Data from: Co-exposure to a honeybee pathogen and an insecticide: Synergistic effects in a new solitary bee host but not in Apis mellifera

Pesticides and pathogens are major drivers of bee declines. However, their
potential interactions are poorly understood, especially for non-Apis
bees. This study assessed the combined effects of infestation by the
honeybee pathogen Vairimorpha ceranae and chronic exposure to the
insecticide flupyradifurone on Osmia bicornis and Apis mellifera. We
investigated whether V. ceranae could reproduce in a new solitary bee host
(O. bicornis) and assessed sublethal and lethal effects of the pathogen
and the pesticide, alone and in combination. We also analyzed the
interactive effects of the combined exposure on V. ceranae proliferation
and bee survival in the two bee species. Newly-emerged bees were orally
infected with 100,000 spores of V. ceranae and then exposed ad libitum to
flupyradifurone at field-realistic concentrations. We showed, for the
first time, that V. ceranae can replicate in the midgut of O. bicornis,
causing histological damage, impaired phototactic response, reduced food
consumption, and decreased longevity. The pathogen-pesticide combination
caused a synergistic effect in O. bicornis, leading to an abrupt survival
decline. In A. mellifera, V. ceranae and flupyradifurone showed
antagonistic survival effects, but the pesticide promoted pathogen
proliferation. Our results warn against the potential effects of pathogen
spillover and multiple stressor exposure on non-Apis bees.