Ticks are obligate blood-sucking arachnid ectoparasites from the order Acarina, and many are notorious as vectors of a wide variety of zoonotic pathogens. However, the systematics of ticks in several genera is still controversial. The mitochondrial genome (mt-genome) has been widely used in arthropod phylogeny, molecular evolution and population genetics. With the development of sequencing technologies, an increasing number of tick mt-genomes have been sequenced and annotated. To date, 63 complete tick mt-genomes are available in the NCBI database, and these genomes have become an increasingly important genetic resource and source of molecular markers in phylogenetic studies of ticks in recent years. The present review summarizes all available complete mt-genomes of ticks in the NCBI database and analyses their characteristics, including structure, base composition and gene arrangement. Furthermore, a phylogenetic tree was constructed using mitochondrial protein-coding genes (PCGs) and ribosomal RNA (rRNA) genes from ticks. The results will provide important clues for deciphering new tick mt-genomes and establish a foundation for subsequent taxonomic research.

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Background: The tick Haemaphysalis longicornis is well known as vector of several zoonotic pathogens responsible for various clinical conditions, increasingly threatens the veterinary and public health. It is mainly distributed in East Asia, New Zealand, Australia, and several Pacific islands, and has been expanded rapidly in United States since its first founding on a nonimported domestic sheep in New Jersey. Glutathione S-transferases (GSTs) are phase II detoxification enzymes, which function via combining with pesticidal molecules and catalyzing the conjugation of molecules by thiol of glutathione, so as to protect tissues from oxidative stress damage. In the tick H. longicornis, glutathione S-transferases (HlGST and HlGST2) have been previously identified. However, the relationship between the expression of glutathione S-transferases and the essential oil treatment in ticks remains unexplored. Hence, in the present study, the expression profiles of HlGST and HlGST2 mRNAs were evaluated in H. longicornis after exposure to Cymbopogon citratus essential oil. Results: At 24 h post-exposure of H. longicornis to different sublethal concentrations of C. citratus essential oil, ANOVA results revealed significant difference (F2,6 = 55.94, P = 0.0001) in the expression of HlGST. Tukey’s test showed that HlGST was significantly induced after treatment with 1% C. citratus essential oil (P = 0.0002); whereas no significant difference (P = 0.3551) was detected after treated by 2% C. citratus essential oil. No significant difference (F2,6 = 0.8990, P = 0.4555) in the expression of HlGST2 between the treatment and the control group of 50% ethanol. Nevertheless, the under-expression of HlGST2 in the treatment groups versus the untreated control group was not significant (F3,8 = 2.643, P = 0.1208). Conclusion: The results implied that GST mRNA is a potential molecular target for C. citratus essential oil in H. longicornis. Further understanding of the underlying mechanisms of the GST at the molecular level could contribute to develop effective control measures for ticks and tick-borne diseases.

The tick Haemaphysalis longicornis is widely distributed in eastern Asia, New Zealand and Australia, and is well-known as a vector of multiple zoonotic pathogens. This species exhibits two reproductive strategies, bisexual and obligate parthenogenetic reproduction. Hence, in the current study, the complete mitochondrial genomes of the bisexual and parthenogenetic populations were assembled and analyzed, and the expression of the mitochondrial protein-coding genes was evaluated and compared between the two reproductive populations. The results indicated that the length of the mitochondrial genomes of the two reproductive populations is 14,694 and 14,693 bp in the bisexual and parthenogenetic populations, respectively. The AT content in the mitochondrial genome of the bisexual and obligate parthenogenetic population reached 77.22 and 77.34%, respectively. The phylogenetic tree was constructed combining 13 protein-coding genes, which showed that the genetic distance between the bisexual and parthenogenetic populations was less than that between the subspecies. The expression of the mitochondrial protein-coding genes was quantitatively analyzed at different feeding status for the bisexual and parthenogenetic populations, and the results showed significant differences in the expression patterns of these genes, suggesting that they might trigger specific energy utilization mechanisms due to their different reproductive strategies and environmental pressures.