Amblyomma maculatum, Gulf Coast tick, male. Click on image to enlarge.

Amblyomma maculatum,
Gulf Coast tick, female.
Click on image to enlarge.

Gulf Coast tick infestation in ear of cow. Click on image to enlarge.

Gulf Coast tick. Click on image to enlarge.

Related information:

Tick Research Laboratory

Canine hepatozoonosis

‘Honey, I’m Ready’: Signals of Gulf Coast Tick

Writer: Edith A. Chenault, Ag Communications
Contact: Dr. Pete Teel, (979) 845-3253, pteel@tamu.edu

COLLEGE STATION - Communication is the key when it comes to host
attraction and the love life of the Gulf Coast tick. At least that's what Dr. Pete Teel, professor of entomology with the Texas Agricultural Experiment Station, and several of his graduate students at Texas A&M University think.

"We have observed that in Coastal and South Texas areas male ticks become active in early summer and attach to cattle four to six weeks in advance of female host-seeking activity. And we believe that this delay helps ensure the success of female bloodfeeding," Teel said.

"We have just completed an analysis of tick-count data from cattle collected during summer to fall periods over several years that suggests female ticks can discriminate and attach to cows in the herd that already have males from those that do not have males. "What's involved is a series of chemical cues starting with carbon dioxide from the cows' breath and including a cologne, or a male pheromone," that enables ticks to communicate with each other, he said.

The Gulf Coast tick - also known to ranchers as the Gulf Coast ear tick - is a pest of livestock, particularly cattle, but also affects wildlife
and pastured horses, Teel said. It also is a fairly common parasite of
dogs and has recently been found to be a vector of a protozoan called Hepatozoon americanum. It causes a disease called canine hepatozoonosis.

The adult ticks - which feed primarily on the ears of large mammals -
cause weight and blood loss, plus irritate their hosts. Their larvae and nymphs feed on small rodents and ground dwelling birds. Teel's hypothesis is that female tick selection of a host with bloodfeeding males expedites female attachment, bloodfeeding, and mating over the course of 10-12 days on the host. Then, the engorged female leaves the host to lay eggs.

The female Gulf Coast tick weighs only about 4 to 5 mg when she first gets on the host, but by the time she is bloodfed and falls back into the pasture, she may weigh a gram," Teel said. "She's increased her weight by
200 to 250 times. She is very susceptible to being mashed or groomed off. From the tick's perspective, that's a dangerous zone. Speed is of the essence."

He also suspects the female - after finding a host and bloodfed male - emits a pheromone that suppresses the male's signal for females to come to him. In the absence of females, the male keeps pumping out signals."Ticks have a variety of strategies and cues used to find hosts and obtain a bloodmeal," Teel said. "This one seems to need to detect the presence of carbon dioxide produced by the host and then the male pheromone before she will get on that host."

To conduct the research at Texas A&M, Teel and graduate students Sarah Sleeba, Hee Kim and Aaron Wexler in collaboration with Dr. Howard Williams, senior scientist with the Texas A&M departments of chemistry and entomology, used solid phase microextraction technology. This technology was developed to detect air pollutants and perform chemical analyses using gas chromatography.

The team adapted the technologies to collect the organic chemicals emitted by both males and females to determine how they communicated with one another.

The female climbs onto a host with bloodfed males and begins feeding. After four days of feeding, the male develops a spermatophore, a packet of sperm. He mates with the female, who falls back into the pasture to lay her eggs, all 15,000-18,000 of them.

The emitted chemicals from the males will be tested against other known tick pheromones to see if there is a match. If not, more research will be done to identify and characterize the chemical(s) and how they may be used against the tick.

In addition to the danger it poses now, the Gulf Coast tick was confirmed as a vector of a deadly disease called heartwater in 2000. Originally from Africa, the disease gets its name because the pericardium - or the sac around the heart - fills with fluid in cattle, sheep, goats and deer. Currently, the only way it can be accurately diagnosed is a post-mortem brain smear, and there are no practical methods of prevention or treatment.

According to climate models, heartwater could easily exist along the Gulf Coast and further inland if the disease agent comes to the United States, Teel said.

The Gulf Coast tick was the only one of three U.S. livestock ticks tested that could consistently transmit the heartwater disease agent. An African tick closely related to the Gulf Coast tick, as well as heartwater disease, arrived in the Caribbean about 160 years ago, Teel said. The tick stayed on three islands for about 140 years, and then in the late 1970s and 1980s it began to spread. Now it has been identified on a total of 17 islands. The culprit? Cattle egrets, which host the immature forms of the African tick.

The likelihood of the involvement of two ticks - the native tick and the exotic tick - could rapidly spread heartwater in North America, Teel said.

Originally, the Gulf Coast tick survived within 100 miles of the coastline of the Atlantic Ocean to the Gulf of Mexico. However, adult ticks have been collected further inland in isolated incidences - possibly transported by birds or livestock movement.

The Gulf Coast tick has also set up permanent residence in two inland states For that reason, scientists at Oklahoma State University and Kansas State University have joined in the research. Their tick is morphologically similar in shape, form and structure, but appears to have some genetic differences from the type found along the Texas Gulf Coast, Teel said.

In Texas and eastward along the Gulf Coast, the adults are active August through October. The larvae and the nymphs are active in the winter. In Oklahoma and Kansas, the adults are active in the winter and immature ticks are active in late spring and summer, about five months earlier than those in Texas. Tick control strategies between these areas have had to adjust to meet these differences.

Teel said he hopes the information gained from this research can be used against the ticks. He said pheromones might be used to attract ticks to animals. The pesticide would kill them before they had time to feed on the host. In addition, they might also be used in surveillance tactics to keep track of the tick.

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