1. Recent reports on bee health suggest that sublethal doses of pesticides have negative effects on wild bee reproduction and ultimately on their population growth.2. Females of the solitary horned mason bee Osmia cornuta, evaluate thoracic vibrations and odours of males to assess male quality. When certain criteria are met, the female accepts the male and copulates. However, these signals were found to be modified by sublethal doses of pesticides in other hymenopterans. Here, we tested whether sublethal doses of a commonly used fungicide (Fenbuconazole) impact male quality signals and mating success in O. cornuta. Males exposed to fenbuconazole exhibited reduced thoracic vibrations and an al-tered cuticular hydrocarbon profile compared to the control bees. Moreover, males exposed to the fungicide were less successful in mating than control males. Synthesis and applications.Our results indicate that a low toxicity fungicide can negatively affect male reproductive success by altering behavioural and chemical cues. This could explain the decreasing pollinator populations in a pesticidepolluted environment. This study highlights the need for a more comprehensive approach, including behaviour and chemical cues, when testing new pesticides and a more cautionary approach to the pesticides already used on crops.

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