Skip to main content
U.S. flag

An official website of the United States government

Environmental factors affecting survival of immature Ixodes scapularis and implications for geographical distribution of lyme disease: The climate/behavior hypothesis

January 13, 2017

Recent reports suggest that host-seeking nymphs in southern populations of Ixodes scapularis remain below the leaf litter surface, while northern nymphs seek hosts on leaves and twigs above the litter surface. This behavioral difference potentially results in decreased tick contact with humans in the south, and fewer cases of Lyme disease. We studied whether north-south differences in tick survival patterns might contribute to this phenomenon. Four month old larvae resulting from a cross between Wisconsin males and South Carolina females died faster under southern than under northern conditions in the lab, as has previously been reported for ticks from both northern and southern populations. However, newly-emerged larvae from Rhode Island parents did not differ consistently in mortality under northern and southern conditions, possibly because of their younger age. Survival is lower, and so the north-south survival difference might be greater in older ticks. Larval survival was positively related to larval size (as measured by scutal area), while survival was positively related to larval fat content in some, but not all, trials. The difference in larval survival under northern vs. southern conditions might simply result from faster metabolism under warmer southern conditions leading to shorter life spans. However, ticks consistently died faster under southern than under northern conditions in the laboratory when relative humidity was low (75%), but not under moderate (85%) or high (95%) RH. Therefore, mortality due to desiccation stress is greater under southern than under northern conditions. We hypothesize that mortality resulting from the greater desiccation stress under southern conditions acts as a selective pressure resulting in the evolution of host-seeking behavior in which immatures remain below the leaf litter surface in southern I. scapularis populations, so as to avoid the desiccating conditions at the surface. If this hypothesis is correct, it has implications for the effect of climate change on the future distribution of Lyme disease.

Publication Year 2017
Title Environmental factors affecting survival of immature Ixodes scapularis and implications for geographical distribution of lyme disease: The climate/behavior hypothesis
DOI 10.1371/journal.pone.0168723
Authors Howard S. Ginsberg, Marisa Albert, Lixis Acevedo, Megan C. Dyer, Isis M. Arsnoe, Jean I. Tsao, Thomas N. Mather, Roger A. LeBrun
Publication Type Article
Publication Subtype Journal Article
Series Title PLoS ONE
Index ID 70179725
Record Source USGS Publications Warehouse
USGS Organization Patuxent Wildlife Research Center