A comparative evaluation of northern and southern Ixodes scapularis questing height and hiding behavior in the USA

Authors: TIETJEN, MACKENZIE - Texas A&M University; ESTEVE-GASENT, MARIA - Texas A&M University; Li, Andrew; MEDINA, RAUL - Texas A&M University

Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2020
Publication Date: 8/10/2020
Citation: Tietjen, M., Esteve-Gasent, M.D., Li, A.Y., Medina, R.F. 2020. A comparative evaluation of northern and southern Ixodes scapularis questing height and hiding behavior in the USA. Parasitology. https://doi.org/10.1017/S003118202000147X.
DOI: https://doi.org/10.1017/S003118202000147X

Interpretive Summary: Lyme disease is the most prevalent vector borne illness in the United States. The US Centers for Disease Control and Prevention (CDC) estimated over 300,000 human cases occur annually in the US. Lyme disease is caused by a spirochete bacterium which is vectored by the blacklegged tick (or deer tick). Over 90 % of Lyme disease cases being reported to the CDC are from 14 northeastern and northcentral states. Fewer cases are reported in the southeastern and southwestern states although both the pathogen and tick vectors are present in the south. Reasons for this geographic difference in Lyme disease prevalence are not fully understood. USDA ARS scientists joined force with researchers at Texas A&M University to investigate differences in questing behavior among ticks collected from Maryland and Texas. The study revealed nymphs from Texas quest at significantly lower heights compared to nymphs from Maryland, while adults from both states quest at a similar height. The results indicate immature stages of the deer tick may feed on different hosts in the south. The unique questing behavior of nymphs in the south may explain reduced risk for tick bite and Lyme disease in the region. The results obtained from this study are of interest to tick biologists and researchers who work in the field of Lyme disease ecology, tick control, and tick repellent development.

Technical Abstract: Ticks display a distinct type of host-seeking behavior called questing. It has been proposed that the questing behavior of Ixodes scapularis explains the geographic variation in Lyme disease (LD) risk in the eastern US as the northern and southern populations have been shown to exhibit different questing frequencies. The height at which questing occurs is variable and has been correlated with preferred host height in several tick species. This study aimed to characterize the height at which questing occurs in the two populations of I. scapularis. Ticks were collected from a northern state (i.e. Maryland) and a southern state (i.e. Texas) and behavioral bioassays were conducted in the laboratory. We report that nymphs from Texas are questing at lower heights compared to nymphs from Maryland. The mean questing height was 3.7 cm (± 2.5) for Texas nymphs which was significantly lower than Maryland nymphs with a mean of 21.0 cm (± 17.5). In addition, we report a behavior that hasn't been previously reported which we call 'hiding behavior' which interestingly, only Texas nymphs exhibited. These results may reflect the different composition and abundance of hosts between these two geographical areas as the southern US has a more diverse assemblage of host species with shorter heights including a higher abundance of lizards. In contrast, there was no significant difference in questing height between Maryland adults (20.2 cm ± 20.3) and Texas adults (30.5 cm ± 22.2) which was to be expected since adults are feeding on white-tailed deer in both locations. If all southern I. scapularis nymphs are questing at lower heights this might make them less likely to come into contact with humans and this may be contributing to the geographical difference in LD prevalence.