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Title: Factors affecting larval tick feeding success: host, density and time

item JONES, CAMI - Washington State University
item BRUNNER, JESSE - Washington State University
item Scoles, Glen
item OWEN, JEB - Washington State University

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2015
Publication Date: 6/24/2015
Citation: Jones, C.R., Brunner, J.L., Scoles, G.A., Owen, J.P. 2015. Factors affecting larval tick feeding success: host, density and time. Parasites & Vectors. doi: 10.1186/s13071-015-0955-6.

Interpretive Summary: Transmission of vector-borne pathogens is strongly affected by arthropod abundance; greater vector densities increase biting rate, which increase the risk of transmission. In addition, for most blood-feeding arthropods the blood meal is necessary to support development and reproduction. This intimately links blood-feeding success to tick population dynamics and thus pathogen transmission dynamics. Many factors can influence the feeding success of ticks and other ectoparasites, yet it remains unclear whether host and tick characteristics (prior exposure to ticks, age of the host and tick, density of the tick) are equally important, or if they affect blood feeding success. Here we ask how blood-feeding success changes with the age and prior exposure of the host, and with the tick’s age and density. We used a naturally occurring host-ectoparasite association between the Rocky Mountain wood tick (RMWT) and deer mice. Our data reveal that tick density, prior infestation of the host, host age and tick age will each affect the blood feeding success of larval RMWTs. Ecologically these data suggest that the biotic factors driving feeding success of RMWT larvae could be (i) the ratio of naïve versus tick-infested hosts in a population, (ii) the density of ticks in the environment, (iii) the ratio of young versus old hosts and (iv) the ages of the larvae at first encounter with a host. Small numbers of larvae that get on an older, naïve host earlier in the season will have a better chance of surviving to the next life-stage. Variation in these relationships may cause changes in tick population dynamics and the probability of pathogen transmission. These data add to the much needed information on biology and ecology of tick larvae, which will improve modeling of tick population dynamics.

Technical Abstract: Background: Ectoparasites rely on blood feeding to sustain activity, support development and produce offspring. Blood feeding is also a route for transmission of diverse vector-borne pathogens. The likelihood of successfully feeding is thus an important aspect of ectoparasite population dynamics and pathogen transmission. Factors that affect blood feeding include ectoparasite density, host defenses and ages of the host and ectoparasites. How these factors interact to affect feeding success is not well understood. Methods: We monitored blood-feeding success of larval Rocky Mountain wood ticks (RMWTs; Dermacentor andersoni) on deer mice (Peromyscus maniculatus) in several experiments to determine how tick density, host defense, and ages of mice and ticks interact to influence feeding success. In the first experiment, tick-naive deer mice were infested with one of several densities of RMWT larvae, while a second cohort of mice were infested with 50 larvae each. Two weeks after ticks dropped off, mice in the first cohort were re-exposed to 50 larvae each and mice in the second cohort were re-exposed to varying densities of larvae. In the second experiment mice of different ages (45-374 days old) were exposed to 50 larvae each. Two weeks later mice were re-exposed to 50 larvae each. We combined data from these and several similar experiments to test the generality of the patterns we observed. Lastly, we tested whether tick feeding success was consistent on individual mice that were challenged on four occasions. Results: Mice acquired resistance such that feeding success declined dramatically from the first to the second infestations. Feeding success also declined with tick density and tick age. Mice, however, became more permissive with age. The sizes of these effects were similar and additive. Surprisingly, the relative resistance or permissiveness of an individual mouse changed among infestations. Conclusions: We predict that larval blood feeding success, and thus development to the nymph stage, will fluctuate due to variation in tick age and density, as well as the age and history of the host. Incorporating these biotic factors into modeling of tick population dynamics may improve predictions of tick-borne pathogen transmission.