Characterizing a contentious management tool: the effects of a grass-specific herbicide on the silvery blue butterfly

Abstract

Selective herbicides are a conservation tool employed to reduce invasive vegetation and improve habitat for native plants and animals. However, herbicides may negatively affect non-target organisms such as butterflies through direct chemical exposure or by altering plant community composition and structure. We evaluate the effect of the grass-specific herbicide fluazifop-p-butyl on behavior and demographic responses of the silvery blue butterfly (Glaucopsyche lygdamus) in the field and also quantify effects on reproductive behavior in the greenhouse. We find that in the first few months after an early spring application, herbicide decreases vertical grass structure but does not have a positive or negative net effect on adult behavior, egg deposition, larval density, pupal weight, or ant-tending association for the silvery blue. Our greenhouse oviposition choice trials corroborate field findings and indicate that females do not show preference for unsprayed host plants. Selective herbicides create a vegetative structure preferred by butterflies and do not negatively affect the silvery blue when applied in the early spring. Appropriate timing of herbicide application is likely the key to avoiding adverse effects on vulnerable butterfly life stages. Depending on the longevity of the vegetative reduction, strategic herbicide application may be useful for restoring prairie communities in concert with other restoration tools; however, further testing on additional butterfly species is an imperative precursor to large-scale spraying.