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

Abstract

Imidacloprid is the most widely used insecticide in agriculture. In this study, we used feeding 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 active ingredient [a.i.] in pollen) induced 36% mortality and 56% feeding suppression after 2-week feeding. Treatments with individual Bracket (acephate), Karate (λ-cyhalothrin), Vydate (oxamyl), Domark (tetraconazole), and Roundup (glyphosate) at residue level had a mortality range of 1.3–13.3%, statistically similar to that of control (P>0.05). 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. 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 (12 ppm a.i.). 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 (912 ppb) and sulfoxaflor (3 ppm a.i.) may induce substantial bee mortality. Rotating with other insecticides is a necessary and practical way to reduce the residue level of any given pesticide.

Long‐term risk assessment on noneffective and effective toxic doses of imidacloprid to honeybee workers

“…After weekly treatment for three weeks, honeybees treated with 552 mg/L Advise (imidacloprid) showed significantly higher AChE activity than water‐only control, while other concentrations maintained similar AChE activity to that of control. These data confirmed our previous findings (Zhu et al, ) that also showed no significant change in AChE activity after both feeding treatment and spray treatment with imidacloprid formulation. But, the AChE activity was induced in bees treated with higher concentrations of imidacloprid in this study.…”

“…These data confirmed our previous findings (Zhu et al, 2017a(Zhu et al, , 2017b ) that also showed no significant change in AChE activity after both feeding treatment and spray treatment with imidacloprid formulation. But, the AChE activity was induced in bees treated with higher concentrations of imidacloprid in this study.…”

“…After 24 hr, higher concentration consistently reduced more bee weight than low concentration of imidacloprid treatment (Figure ). Previously, we found significant suppressions of honeybee body weight after feeding treatments with 4.3 mg/L of formulated imidacloprid (Advise 2Fl) and residue level of acephate (Yao et al, ; Yao et al, ; Zhu et al, ). The suppression might be caused by significant suppression of ingestion (Zhu et al, ).…”

“…Previously, we found significant suppressions of honeybee body weight after feeding treatments with 4.3 mg/L of formulated imidacloprid (Advise 2Fl) and residue level of acephate (Yao et al, ; Yao et al, ; Zhu et al, ). The suppression might be caused by significant suppression of ingestion (Zhu et al, ). In this study, we confirmed that spray treatments with imidacloprid (Advise 2Fl) also negatively affected honeybee feeding and growth, although the negative impact of feeding treatment was substantially higher than in the spray treatment.…”

“…Also, in‐hive oral exposure may significantly differ from spray exposure, which includes both contact and oral lick by bees. Previously, we determined that feeding treatment of Advise 2Fl at 4.3 mg/L still incurred 36% mortality after 2‐wk long feeding on imidacloprid‐containing sugar solution (Zhu, Yao, Adamczyk, & Luttrell, ). Therefore, our noneffective concentration (912 ppb) may be applied to field spray system.…”