Cascade effect of laurel wilt disease on the palamedes swallowtail butterfly (Papilio palamedes) in the southeastern United States

Laurel wilt disease (LWD) has caused widespread mortality of redbay (Persea borbonia (L.) Spreng.), a common understory tree of southeastern U.S. maritime forests. Redbay is the primary larval food source for the palamedes swallowtail butterfly (Papilio palamedes Drury) and LWD-induced morality of redbay may have a direct effect on palamedes abundance. To determine if the removal of redbay has a direct effect on the abundance of the palamedes swallowtail, ~400 meter (1/4 mile) “Pollard transects” were walked and butterflies within 15 meters on each side of the observer were tallied. Three transects were walked per stand type (i.e. infected and uninfected stands). Infected stands are defined where LWD has been present ³3 years. To date, transects have been performed in Mississippi (3 years) and North Carolina (2 years) with data collection continuing for a minimum of 3 years in each state. Weather conditions (wind speed, temperature, % cloud cover, and humidity) were recorded at the beginning of each transect. Preliminary results from Mississippi indicate palamedes abundance has decreased in infected stands, and in North Carolina palamedes abundance has also decreased in infected stands. These results suggest that LWD-induced mortality of redbay is leading to a decrease in palamedes abundance and extinction or long term decline of redbay may lead to the loss of the palamedes swallowtail throughout much of its range. Other multi-trophic cascade effects may also become evident as LWD continues to alter the ecosystem. These results indicate the need for focused conservation efforts aimed at protecting crucial palamedes habitat and planting and management of refugia. These results also indicate the need to monitor the removal of sassafras, another laurel species vulnerable to LWD, and its possible effect on spicebush swallowtail (Papilio troilus L.) abundance.