Association between the palamedes swallowtail (Papilio palamedes) and orange-fringed orchid (Platanthera ciliaris) on the northern Gulf Coast: potential consequences of laurel wilt disease

Disturbances by invasive alien insects reduce the dominance of native species, imperil herbivores that depend on the impacted species, and threaten ecosystem services provided by the adult stages of these herbivores. Laurel wilt disease (LWD) has spread via an exotic ambrosia beetle (Xyleborus glabratus) throughout many Coastal Plain habitats. Most incidences of LWD-induced mortality occur in redbay (Persea borbonia), an abundant sub-canopy species and primary larval host of the palamedes swallowtail butterfly (Papilio palamedes). Decline of P. palamedes due to widespread LWD-induced mortality of redbay may negatively affect the fitness of plants that have specialized associations with P. palamedes. The orange-fringed orchid (Platanthera ciliaris) could be at risk as its flowers have especially long nectar spurs that attract the longest-tongued pollinators (e.g. P. palamedes). We quantified pollinator visitation and fruit set in a population of P. ciliaris at Grand Bay National Estuarine Research Reserve in coastal Mississippi. We also measured length of flower nectar spurs and pollinator proboscises. Over three days of observation, mean number of pollinator visits per plant hr^-1 was 0.52 ± 0.17. We recorded 44 visits by P. palamedes and 4 by Phoebis sennae (giant sulfur). Average length of their proboscises did not differ from each other or the length of P. ciliaris nectar spurs. Average fruit set per plant was 55%, significantly greater than bagged specimens. Our results suggest that P. palamedes is the primary pollinator of P. ciliaris and that its anticipated LWD-induced decline may reduce plant fitness unless pollinator services by P. sennae increase.