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Title: Comparative off-host survival of larval Rocky Mountain wood ticks (dermacentor andersoni) collected from distinct field populations

Author
item OWEN, JEB - Washington State University
item VANDER VLIET, ANN - Washington State University
item Scoles, Glen

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2013
Publication Date: 3/25/2014
Citation: Owen, J.P., Vander Vliet, A., Scoles, G.A. 2014. Comparative off-host survival of larval Rocky Mountain wood ticks (dermacentor andersoni) collected from distinct field populations. Parasites & Vectors. DOI:10.1111/mve.12049.

Interpretive Summary: The Rocky Mountain Wood Tick (RMWT; Dermacentor andersoni Stiles) is found throughout the western United States and transmits pathogens of importance to human and animal health. Variation in distribution and seasonal activity of RMWTs suggest that climate affects the population dynamics of the tick. It is unknown if responses to climate variation differ across the tick's geographic range. The objective of this study was to compare off-host survival of larval RMWTs collected from isolated field populations, to better predict how weather and landscape may influence tick distributions and population dynamics. We collected RMWTs from field sites in Montana and Oregon states (USA). We tracked weekly survival of tick larvae under four combinations of relative humidity (RH) (75% and 98%) and temperature (26°C and 32°C) that reflected the range of conditions observed in the source habitats during spring-summer. D. andersoni ticks from two field populations had similar patterns of survival under different ambient temperatures. Though one tick population (Oregon) was unaffected by a decrease in relative humidity, the other population (Montana) had lower survival when RH was reduced. These data support field observations that RMWT distributions are shaped by ambient conditions and suggest that the tolerance limits of ticks differ among populations.

Technical Abstract: Background: The Rocky Mountain Wood Tick (RMWT; Dermacentor andersoni Stiles) is found throughout the western United States and transmits pathogens of importance to human and animal health. Variation in distribution and seasonal activity of RMWTs suggest that climate affects the population dynamics of the tick. It is unknown if responses to climate variation differ across the tick's geographic range. The objective of this study was to compare off-host survival of larval RMWTs collected from isolated field populations, to better predict how weather and landscape may influence tick distributions and population dynamics. Findings: We collected RMWTs from field sites in Montana and Oregon states (USA). We tracked weekly survival of tick larvae under four combinations of relative humidity (RH) (75% and 98%) and temperature (26°C and 32°C) that reflected the range of conditions observed in the source habitats during spring-summer. For both populations, larval survival decreased at the higher ambient temperature (50% mortality 1-2 weeks earlier). A change in RH did not affect the survival of larvae from Oregon. In contrast, the survival of larvae from Montana decreased at the lower RH (50% mortality 1 week earlier). Conclusions: D. andersoni ticks from two field populations had similar patterns of survival under different ambient temperatures. Though one tick population (Oregon) was unaffected by a decrease in relative humidity, the other population (Montana) had lower survival when RH was reduced. These data support field observations that RMWT distributions are shaped by ambient conditions and suggest that the tolerance limits of ticks differ among populations.