Dermacentor andersoni has been collected north of Jasper, Alberta, close to 54° N. and near 53° N. in British Columbia. Spread to the north and northwest is probably limited by low summer soil temperatures, which would act principally by slowing egg development, thus disrupting the seasonal cycle of the tick. To the southwest, mild winters may fail to release diapause at the correct time of year. Aspect and slope are important factors. Altitude spread of records is from 1000–7000 ft. The most generally applicable description of its distribution is the ecotone between western grassland and moister regions, including clearings and rocky outcrops m the montane and Columbia forests, and shrubby areas of the prairies. In British Columbia, a series of randomly selected transects indicated a strong association between the tick's presence and several species of shrubs growing without tree shade.Each bioclimatic zone tends to have a characteristic group of rodents as main hosts of the immature stages. The prairie and montane regions differ in the indigenous hosts available to the adult tick.East of 105° D. andersoni is replaced by D. variabilis, which is adapted to the more humid summers of the eastern deciduous forest zones, and differs considerably from D. andersoni in its phenology. There are no reliable records of indigenous D. variabilis north of 52° latitude.D. albipictus occurs from the east to the west coast. Because of the winter activity of its larvae, allowing the whole summer for egg development, it is able to penetrate much farther north than the other two species. There are two records close to 60° latitude.
Artificial tick foci or "rodentaria", infested with ovipositing females or larvae, have furnished new information on D. andersoni biology, and a means of mass production of adults for acaricide and other tests. Both a 1-year and a 2-year life cycle were observed, depending on the date the larvae emerged or were put out. Each year, adult ticks wandered near the soil surface in the fall but did not seek hosts or climb up to questing positions until spring. A tendency for the adult ticks to congregate southwards of the point of dropping of the engorged nymphs was discernible.In a large-scale rodentarium involving 24 runways, with four replicates of each of six species of rodents, by far the largest number of adult ticks was produced by Marmota flaviventris, but on a tick per unit weight of rodent basis, this species was low in the approximate order calculated.Adult ticks were ready to feed in mid-December in one trial, but they were inactive in the rodentarium because soil temperatures under the snow were usually about 0 °C, and activity does not begin until about 5 °C. The cycles observed in the rodentaria and the field indicate that both 1- and 2-year life cycles occur in southern British Columbia at an altitude of about 1000 ft. At higher altitudes and latitudes, a 3-year life cycle with overwintering larvae may occur. About 10% of the ticks marked in their first year of activity in 1964 were active the next spring.Female ticks from both 1-year and 2-year cycles were capable of paralyzing sheep.
Observations on the gradual distension and shrinkage of cattle tick larvae (Boophilus microplus (Canestrini)) confirmed that they can take up water from, or lose water to, the atmosphere under suitable conditions. Further evidence was obtained that partially desiccated larvae can drink when in contact with free water. Consideration of the relative humidities recorded over sward adjoining a creek, during a drought, suggested that larvae would be able to absorb moisture during the 9-hr period before dawn. Dew m-as also available to the larvae in drought time, and on most mornings when observations were made. In the laboratory, larvae in cultures supplied with water droplets lived longer than those in similar cultures not supplied with water. Larval clusters on artificial supports out of doors lived longer if protected by fabric shades. At intervals over 2 years, female ticks were placed in grassland near Rockhampton and at Yeppoon, Qld., under simulated natural conditions. The times of hatching and periods of survival of the larvae were observed. In contrast with the marked decrease in tick fertility which occurs in the winter in south Queensland, ticks put out throughout the winter at Rockhampton laid large numbers of fertile eggs. Very few larval progeny of ticks put out in summer survived 3 months after the date of placement of the parent female. Progeny of ticks put out in the winter persisted up to 54 months after the date of placement of the parent. A graph of the 'pre-hatch' (pre-oviposition plus developmental) periods against screen temperatures followed the trend expected from laboratory data, but the difference between actual and computed hatching dates was large in some cases. Actual hatching date was usually later than computed hatching date, both for ticks in the soil and for ticks in humidified containers in a meteorological screen. The comparatively short survival periods of larvae in the central Queensland summer indicated the practicability of controlling the cattle tick by temporarily destocking pastures.
A small herd of cattle infested with the cattle tick, Boophilus microplus (Canestrini) was kept in a previously unstocked paddock for 11 months without treatment for tick infestation. Frequent examinations showed that widely differing numbers of ticks developed on the cattle. The "tick resistance" of one animal, which showed no adult ticks during the summer months, could only be accounted for by mortality of the larvae and nymphs on the animal, since as many larvae were seen on selected small areas of this animal as on some animals carrying many adult ticks. The animals grazed together and thus would encounter similar numbers of tick larvae. The degree of susceptibility to adult tick infestation showed negligible correlation with skin thickness measurements and was not related to coat length. Larvae reappeared on the cattle 6 weeks after the first stocking of the paddock in March. The animals became almost free of ticks for 2 weeks in August. Although larvae were most numerous in November-December, they gave rise to fewer adults than the earlier wave of larvae in September- October. Some of the cattle suffered from "tick-worry'' in October, but thereafter their condition improved without treatment.
In larval cattle ticks the main sense organs which have been recognized are the eyes, Haller's organs, and the palpal organs; the four pairs of sensilla sagittiformia may also have a sensory function. Larvae were allowed to ascend supports simulating grass stalks and were tested for response to vibration, air currents, interrupted illumination, warm and moist objects, and odours from skin secretions of man and cattle. The strongest questing response was to the odours. Larvae which had been exposed to low humidities collected around and imbibed from drops of water. The main stimulus governing ascent of the grass blades appeared to be positive phototaxis to moderate light intensities. Larvae sheltered from direct sunlight. Larvae in the field were found to be more exposed in the early morning, often being at the tops of grass stalks. Measurements of light, air temperature, and humidity indicated that light intensity might govern this movement. This suggests that larval sampling in the pasture should take place in the first half of the morning. In a single series of observations, larvae which had hatched at the base of straws were observed to ascend them in the late afternoon. In a few experiments isolated larvae ascended artificial supports above the reach of a bovine host but groups were always found at heights within reach.
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