Acute Toxicity of Fungicide–Insecticide–Adjuvant Combinations Applied to Almonds During Bloom on Adult Honey Bees

Abstract

Beekeepers report significant honey bee deaths during and after almond bloom. These losses pose a major problem for the California almond industry because of its dependence on honey bees as pollinators. The present study aimed to determine if combinations of pesticides applied during almond bloom during daylight hours were a possible explanation for these losses. In this study we aimed to mimic the spray application route of exposure to pesticides using a Potter Spray Tower to treat adult honey bees with commonly encountered pesticides and pesticide combinations at multiples of the maximum recommended field application rates. Tested insecticides included Altacor® and Intrepid®, and tested fungicides included Tilt®, Pristine®, Luna Sensation®, and Vangard®. Synergistic toxicity was observed when the fungicide Tilt (active ingredient propiconazole) was applied with the insecticide Altacor (chlorantraniliprole), though neither caused significant mortality when applied independently. The study also looked at the effect of adding a spray adjuvant, Dyne‐Amic®, to pesticide mixtures. Dyne‐Amic was toxic to honey bees at concentrations above the maximum recommended field application rate, and toxicity was increased when combined with the fungicide Pristine (pyraclostrobin and boscalid). Addition of Dyne‐Amic also increased toxicity of the Tilt and Altacor combination. These results suggest that application of Altacor and Tilt in combination with an adjuvant at the recommended field application rates could cause mortality in adult honey bees. These findings highlight a potential explanation for honey bee losses around almond bloom, emphasize that the safety of spray adjuvants to bees should not be assumed, and provide support for recommendations to protect bees from pesticides through application at night when bees are not foraging. Environ Toxicol Chem 2022;41:1042–1053. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Selected Biochemical Markers Change after Oral Administration of Pesticide Mixtures in Honey Bees

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Are fungicides a driver of European foulbrood disease in honey bee colonies pollinating blueberries?

“…Decreased survival from pathogen infection in response to fungicide exposure may be explained by decreased immune function (O'Neal et al, 2018). Furthermore, proprietary ingredients present in these fungicide products may also contribute to the increased larval EFB mortality observed after exposure to multiple fungicides, as pesticide adjuvants have been previously implicated in enhancement of pesticide toxicity to honey bees (Mullin et al, 2015;Walker et al, 2022).…”

Using the Honey Bee (Apis mellifera L.) Cell Line AmE‐711 to Evaluate Insecticide Toxicity

“…Two or more insecticide formulations are frequently mixed and then applied in a single application (i.e., tank mixing). Tank mixing is convenient and can improve pest control, but these mixtures, which likely include adjuvants, may result in additive or synergistic toxicity for honey bees (Wade et al, 2019 ; Walker et al, 2022 ). Furthermore, formulations are themselves a blend of active and inert ingredients.…”