Synergistic effects of three sterol biosynthesis inhibiting fungicides on the toxicity of a pyrethroid and neonicotinoid
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Original Article
Synergistic effects of three sterol biosynthesis inhibiting fungicides on the toxicity of a pyrethroid and neonicotinoid insecticide to bumble bees Aaron IVERSON1,2 , Casey HALE1 , Leeah RICHARDSON1 , Olivia MILLER1 , Scott MCART1 1
Department of Entomology, Cornell University, 4128 Comstock Hall, Ithaca, NY 14853, USA Department of Environmental Studies, St. Lawrence University, 201 Memorial Hall, Canton, NY 13617, USA
2
Received 13 February 2019 – Revised 29 June 2019 – Accepted 18 July 2019
Abstract – Understanding how different pesticides influence bee health is inhibited by a limited knowledge about the interactions between different compounds to which bees are simultaneously exposed. Although research has demonstrated synergistic effects of some sterol biosynthesis inhibiting (SBI) fungicides on the toxicity of certain insecticides to bees, a high degree of variability exists in the relatively few SBI fungicide-insecticide interactions tested. Furthermore, most research has been conducted on honey bees, Apis mellifera , limiting our understanding of pesticide synergisms in native wild bees. We tested the effects of the SBI fungicides difenoconazole, myclobutanil, and fenhexamid on acute contact toxicity of the insecticides thiamethoxam (neonicotinoid) and bifenthrin (pyrethroid) to the common eastern bumble bee, Bombus impatiens . Based on range-finding trials, we selected a single dosage of each pesticide, with insecticides approximating LD20 values and fungicides approximating their maximum sublethal levels. We found that the triazole SBI fungicide difenoconazole interacted synergistically with bifenthrin, with a maximum synergy ratio of 1.48, while the triazole myclobutanil interacted synergistically with both bifenthrin and thiamethoxam, with maximum synergy ratios of 11.0 and 2.38, respectively. However, the hydroxyanilide SBI fungicide fenhexamid did not exhibit a synergistic effect on either insecticide. Our results suggest that certain SBI fungicides, and potentially those from particular SBI classes, may be particularly harmful to bumble bee health when co-exposure to insecticides occurs, despite their low toxicity when experienced in isolation. bee conservation / bioassay / ecotoxicology / pesticide interactions / wild bee
1. INTRODUCTION Unprecedented losses of managed western honey bee (Apis mellifera ) colonies and parallel declines in wild bee populations in recent years have stimulated a wealth of research on potential causes. While several factors are shown to have Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13592-019-00681-0) contains supplementary material, which is available to authorized users.
Corresponding author: A. Iverson, [email protected] Manuscript editor : Monique Gauthier
negative impacts on bee populations, including pathogens, climate change, and habitat loss, agrochemical exposure has surfaced as a major concern, especially in agricultural landscapes (Mullin et al. 2010; Goulson et al. 2015; Koh et a
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