Laboratory Studies of Questing Behavior in Colonized Nymphal Amblyomma maculatum Ticks (Acari: Ixodidae).

Environmental factors affect host-seeking behavior in ticks. In this study, 80 nymphal Amblyomma maculatum Koch were released in an observation arena containing four different heights of broomsedge stems (Andropogon virginicus L.) anchored in sand. Observations were made over three days as to proportion of ticks questing, questing height, and stem height distribution This scenario was replicated three times with different cohorts of ticks (n = 80 per replicate) for each of three treatment combinations of temperature and humidity: High temperature/high humidity (HTHH), high temperature/low humidity (HTLH), and low temperature/high humidity (LTHH). A fourth treatment utilizing the same size cohort and number of replicates included Wind (HTHHW+/-) by alternating days of wind and no-wind conditions over four days. Mean questing height for ticks under HTHH, HTLH, and LTHH conditions ranged from 4.45 to 6.03 cm with ticks questing significantly higher in HTHH. A significantly lower proportion ticks quested in HTLH (8.64%) than HTHH (14.06%) and LTHH (15.33%). In HTHH and LTHH, a significantly higher proportion of ticks were observed questing on 5-cm stems. Wind significantly reduced average questing height, and when absent, ticks on 20- and 30-cm stems quested significantly higher. These data indicate that A. macuatum nymphs randomly select stems to quest upon and climb upward until environmental conditions are prohibitive/ideal. Conditions with reduced vapor pressure deficit (VPD) led to higher questing frequency and height. Relatively low questing heights observed correspond with size of preferred hosts and may explain infrequency of collection by dragcloth in the field.

Morphometric Analysis of Adult Dermacentor parumapertus Neumann (Acari: Ixodidae) From Various Locations Within its Geographical Range.

Dermacentor parumapertus Neumann (Acari: Ixodidae), a tick primarily associated with rabbits which occurs over much of the western United States, has a fairly large north-to-south distribution, being found from central Idaho southward into northern Mexico. This mostly obscure tick species has recently been the focus of attention due to the discovery of a unique strain of Rickettsia parkeri associated with it which appears closely related to a Rickettsia sp. found in the Atlantic rainforest of Brazil. Historically, a morphological variety of this species was reported in the literature based on significant variation in ornamentation of the tick throughout its range. This study examines several key morphological characters to determine if there are indeed more than one distinct population of this species throughout its range.

Field Observations of Questing and Dispersal by Colonized Nymphal Amblyomma maculatum Koch (Acari: Ixodidae).

: Almost nothing is known about the questing and dispersal behavior of immature Gulf Coast ticks (Amblyomma maculatum), a vector of both medical and veterinary concern. This experiment examined host-seeking (questing) and dispersal of marked, previously colonized, nymphal A. maculatum released in field plots in rural Oktibbeha County, Mississippi during 2015. A total of 500 (250 per replication) A. maculatum nymphs were painted and released in 5 plots (50 ticks each time). Observations were then made 5 times, approximately every 3 days, searching the plots for ticks from the release points outwards to 50 cm. Mean overall vertical questing height of ticks in Replication 1 in March (5.13 cm) was significantly higher than that of Replication 2 in April (2.57 cm) for a combined mean questing height of 3.58 cm. Ticks dispersed at a mean rate of 1.71 cm/day (Replication 1) and 0.98 cm/day (Replication 2), for an overall mean dispersal rate of 1.27 cm/day. When observation days where tick movement was impacted by adverse weather conditions were excluded, means between the replications were much closer. Only 38 of 2,500 possible total observations (1.5%) of the marked ticks were subsequently seen questing in this study, perhaps mirroring low questing rates of nymphal A. maculatum in nature. Additionally, 2 ticks were found in dense vegetation at the base of a plant. These data show that nymphs of this species disperse slowly, quest low to the ground, and can hide in very dense vegetation.

Evaluation of Human Attachment by Larval Amblyomma maculatum (Acari: Ixodidae).

The tick, Amblyomma maculatum Koch (Gulf Coast tick), has recently been shown to be an important disease vector of both medical and veterinary concern. Although much is known about the behavior and ecology of adults, little is known of the immatures. Larval feeding on humans has never been demonstrated (and thus, there are no collection records from humans). In this experiment, 10 larval A. maculatum, Amblyomma americanum (L.) (a positive control), and Dermacentor variabilis (Say) (a negative control), were applied to both forearms of 10 human volunteers (five male, five female). Ticks were placed in plastic caps and secured to skin with medical-grade adhesive tape, and volunteers remained sedentary during the experiment. After 15 min, caps were removed, and attachment was determined using fine-tipped forceps. Any A. maculatum that were attached were then removed and subsequently examined microscopically to verify identification. In total, 34 ticks attached to the subjects, including 11 A. maculatum (5.5%), 23 A. americanum (11.5%), and no D. variabilis. Amblyomma maculatum attached to six volunteers, and no apparent association between gender and attachment rate was noted. No skin lesions developed in the human volunteers bit by A. maculatum. This is the first report of larval A. maculatum attaching to humans, and is significant in that Rickettsia parkeri, a human pathogen vectored by this species, has recently been reported to be transmitted transovarially. If A. maculatum are infected as larvae, they could potentially transmit R. parkeri to people.