Marathon is a formulation of the neonic insecticide, imidacloprid, that’s commonly used on ornamental plants in nurseries, garden centers, and homes across the US. A 2021 University of California paper shows that the application of Marathon, even at 30% of the recommended dose, killed 90% of leafcutter bees.
Marathon (imidacloprid) used on ornamental plants kills bees
The Green Stars Project 