Binary and ternary toxicological interactions of clothianidin and eight commonly used pesticides on honey bees (Apis mellifera)

Authors: WANG, YANHUA - Zhejiang Academy Of Agricultural Sciences; Zhu, Yu Cheng; LI, WENHONG - Guizhou Academy Of Agricultural Sciences; YAO, JIANXIU - Kansas State University; Reddy, Gadi V.P.; LV, LU - Zhejiang Academy Of Agricultural Sciences

Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2021
Publication Date: 7/30/2021
Citation: Wang, Y., Zhu, Y., Li, W., Yao, J., Reddy, G.V., Lv, L. 2021. Binary and ternary toxicological interactions of clothianidin and eight commonly used pesticides on honey bees (Apis mellifera). Ecotoxicology and Environmental Safety. 223:112563. https://doi.org/10.1016/j.ecoenv.2021.112563.
DOI: https://doi.org/10.1016/j.ecoenv.2021.112563

Interpretive Summary: Although many toxicological evaluations have been conducted for honey bees, most of them have focused on the effects of individual pesticides. However, honey bees are usually exposed to pesticide mixtures under field conditions. In this study, we examined effects of exposure to individual compounds and mixtures of clothianidin (CLO) with eight other pesticides [carbaryl (CAR), thiodicarb (THI), chlorpyrifos (CHL), beta-cyfluthrin (BCY), gamma-cyhalothrin (GCY), tetraconazole (TET), spinosad (SPI) and indoxacarb (IND)] on honey bees using a feeding method. Results from toxicity tests of four-day exposure to individual pesticides revealed that CLO had the highest toxicity to bees, followed by IND and CHL. SPI and CAR had relatively low toxicity. Most of the binary mixtures (contains 2 compounds) of CLO with other pesticides exerted additive and antagonistic effects. However, all the ternary mixtures (contains 3 compounds) containing CLO and TET (with the exception of CLO+TET+THD) elicited synergistic responses to bees. Either increased numbers of components in the mixture or/and a unique mode of action appear to be responsible for the higher toxicity of mixtures. Our finding emphasizes the need for risk assessment of pesticide mixtures rather than of the individual chemicals. Our data also provides information that may help growers avoid increased toxicity and unnecessary injury to pollinators.

Technical Abstract: Although many toxicological evaluations have been conducted for honey bees (Apis mellifera), most of these studies have only focused on the effects of individual chemicals. However, honey bees are usually exposed to pesticide mixtures under field conditions. In this study, we examined the effects of individual pesticides and mixtures of clothianidin (CLO) with eight other pesticides [carbaryl (CAR), thiodicarb (THI), chlorpyrifos (CHL), beta-cyfluthrin (BCY), gamma-cyhalothrin (GCY), tetraconazole (TET), spinosad (SPI) and indoxacarb (IND)] on honey bees using a feeding method. Toxicity tests of a 4-day exposure to individual pesticides revealed that CLO had the highest toxicity to A. mellifera, with an LC50 value of 0.24 µg a.i. mL-1, followed by IND and CHL with LC50 values of 3.40 and 3.56 µg a.i. mL-1, respectively. SPI and CAR had relatively low toxicities, with LC50 values of 7.19 and 8.42 µg a.i. mL-1, respectively. In contrast, TET exhibited the least toxicity, with an LC50 value of 258.7 µg a.i. mL-1. Most binary mixtures of CLO with other pesticides exerted additive and antagonistic effects. However, all the ternary mixtures containing CLO and TET (except for CLO+TET+THD) elicited synergistic responses to bees. Either increased numbers of components in the mixture or/and a unique mode of action appeared to be responsible for the higher toxicity of mixtures. Our findings emphasized the need for risk assessment of pesticide mixtures rather than the individual chemicals. Our data also provided information that might help growers avoid increased toxicity and unnecessary injury to pollinators.