Long-term trends in Persea palustris and Lauraceae-dependent butterfly species in central Florida before and after the introduction of laurel wilt disease

Abstract

Laurel wilt disease (LWD) is a highly virulent disease vectored by an invasive beetle. It was first observed in South Carolina in 2003, and it is now found in all Florida counties and nine southeastern US states. This disease causes extensive mortality of Lauraceae plants, an ecologically and economically important group. Many arthropods are associated with Lauraceae species, including palamedes (Papilio palamedes (Drury)) and spicebush (Papilio troilus (L.)) swallowtail butterflies, which host on swamp bay (Persea palustris) and redbay (Persea borbonia). It is thought that P. palamedes are at greatest risk from LWD. Limited information exists on the impacts on these butterflies after LWD becomes established. Therefore, we use a unique long-term tree and butterfly dataset in central Florida that spanned the introduction of LWD. We found that over two decades, swamp bay declined 90% in abundance. Interestingly, the majority (70%) of the swamp bays’ decline preceded the introduction of LWD. We suspect that a 5 year severe drought was the primary cause of mortality, since there was a 45% reduction in overall tree abundances. Despite these large reductions, a small number of swamp bay trees persisted, and others sprouted from basal roots. Butterfly monitoring began after 70% of the swamp bays had died. We found that, even though there was extensive loss of swamp bays, P. palamedes and P. troilus populations were relatively stable, and potentially were increasing. However, after LWD was confirmed in this area, these butterflies declined slightly. We also found that the reduction was slightly greater in P. palamedes than P. troilus. P. palamedes are more dependent on swamp bay whereas P. troilus are more adaptable at host-switching, perhaps to a Lauraceae tree Cinnamomum camphora (L.) J. Pesl. (Camphortree), which is common in our area and does not appear to be locally affected by LWD. Thus, while we found that swamp bay declined dramatically, dependent butterfly populations declined far less dramatically. Butterflies may be surviving because of host-switching, or because the remaining trees provide enough resources. Future research should focus on the persistence of these species, especially as this disease continues to spread throughout the southeastern US.