Non-native, invasive shrubs in eastern deciduous forests may affect tick-borne disease risk by increasing tick abundance and/or altering pathogen prevalence. At a fine scale, the dense growth form of these shrubs can create a favorable microclimate for tick survival or aggregate tick hosts. Whether these shrubs also confer changes to habitat characteristics that could influence tick-borne disease risk at a broader spatial scale has remained largely unexplored. Here, we investigated the relationship between multiflora rose (Rosa multiflora), an exotic invasive understory shrub, and blacklegged tick (Ixodes scapularis) abundance and pathogen prevalence in urban forest fragments in and around Newark, DE, USA. Using multiplex real-time PCR assays, we quantified the prevalence of four zoonotic, tick-borne pathogens. We then used Bayesian logistic regression and WAIC model selection to understand how vegetation, habitat, and landscape features of urban forests relate to the prevalence of B. burgdorferi(the causative agent of Lyme disease) among blacklegged ticks.
Results/Conclusions
Within rose-invaded forests, we trapped about 2.5 times more blacklegged tick nymphs under rose compared to paired points away from rose (t19= 2.37, P = 0.03). Yet, at the broader spatial scale, we trapped more than 3 times as many ticks in rose-free forest fragments compared to rose-invaded forest fragments (F1,53= 30.27, P < 0.01). Among 258 nymphs tested, we detected Borrelia burgdorferi in 11.2% of ticks. Ticks collected from rose-invaded forests had greater B. burgdorferi infection rates (mean = 15.9%) than ticks collected from uninvaded forests (mean = 7.9%). Overall, B. burgdorferi prevalence among ticks was positively related to habitat features (e.g. coarse woody debris and total understory cover) favorable for competent reservoir host species. Understory structure provided by multiflora rose appears to aggregate ticks and reservoir hosts, increasing opportunities for pathogen transmission. However, when we consider pathogen prevalence among nymphs in context with relative abundance of questing nymphs, invasive plants do not necessarily increase Lyme disease risk at a landscape scale. Although pathogen prevalence was greater among ticks in rose-invaded forests, the probability of encountering an infected tick remained greater in uninvaded forest fragments that had relatively greater questing tick abundance.