Effects of Herbicides on Oregon Silverspot Butterfly Populations PDF Download

Author: Cassandra F. Doll
Publisher:
ISBN:
Category : Herbicides
Languages : en
Pages :

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Book Description
Herbicides are used as management tools to improve habitat for native plants and animals, but their application may also have harmful effects on the native community. The federally threatened Oregon silverspot butterfly (Speyeria zerene hippolyta) resides in remnant native grasslands along the Pacific Northwest coast. However, like many grasslands, many of these areas are overwhelmed with invasive plants, such as false dandelion (Hypochaeris radicata) and velvet grass (Holcus lanatus). These and other invasive plants severely limit the abundance of the Oregon silverspot’s larval hostplant, the early blue violet (Viola adunca). Selective herbicides, such as clopyralid and fluazifop-p-butyl, can reduce invasive plant abundance. However, non-target effects of these herbicides, and of adjuvants applied with these herbicides, on the Oregon silverspot are unknown. In our study, we applied herbicides and adjuvants to both hostplants and larvae of a subspecies closely related to the Oregon silverspot, the Zerene silverspot (S. z. zerene). Responses measured in two experiments included survival, sex ratio, development time, mass, morphology, fecundity, and behavior. Our results suggest that negative effects of herbicides, clopyralid and fluazifop-p-butyl, and adjuvants, Agri-Dex® and Nu Film® IR, are limited. However, we detected weak effects of clopyralid, clopyralid with Agri-Dex®, fluazifop-p-butyl, and fluazifop-p-butyl with Agri-Dex® on larval and pupal development time and pupal mass. Any possible negative direct effects of herbicides on Oregon silverspots must be weighed against the positive indirect effects that herbicides are likely to have on the butterfly through improvements in habitat conditions. Our findings will inform managers who are selecting among available tools with which to restore native plant communities, while minimizing adverse effects on declining species, such as the Oregon silverspot.