New research angles could end nilgai killings

RIO HONDO — Scientists working at the Russell Ranch here seem unconcerned about setting loose billions of known killers in the Rio Grande Valley.

But if it works, an experimental process against cattle fever ticks could mean the end of the controversial aerial culling of hundreds of nilgai antelope at nearby Laguna Atascosa National Wildlife Refuge.

Researchers are devising a system to attack cattle fever ticks with a microscopic worm called a nematode. Using a water jet frothing with live versions of the worm, U.S. Department of Agriculture officials are spritzing nilgai in the field, hoping they can kill the notoriously resilient ticks.

“The nilgai antelope is the key alternative host for the cattle fever tick,” said John Goolsby, a USDA research scientist leading the effort here at the Russell Ranch. “It’s no surprise that the cattle fever tick gets on nilgai, because they both come from India, the tick and the nilgai.”

The event yesterday was part of a fact-finding mission by U.S. Rep. Filemon Vela (D-Brownsville). Vela said he is concerned about both the spread of the cattle fever tick and finding alternatives to the U.S. Fish and Wildlife Service’s helicopter culls of non-native nilgai at nearby Laguna Atascosa Wildlife Refuge.

“What’s our estimated population of nilgai, and what’s the geographic border?” Vela asked.

“There are about 30,000 in South Texas now, and it’s very difficult to get an accurate census of them because they’re so elusive,” Goolsby said. “They occur in Cameron, Willacy and Kleberg counties, but they’re expanding their range. They’re beginning to go further west and further north.”

“They can pick up the tick and move it far and wide,” he added.

Long march against ticks

The fever ticks can carry a disease fatal to cattle called babesiosis, which has at times in U.S. history been a scourge of cattle and ranchers and remains a threat today to Texas’ $12 billion-a-year beef industry.

A massive effort to eliminate the cattle fever tick early last century was a success by 1943 but the ticks which are endemic to Mexico periodically push northward into South Texas.

A permanent quarantine zone was established along the Rio Grande and extends 500 miles from Brownsville up the Valley in hopes of detecting and containing any cattle fever tick spillover from Mexico.

Quarantine zone notwithstanding, we’re in one of those cattle fever tick irruptions right now, with fever ticks discovered as far north as Live Oak County. That has cattle ranchers as well as federal and state officials worried, even though no “hot ticks” actually carrying babesiosis have been found.

Enter the nilgai sprayer

Cattle fever ticks are highly specialized parasites and only attach themselves to cows, nilgai or white-tailed deer.

Ranchers can dip cattle as often as every two weeks at a high cost in manpower and the health of the cows, and deer can be treated with ivermectin-laced corn and anti-tick insecticides they rub against at salt blocks and feeding stations.

None of it works on nilgai.

“Creating some way to treat the nilgai is so important, Congressman, because we can bring them into this common latrine, which is a unique part of their biology, they come in on to the latrine,” Goolsby said.

“On their own?” Vela asked.

“On their own, nightly, males and females,” Goolsby said. “People wonder, ‘why do they make these common latrines?’ Well, when you think about nilgai, they come from India, right?

“What’s the other really popular animal in India? It’s the Bengal tiger,” he added. “Nilgai have evolved to make latrines so they can hide their smell, their scent from their key predator, the Bengali tiger … the tiger can’t really figure out where they’re eating.”

This is the trait researchers are exploiting to treat them with nematodes to kill ticks.

“What we’ve developed here is a parasitic nematode worm that is commercially available,” Goolsby said. “We can put this nematode into the sprayer and it’s already right here in the environment anyway so we’re not introducing anything harsh.”

As he handled a package of live nematodes, he said the one-pound package of what resembles cake mix actually holds 1.5 billion live worms, which can survive in that package for three months.

This particular nematode is no stranger to the Valley. The strain used commercially originated in Cameron County, and initially was tasked to fight the cotton pest known as the boll weevil. Today it is commonly used on Valley and Florida citrus to fight a root weevil.

“It’s good at penetrating and finding its host, and it can be reared economically, so we have something that’s really benign on the environment,” Goolsby said. “We have tested it at the tick lab at Moore Air Base and it does kill the ticks.”

To demonstrate the spraying apparatus USDA is using, Goolsby spooned some live nematodes into the water in a plastic bowl of an experimental machine that mixes the worms with water. It is linked to a cooler with a 12-volt battery inside and a sensor that when tripped spritzes some nematodes and water through hoses onto a nilgai’s legs and belly, where ticks congregate.

The nematode delivery prototype cost about $1,000 he said, although he believes the price can be reduced to around $300 per unit as more are ordered.

The nilgai pretty much ignore it as both do their business.

Other research ongoing

Current USDA research goes beyond nematodes, Goolsby said, producing a small cardboard box which he said is used to drop parasitic wasps from planes so they can prey on cattle fever ticks, too.

He said research into these wasps, which are native to Vietnam, is ongoing and could be another weapon in the USDA’s holster when it comes to battling cattle fever ticks.

Another weapon against the cattle fever tick, and perhaps this is the most important one, is knowledge.

Ricardo Adobbati, a Brownsville attorney, is a board member with the nonprofit Las Huellas (The Tracks), which is an advocacy group for South Texas wildlife, wildlife managers, landowners and sportsmen.

His group is funding research by one graduate student from Texas A&M-Kingsville into DNA testing of droppings found at communal nilgai latrines. Knowing just which nilgai are using which latrines will be crucial in determining how many nematode sprayers are needed to be effective against the ticks.

“Because the patterns are what are most important,” Adobatti said. “These latrines, you only need as many as the areas you wish to cover. So if you have a nilgai traveling 20-30 miles then the number of the latrines in the study can be less.

“We’ve already got one grad student doing the work, and we’re hopeful we can get one more through more funds that we raise through the organization,” he added.

For his part, Goolsby is happy to have help.

“We just cannot look at this the way we did 50-60 years ago, I mean things are changing, and we need to adapt as researchers,” he said. “We’ve got a lot of good ideas — not just me — but a group of researchers if we can come together we can develop tools for the future to make it sustainable.”

“Internally, they’ve raised their own money here in Cameron County, and said ‘We want to be part of the solution to cattle fever ticks,’” Goolsby added. “Without private money from the organization, I certainly wouldn’t have made this much progress.”

Facts on nilgai research

Female nilgai have huge ranges of up to 74,000 square acres (115 square miles)

Male nilgai have ranges of about 5,000 square acres

White-tailed deer have an average range of 1,200 square acres

Nilgai use communal latrines, a habit which is being co-opted to treat them for cattle fever ticks

Such communal latrines are believed to be an instinctive defense by nilgai against India’s tigers

Killing cattle fever ticks

  • Research at Russell Ranch uses an automatic spraying system to spritz nilgai with water containing nematodes
  • Nematodes attack and kill cattle fever ticks
  • Nematodes have been farmed for use against boll weevils, citrus root weevils
  • Original nematode stock now in commercial use came from Cameron County
  • Research progressing into using parasitic wasps from Asia to attack ticks

Cattle fever tick hosts

  • Cattle, white-tailed deer and nilgai
  • This species of tick doesn’t latch onto horses, javelina or feral hogs, coyotes, birds, rabbits or hares