Invasive exotic species pose a significant threat to native diversity via well studied direct effects, as well as often overlooked indirect pathways. Amur honeysuckle (Lonicera maackii) (hereafter ‘Lonicera’) is a highly aggressive and successful shade-tolerant invasive woody shrub that directly affects native plant diversity and abundance by overshadowing natives with its dense canopy and through allelopathic effects. One indirect effect of this invasion that has not been intensively explored is the potential for invasive species to alter the abundance and composition of vertebrate hosts of Ixodid ticks. As recent evidence suggests that Lonicera species may cause a local increase in the abundance of mammalian hosts of the lone star tick (Amblyomma americanum) (hereafter ‘tick’), we hypothesized that Lonicera could indirectly increase human risk of exposure to pathogens transmitted by ticks via the indirect pathways of increased abundance of important tick hosts and reservoir species. We established a large-scale experiment at the August A. Busch Memorial Conservation Area near St. Louis,
Results/Conclusions
Using CO2-baited traps, we found significantly higher densities of both nymphal and adult life stages of ticks in plots where Lonicera was left intact versus plots where it had been removed. Using a combination of polymerase chain reaction and reverse line blot hybridization, we further found that where Lonicera was left intact, there was a significantly higher prevalence of an emerging tick-borne pathogen, Ehrlichia chaffeensis. These results indicate that in plots where Lonicera is present there is an 8-fold increase in the density of infected nymphs, our best estimate of human risk of exposure to this tick-borne pathogen. Overall, our results suggest an important, but previously undetected, cost of a noxious invasive shrub on native ecosystems, cascading from changes in community structure to increases in human health risk.
