Synergistic mortality between a neonicotinoid insecticide and an ergosterol-biosynthesis-inhibiting fungicide in three bee species

The researchers explored synergisms between the neonicotinoid clothianidin and the demethylation inhibitor fungicide propiconazole in three bee species — the European honey bee (Apis mellifera) the buff-tailed bumble bee (Bombus terrestris)and the solitary red mason bee (Osmia bicornis). The three bee species all have different life history traits, which results in exposure to different levels of pesticides in field settings. Authors obtained dose-response curves for clothianidin in each species, and then utilized the oral LD10 both alone and with a non-lethal dose of propiconazole to test for synergistic effects. Propiconazole was administered at 35 mg/mL (7 µg/bee) and clothianidin doses ranged from 2 to 160 mg/L. For the synergism experiments, bees were exposed to four treatments: control, fungicide, neonicotinoid, and combination of the fungicide and neonicotinoid. Osmia bicornis was the most sensitive to clothianidin. Mortality was assessed four hours after the exposure ended, and then every 24 hours for four days. For honey bees, synergistic effects were seen only at 4 and 24 hours and there was high mortality in the controls, which the authors attributed to working with older forager bees. In bumblebees, synergistic effects were seen only 4 hours after exposure. Clothianidin and propiconazole showed synergism at all assessment times for the mason bees. The biochemical mechanism for synergism was likely related to the fungicide inhibiting cytochrome p450-mediated detoxification (essentially halting an insect’s detoxification system). These results suggest the potential for synergism in bees that are exposed to neonicotinoids and fungicides.

Sgolastra, F., P. Medryzcki, L. Bortolotti, M.T. Renzi, S. Tosi, G. Bogo, D. Teper, C. Porrini, R. Molowny-Horas, and J. Bosch
Pest Management Science
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