Mixture effects of thiamethoxam and seven pesticides with different modes of action on honey bees (Aplis mellifera)

Authors: LI, WENHONG - Guizhou Academy Of Agricultural Sciences; LV, LU - Zhejiang Academy Of Agricultural Sciences; WANG, YANHUA - Zhejiang Academy Of Agricultural Sciences; Zhu, Yu Cheng

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2023
Publication Date: 2/15/2023
Citation: Li, W., Lv, L., Wang, Y., Zhu, Y. 2023. Mixture effects of thiamethoxam and seven pesticides with different modes of action on honey bees (Aplis mellifera). Scientific Reports. https://www.nature.com/articles/s41598-023-29837-w#article-info.
DOI: https://doi.org/10.1038/s41598-023-29837-w

Interpretive Summary: Even though honey bees in the field are routinely exposed to a complex mixture of many different agrochemicals, few studies have assessed toxic effects of pesticide mixtures on bees. In order to clarify the interactive effects of pesticides on crop pollinators, we evaluated the individual and mixture toxicities of thiamethoxam (THI) and other seven pesticides [dimethoate (DIM), methomyl (MET), zeta-cypermethrin (ZCY), cyfluthrin (CYF), permethrin (PER), esfenvalerate (ESF) and tetraconazole (TET)] to honey bees with feeding toxicity test. Results from the 7-day toxicity test indicated that THI displayed the highest toxicity with an LC50 value of 0.25 µg a.i. mL-1, followed by MET and DIM with LC50 values of 4.19 and 5.30 µg a.i. mL-1, respectively. In contrast, pyrethroids and TET exhibited relatively low toxicities with their LC50 values ranging from 33.78 to 1,125 µg a.i. mL-1. Among 98 tested THI-containing binary to octonary mixtures, 29.59% of combinations exhibited synergistic effects, while 18.37% of the mixtures exhibited antagonistic effects against A. mellifera. Moreover, 23 out of 42 pesticide mixtures containing THI and TET displayed synergistic effects on the pollinators. Our findings highlighted that the simultaneous presence of several pesticides might lead to increased toxicity to honey bees. Taken together, these results provided valuable toxicological data on the joint effects of neonicotinoids and other commonly used pesticides in honey bees, which could facilitate further understanding on the potential risks of other coexisting pesticide mixtures in the natural ecosystems.

Technical Abstract: Even though honey bees in the field are routinely exposed to a complex mixture of many different agrochemicals, few studies have surveyed toxic effects of pesticide mixtures on bees. In order to clarify the interactive effects of pesticides on crop pollinators, we evaluated the individual and mixture toxicities of thiamethoxam (THI) and other seven pesticides [dimethoate (DIM), methomyl (MET), zeta-cypermethrin (ZCY), cyfluthrin (CYF), permethrin (PER), esfenvalerate (ESF) and tetraconazole (TET)] to honey bees (Aplis mellifera) with feeding toxicity test. Results from the 7-day toxicity test indicated that THI displayed the highest toxicity with an LC50 value of 0.25 (0.20-0.29) µg a.i. mL-1, followed by MET and DIM with LC50 values of 4.19 (3.58-4.88) and 5.30 (4.65-6.03) µg a.i. mL-1, respectively. In contrast, pyrethroids and TET exhibited relatively low toxicities with their LC50 values ranging from 33.78 (29.12-38.39) to 1,125 (922.4-1,442) µg a.i. mL-1. Among 98 tested THI-containing binary to octonary mixtures, 29.59% of combinations exhibited synergistic effects. In contrast, 18.37% of combinations exhibited antagonistic effects on A. mellifera. Moreover, 23 out of 42 pesticide mixtures containing THI and TET displayed synergistic effects on the pollinators. Our findings highlighted that the simultaneous presence of several pesticides might lead to increased toxicity to honey bees. Taken together, these results provided valuable toxicological data on the joint effects of neonicotinoids and current-use pesticides on honey bees, which could facilitate further understanding on the potential risks of other coexisting pesticide mixtures in the natural ecosystems.