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In Vitro Effects of Pesticides on European Foulbrood in Honeybee Larvae

1
Department of Veterinary Pathology, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK S7N 5B4, Canada
2
Beaverlodge Research Farm, Agriculture and Agri-Food Canada, 1 Research Road, Beaverlodge, AB T0H 0C0, Canada
3
National Bee Diagnostic Centre, Grand Prairie Regional College, 1 Research Road, Beaverlodge, AB T0H 0C0, Canada
4
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, 52 Campus Drive, Saskatoon, SK S7N 5B4, Canada
*
Author to whom correspondence should be addressed.
Insects 2020, 11(4), 252; https://doi.org/10.3390/insects11040252
Received: 2 March 2020 / Revised: 12 April 2020 / Accepted: 14 April 2020 / Published: 17 April 2020
Neonicotinoid and fungicide exposure has been linked to immunosuppression and increased susceptibility to disease in honeybees (Apis mellifera). European foulbrood, caused by the bacterium Melissococcus plutonius, is a disease of honeybee larvae which causes economic hardship for commercial beekeepers, in particular those whose colonies pollinate blueberries. We report for the first time in Canada, an atypical variant of M. plutonius isolated from a blueberry-pollinating colony. With this isolate, we used an in vitro larval infection system to study the effects of pesticide exposure on the development of European foulbrood disease. Pesticide doses tested were excessive (thiamethoxam and pyrimethanil) or maximal field-relevant (propiconazole and boscalid). We found that chronic exposure to the combination of thiamethoxam and propiconazole significantly decreased the survival of larvae infected with M. plutonius, while larvae chronically exposed to thiamethoxam and/or boscalid or pyrimethanil did not experience significant increases in mortality from M. plutonius infection in vitro. Based on these results, individual, calculated field-realistic residues of thiamethoxam and/or boscalid or pyrimethanil are unlikely to increase mortality from European foulbrood disease in honeybee worker brood, while the effects of field-relevant exposure to thiamethoxam and propiconazole on larval mortality from European foulbrood warrant further study. View Full-Text
Keywords: European foulbrood; Melissococcus plutonius; atypical; honeybee; neonicotinoid; fungicide; thiamethoxam; boscalid; pyrimethanil; propiconazole European foulbrood; Melissococcus plutonius; atypical; honeybee; neonicotinoid; fungicide; thiamethoxam; boscalid; pyrimethanil; propiconazole
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Wood, S.C.; Chalifour, J.C.; Kozii, I.V.; Medici de Mattos, I.; Klein, C.D.; Zabrodski, M.W.; Moshynskyy, I.; Guarna, M.M.; Wolf Veiga, P.; Epp, T.; Simko, E. In Vitro Effects of Pesticides on European Foulbrood in Honeybee Larvae. Insects 2020, 11, 252.

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