Factors Affecting Host-plant Quality and Nectar Use for the Karner Blue Butterfly: Implications for Oak Savanna Restoration

Abstract

In the Midwestern United States, more than 99.99% of pre-settlement oak (Quercus) savanna has been lost due to agriculture and fire suppression. Thus, the restoration of this ecosystem is imperative to secure the biodiversity, which depends on oak savanna. In this study, we characterized factors affecting the host-plant quality and nectar use of the endangered Karner blue butterfly (Lycaeides melissa samuelis Nabokov) in Ohio. Past research has shown butterfly abundance to be correlated with host-plant quantity, habitat area, and nectar plant abundance. However, there is growing recognition that host-plant quality is important at small spatial scales. We measured host-plant quality by quantifying leaf nitrogen content for the first larval brood and a PCA analysis of nitrogen and water content for the second larval brood. Additionally, observations quantified adult female foraging rates. Our results for the first brood larval stage found no significant difference in leaf nitrogen between burned, mowed, and unmanaged treatments. We used Akaike's Information Criteria (AIC) to determine that host-plant quality for the second brood was primarily explained by herbaceous vegetation density followed by canopy cover and aspect. Greater herbaceous vegetation density, greater canopy cover, and flat/north aspects were associated with higher quality host-plants. Lower host-plant nitrogen for the second brood was accompanied by a greater adult foraging rate. Management of Karner blue habitats should include restoring areas with a compatible herbaceous structure and increasing historically abundant forbs, which provide nectar to second brood Karner blues. This ecosystem-based management should positively impact many species in this rare oak savanna community.