from hive entrance were injected with sub-lethal doses to observe their homing. Imidacloprid and fipronil induced abnormal behaviors. Treated foragers showed trembling, tumbling, abnormal fanning and grooming, restless running, being stationary, lying on its back and lack of co-ordination. Foragers injected with imidacloprid spent 12.3 minutes on grooming whereas foragers treated with 5 ng fipronil spent 13.8 minutes beingrnstationary. Imidacloprid treated foragers took 54 minutes to recover whereas fipronil treated foragers took 38 minutes. After recovery, foragers were released from 50 m away from the hive to see whether they can come back. Treated foragers showed reduced homing rate. Maximum foragers failed to come back hive. Almost all control foragers were found inside the hive in the next morning of release whereas only few foragers of 10 ng imidacloprid and 5 ng fipronil treated were found. We assume that imidacloprid and fipronil are responsible for bee loss by hampering homing of foragers.