Single and combined exposure to 'bee safe' pesticides alter behaviour and offspring production in a ground-nesting solitary bee (Xenoglossa pruinosa)

Mounting evidence supporting the negative impacts of exposure to neonicotinoids on bees has prompted the registration of novel 'bee-friendly' insecticides for agricultural use. Flupyradifurone (FPF) is a butenolide insecticide that shares the same mode of action as neonicotinoids and has been assessed to be 'practically non-toxic to adult honeybees' using current risk assessment procedures. However, these assessments overlook some routes of exposure specific to wild bees, such as contact with residues in soil for ground-nesters. Co-exposure with other pesticides may also lead to detrimental synergistic effects. In a fully crossed experiment, we assessed the possible lethal and sublethal effects of chronic exposure to two pesticides used on Cucurbita crops, the insecticide Sivanto Prime (FPF) and the fungicide Quadris Top (azoxystrobin and difenoconazole), alone or combined, on solitary ground-nesting squash bees (Xenoglossa pruinosa). Squash bees exposed to Quadris Top collected less pollen per flower visit, while Sivanto-exposed bees produced larger offspring. Pesticide co-exposure induced hyperactivity in female squash bees relative to both the control and single pesticide exposure, and reduced the number of emerging offspring per nest compared to individual pesticide treatments. This study demonstrates that 'low-toxicity' pesticides can adversely affect squash bees under field-realistic exposure, alone or in combination.