In vitro effects of pesticides on european foulbrood in honeybee larvae
Citation
Wood, S.C., Chalifour, J.C., Kozii, I.V., de Mattos, I.M., Klein, C.D., Zabrodski, M.W., Moshynskyy, I., Guarna, M.M., Veiga, P.W., Epp, T., Simko, E. (2020). In vitro effects of pesticides on european foulbrood in honeybee larvae. Insects, [online] 11(4), http://dx.doi.org/10.3390/insects11040252
Plain language summary
Exposure to agrochemicals has been linked to immunosuppression and increased susceptibility to disease in honey bees. European foulbrood (EFB) is a disease of honey bee 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 the bacterium that causes EFB, Melissococcus plutonius. With this isolate from a blueberry-pollinating colony, we developed an in vitro larval infection system to study the effects of pesticide exposure on the development of EFB disease. We found that, individual, field-realistic residues of the insecticide thiamethoxam and/or the fungicides boscalid or pyrimethanil are unlikely to increase mortality from EFB, while the effects of field-relevant exposure to insecticide thiamethoxam and fungicide propiconazole on larval mortality from EFB warrant further study. This study reports the identification of an atypical variant of the bacterium that causes European foulbrood disease, and the development of an in vitro infection model to evaluate the expression of disease in the absence and presence of agrochemicals encountered by honey bees during pollination.
Abstract
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.