Graduate Thesis Or Dissertation
 

A study of ticks (Acarina: Ixodidae) and chiggers (Trombiculidae) from two areas in western Oregon

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  • A study of the host range and distribution of ticks and chiggers (Acari) was undertaken in two contrasting forested areas of western Oregon. Acarines were sampled from host mammals which were trapped along line transects laid out in both areas, each consisting of 18 stations 50 feet apart. Hosts were captured alive and the ticks and chiggers removed. Hosts were marked and then released to make recapture possible. The deer mouse was the most common host recaptured in either sampling area. Ixodes angustus Neumann proved to be the most common tick in the coastal sampling site (Neptune State Park). Ixodes soricis Gregson was less abundant in this area and I. pacificus Cooley and Kohls was absent. Immature stages of I. pacificus were found in moderate numbers in the valley sampling site (William L. Finley National Wildlife Refuge) in the summer and fall. The chiggers Euschbngastia oregonensis (Ewing), Comatacarus americana (Ewing), and Chatia setosa Brennan were most common in the Neptune study area, while Neotrombicula cavicola Ewing was most abundant in the William L. Finley study area. Good evidence is supplied by host records in this study that I. angustus most commonly infests nest building mammals. Lack of records from larger animals or from the "flag" illustrates its absence on vegetation and soil litter, or duff. Ixodes soricis was found on shrews and the shrew-mole in this study. None was collected from other moles although heavy parasitization by immatures of I. angustus on these hosts was recorded. I. pacificus is the only central western Oregon species of this genus that climbs vegetation or that feeds on larger animals including man. Immatures of I. pacificus were collected from small mammal and lizard hosts in the Finley study area in summer and fall. Mean number of immature ticks per host was higher for lizards than for small mammals indicating the importance of these hosts for the maintenance of tick populations. The chigger C. americana was found mostly on shrews and moles in both sampling areas. E. oregonensis commonly attached around the eyelids on deer mice, but on other parts of the body on shrews. N. harperi and N. cavicola were not found on deer mice in this study and most of the chiggers were found in the ear canals of voles or chipmunks. A negative correlation factor was used to measure the degree of compatibility between different parasites on a single host. The negative binomial distribution adequately described the pattern of distribution of L angustus and E. oregonensis in both study areas. The species of trombiculids identified during the course of this study may be segregated into two ecological groups: (1) soil litter forms, and (2) burrow-inhabiting forms. Ch. setosa, C. americana, and E. oregonensis probably occur in burrows while N. harperi and N. cavicola inhabit soil litter. N. harperi was found only in summer months and is probably affected by phenology.
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