In Vitro Effects of Pesticides on European Foulbrood in Honeybee Larvae.

Sarah C Wood,Igor Medici De Mattos,Elemir Simko,Igor Moshynskyy,Michael W Zabrodski,M Marta Guarna,Tasha Epp,Patricia Wolf Veiga,Ivanna V Kozii,Colby D Klein,Jocelyne C Chalifour

doi:10.3390/insects11040252

Sarah C Wood, Igor Medici De Mattos + Show 9 more

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https://doi.org/10.3390/insects11040252

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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.

Highlights

European foulbrood (EFB), caused by the bacterium Melissococcus plutonius, is an enteric disease of honeybee (Apis mellifera) larvae [1]
When larval survival after infection with 50 colony forming units (CFU) M. plutonius was analyzed using Cox proportional hazard regression (Figure 3), we observed a marginally significant decrease in the survival of larvae exposed to THI and PROP compared to infected controls
We report an atypical isolate of M. plutonius for the first time in Canada

Summary

Introduction

European foulbrood (EFB), caused by the bacterium Melissococcus plutonius, is an enteric disease of honeybee (Apis mellifera) larvae [1]. M. plutonius is transmitted to developing larvae through contaminated brood food and proliferates within the larval midgut, leading to larval death, especially under conditions of colony stress [1]. There is a widespread, chronic, in-hive exposure of honeybees to complex mixtures of agricultural and apicultural fungicides and insecticides through nectar, honeydew, honey, wax, pollen and pollen stored as beebread [12,13,14]. Increased numbers of pesticide residues in wax, fungicides, which inhibit sterol biosynthesis [15], have been significantly associated with colony mortality [13]. There is a concern for the negative effects of chronic, in-hive pesticide exposure on the developing worker brood [16], the transfer of pesticides from pollen and honey to royal jelly is considered to be low, ranging from 0.001%–0.016% [17]

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