The Gulf Coast tick: a review of the life history, ecology, distribution, and emergence as an arthropod of medical and veterinary importance.

The Gulf Coast tick, Amblyomma maculatum Koch (Acari: Ixodidae), is a unique univoltine ectoparasite of seven vertebrate host classes in the Western Hemisphere that is increasingly recognized as a pest of livestock and wildlife, a vector of pathogens to humans and canines, and a putative vector of Ehrlichia ruminantium, the causal agent of heartwater, a fatal foreign animal disease of ruminants resident in the Caribbean. This review assembles current and historical literature encompassing the biology, ecology, and zoogeography of this tick and provides new assessments of changes in cyclical population distribution, habitat associations, host utilization, seasonal phenology, and life history. These assessments are pertinent to the emergence of A. maculatum as a vector of veterinary and medical importance, and its pest management on livestock and other animals.

Genetic variation in 12S and 16S mitochondrial rDNA genes of four geographically isolated populations of Gulf Coast ticks (Acari: Ixodidae).

Single-strand conformation polymorphism (SSCP) analysis was examined in a 303-bp region of the 16S and 12S mitochondrial rDNA genes to study haplotype frequencies among populations of Gulf Coast ticks collected from Refugio Co., TX, Payne Co., OK, and two sites in Osage Co., KS. Seven haplotypes were identified from the 16S rDNA gene fragment, whereas only two haplotypes were detected from the 12S fragment. Only the results from the 16S rDNA fragment are discussed. Haplotype diversity was greatest in Kansas (site 1), where three of the four haplotypes detected were unique to this site. All Gulf Coast tick populations shared the fourth haplotype. Two haplotypes were determined for Texas and Oklahoma populations, one of which appeared only in Texas, whereas the other was shared. Nei's haplotype diversity (h) indicated that the Texas population was relatively homogeneous (15%), whereas the remaining populations were heterogeneous (42-59%), although the Bonferroni confidence interval found no significant differences (P < 0.05). Nucleotide sequencing of the seven haplotypes and subsequent phylogenetic analysis using neighbor joining showed a monophyletic relationship among these haplotypes. One haplotype, shared by both Oklahoma and Kansas (site 2), was basal to the remaining haplotypes and formed a distinct clade. Two haplotypes, both from Kansas (site 1), formed a unique clade, whereas the remaining four haplotypes were unresolved polytomies.

Mating success of two geographically distinct populations of Gulf Coast ticks, Amblyomma maculatum Koch.

Gulf Coast ticks collected from Refugio Co., TX and Osage Co., KS are reproductively compatible despite differences in genetic haplotypes, geographic separation and seasonal phenologies. Two heifers per mating combination (TX males x TX females, KS males x KS females, TX males x KS females, KS males x TX females) were each infested with 360 pairs of Gulf Coast ticks. Only mean pre-oviposition and mean egg conversion efficiency index for the Texas male-Kansas female mating were significantly different (p<0.05) from other mating treatments. These females began oviposition 1-day later and used 4% less body mass toward egg production when compared to site-specific matings. However, the overall trend in reproductive performance of reciprocal tick matings was slightly lower than that of site-specific matings. There appear to be no pre-zygotic barriers to mating among Gulf Coast ticks from these Texas and Kansas populations.

Feeding predilection of Gulf Coast tick, Amblyomma maculatum Koch, nymphs on cattle.

Gulf Coast tick nymphs successfully attached and fed on cattle after being freely released. Six Hereford heifers were each infested with approximately 2000 Gulf Coast tick nymphs, three with a strain originating from Refugio Co., TX, and three with ticks from Osage Co., KS by free release on the head and legs to simulate field acquisition of questing nymphs. Two re-infestations were conducted, the first at 7 days and the second at 28 days. Nymph dispersal was estimated by daily inspection of 22 body areas and removal of engorging ticks from the third to the fifth days post-infestation. Total recovery of engorging Texas nymphs was 3.0, 10.2, and 0% and Kansas nymphs was 21.5, 3.3, and 0% for infestations one, two and three, respectively. Immunological resistance to tick infestation expressed as cellular hypersensitivity was evident against Kansas nymphs in the second infestation and against both tick strains in the third infestation. Ticks removed from the withers, midline, and tail-head areas accounted for 68% of the total nymphs recovered in the first two infestations. Within these areas, nymphs were observed to aggregate in small spots where the hair was less dense or naturally parted and the remainder were found scattered in dense hair.