Assessment of toxicity of fipronil and its residues to honey bees

Laboratory bioassays were conducted to assess the toxicity of fipronil to seven-day-old worker honey bees, using topical and oral applications duplicating likely field exposure. In addition, residual effects of fipronil were assessed after potted cotton plants were sprayed with full and half recommended field rates, exposed to field conditions, then bees were exposed to different age residues. The acute dermal LD50 was 1.9 ng / bee, and acute oral LC50 was 0.4 ng / bee. The residual toxicity of fipronil on cotton leaves remained high for an extended period of 25 d and 20 d for full and half recommended rates of fipronil, respectively. These studies show that fipronil is highly toxic to honey bees via direct spray contact, ingestion, and contact with residues. The application of fipronil in flowering cotton is, therefore, unlikely to be compatible with use of managed honey bees.