Investigating the use of herbicides to control invasive grasses in prairie habitats: Effects on non-target butterflies

Invasive grasses severely impact prairies in the northwestern United States, leading to the decline of several butterfly species. Controlling these invasive species is a high priority for land managers. The use of herbicides is a promising management technique, yet effects on non-target butterflies are virtually unknown. We conducted a field investigation on the effects of a widely used grass-specific herbicide on butterfly habitat and demography using the Puget blue (Icaricia icarioides blackmorei Barnes and McDunnough) butterfly as a model species. Habitat use of adult silvery blue (Glaucopsyche lygdamus Doubleday), ochre ringlet (Coenonympha tullia Müller), and wood nymph (Cercyonis pegala Fabricius) butterflies was also quantified. The results indicate that the herbicide had very little to no impact on larval survival, flower species, or Puget blue oviposition, while adult butterflies spent significantly less time in sprayed plots than in controls. Given the necessity of invasive grass control in natural areas, we recommend several strategies to minimize herbicide effects on butterflies.