Feeding toxicity and impact of imidacloprid formulation and mixtures with six representative pesticides at residue concentrations on honey bee (Apis mellifera)

Authors: Zhu, Yu Cheng; Yao, Jianxiu; Adamczyk, John; Luttrell, Randall

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2017
Publication Date: 6/7/2017
Citation: Zhu, Y., Yao, J., Adamczyk Jr, J.J., Luttrell, R.G. 2017. Feeding toxicity and impact of imidacloprid formulation and mixtures with six representative pesticides at residue concentrations on honey bee (Apis mellifera). PLoS One. 12(6):e0178421. doi:10.1371/journal.pone.0178421.

Interpretive Summary: Imidacloprid is the most widely used insecticide in agricultural. In this study, we used both feeding and spraying methods to simulate in-hive exposures of formulated imidacloprid (Advise® 2FL) alone and mixtures with six representative pesticides for different classes. Advise, fed at 4.3 mg/L (equal to maximal residue detection of 912 ppb in pollen) induced 36% mortality and 56% feeding suppression after 2-week feeding. The additive/synergistic toxicity was not detected from binary mixtures of Advise with different classes of pesticides at residue levels. The feeding of the mixture of all seven pesticides increased mortality to 53%, significantly higher than Advise only but still without synergism. Spray treatments twice a week for 52 days with =1 mg/L and once a week for 2 weeks with 4.3 mg/L Advise showed no adverse effect on bee survival. Concentration at =80 mg/L significantly reduced bee survival. Enzymatic data showed that activities of invertase (honey-making enzyme), glutathione S-transferase (detoxification enzyme), and acetylcholinesterase (insecticide target enzyme) activities in imidacloprid-treated survivors were mostly similar to those found in control. Esterase (detoxification enzyme) activity mostly increased, but was significantly suppressed by Bracket (acephate). The immunity-related phenoloxidase activity in imidacloprid-treated survivors tended to be lower, but most treatments were statistically similar to the control. Increase of cytochrome P450 (detoxification enzyme) activity was correlated with Advise concentrations and reached significant difference at 56 mg/L. Our data demonstrated that residue levels of seven pesticide in pollens/hive may not adversely affect honey bees, but long term ingestion of the maximal residue levels of imidacloprid in pollens (4.3 mg/L) and sulfoxaflor (6 mg/L) may induce substantial bee mortality. Rotating with other insecticides is a necessary and practical way to reduce the residue level of any given pesticide.

Technical Abstract: Imidacloprid is the most widely used insecticide in agricultural. In this study, we used both feeding and spraying methods to simulate in-hive exposures of formulated imidacloprid (Advise® 2FL) alone and mixtures with six representative pesticides for different classes. Advise, fed at 4.3 mg/L (equal to maximal residue detection of 912 ppb in pollen) induced 36% mortality and 56% feeding suppression after 2-week feeding. The additive/synergistic toxicity was not detected from binary mixtures of Advise with different classes of pesticides at residue levels. The feeding of the mixture of all seven pesticides increased mortality to 53%, significantly higher than Advise only but still without synergism. Spray treatments twice a week for 52 days with =1 mg/L and once a week for 2 weeks with 4.3 mg/L Advise showed no adverse effect on bee survival. Concentration at =80 mg/L significantly reduced bee survival. Enzymatic data showed that activities of invertase, glutathione S-transferase, and acetylcholinesterase activities in imidacloprid-treated survivors were mostly similar to those found in control. Esterase activity mostly increased, but was significantly suppressed by Bracket (acephate). The immunity-related phenoloxidase activity in imidacloprid-treated survivors tended to be lower, but most treatments were statistically similar to the control. Increase of cytochrome P450 activity was correlated with Advise concentrations and reached significant difference at 56 mg/L. Our data demonstrated that residue levels of seven pesticide in pollens/hive may not adversely affect honey bees, but long term exclusive ingestion of the maximal residue levels of imidacloprid (4.3 mg/L) and sulfoxaflor (6 mg/L) may induce substantial bee mortality. Rotating with other insecticides is a necessary and practical way to reduce the residue level of any given pesticide.