Local abundance of Ixodes scapularis in forests: Effects of environmental moisture,vegetation characteristics,and host abundance |
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| Institution: | 1. Institute for Circumpolar Health Studies, University of Alaska, Anchorage, 3211 Providence Drive, Anchorage, AK 99508 USA;2. Hopland Research & Extension Center, University of California Division of Agriculture and Natural Resources, 4070 University Road, Hopland, CA 95449 USA;3. University of Colorado Boulder, 3100 Marine Street, Boulder, CO 80309 USA;4. Department of Environmental Science, Policy and Management, University of California, Berkeley, 130 Hilgard Way, Berkeley, CA 95449 USA;5. Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Diseases, Centers for Disease Control and Prevention, 3156 Rampart Road, Fort Collins, CO 80526 USA;6. Vector-Borne Disease Section, California Department of Public Health, Richmond, CA USA;7. University of California Division of Agriculture and Natural Resources, University of California, Berkeley, 130 Hilgard Way, Berkeley, CA 95449 USA;1. Division of Vector-Borne Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, CO 80521, USA;2. Comparative Medicine and Integrative Biology, Michigan State University, East Lansing, MI 48824, USA;3. Michigan Department of Agriculture and Rural Development, Lansing, MI 48933, USA;4. Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824, USA;5. Vectorborne Diseases Unit, Minnesota Department of Health, St. Paul, MN 55164, USA;6. Department of Entomology, University of Wisconsin-Madison, Madison, WI 53706, USA;7. Department of Biology, University of Wisconsin-Stevens Point, Stevens Point, WI 54481, USA |
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| Abstract: | Ixodes scapularis is the primary vector of Lyme disease spirochetes in eastern and central North America, and local densities of this tick can affect human disease risk. We sampled larvae and nymphs from sites in Massachusetts and Wisconsin, USA, using flag/drag devices and by collecting ticks from hosts, and measured environmental variables to evaluate the environmental factors that affect local distribution and abundance of I. scapularis. Our sites were all forested areas with known I. scapularis populations. Environmental variables included those associated with weather (e.g., temperature and relative humidity), vegetation characteristics (at canopy, shrub, and ground levels), and host abundance (small and medium-sized mammals and reptiles). The numbers of larvae on animals at a given site and season showed a logarithmic relationship to the numbers in flag/drag samples, suggesting limitation in the numbers on host animals. The numbers of nymphs on animals showed no relationship to the numbers in flag/drag samples. These results suggest that only a small proportion of larvae and nymphs found hosts because in neither stage did the numbers of host-seeking ticks decline with increased numbers on hosts. Canopy cover was predictive of larval and nymphal numbers in flag/drag samples, but not of numbers on hosts. Numbers of small and medium-sized mammal hosts the previous year were generally not predictive of the current year’s tick numbers, except that mouse abundance predicted log numbers of nymphs on all hosts the following year. Some measures of larval abundance were predictive of nymphal numbers the following year. The mean number of larvae per mouse was well predicted by measures of overall larval abundance (based on flag/drag samples and samples from all hosts), and some environmental factors contributed significantly to the model. In contrast, the mean numbers of nymphs per mouse were not well predicted by environmental variables, only by overall nymphal abundance on hosts. Therefore, larvae respond differently than nymphs to environmental factors. Furthermore, flag/drag samples provide different information about nymphal numbers than do samples from hosts. Flag/drag samples can provide information about human risk of acquiring nymph-borne pathogens because they provide information on the densities of ticks that might encounter humans, but to understand the epizootiology of tick-borne agents both flag/drag and host infestation data are needed. |
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| Keywords: | Abundance Distribution Habitat Canopy cover Phenology |
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