Scientists at USDA's Agricultural Research Service (ARS) are making headway in efforts to monitor pesticide resistance in Mexican cattle fever ticks.

The ticks, which transmit a serious livestock disease known as bovine babesiosis, were eradicated from the U.S. nearly 60 years ago. But they still persist in Mexican cattle, many of which cross the border for U.S. markets.

To prevent a costly re-infestation, U.S.-bound animals are dipped in coumaphos, an organophosphate pesticide that kills the ticks. But some Mexican ticks have developed resistance to coumaphos and other pesticides used in Mexico.

To help monitor this problem, ARS scientists have adapted a test that uses color to recognize coumaphos-resistant ticks and can be performed on crushed tick larvae or dissected adult tick brains. They're working to clone the tick genes involved in coumaphos resistance and will develop rapid tests for detecting them.

Researchers also have identified two independent mechanisms by which ticks become resistant to pyrethroid pesticides still used in Mexico. And they have found one strain of resistant Mexican tick possessing a gene that produces a large amount of a specific esterase protein involved in the breakdown of pyrethroids.

What's more, the researchers have shortened the time needed to spot pyrethroid resistance in a specimen from six weeks to just one day. Though pyrethroid resistance is becoming widespread, it's not found everywhere in Mexico, so pyrethroids can still play a role in killing ticks and preventing cattle disease.

Improved production traits in cattle and solutions to certain human health problems may be some of the payoff for mapping the bovine genome — a project scientists expect to complete as soon as February 2003.

Since spring 2000, scientists at ARS have been collaborating with labs around the world to develop a bacterial artificial chromosome (BAC) map, a collection of overlapping clones that represent the entire bovine genome.

Once the project is complete, scientists may be able to more accurately select genetically superior animals for specific purposes, such as lean beef, milk production or reduced feed requirements. This research may also help the medical community, since cattle and humans have many of the same genes. Scientists will be able to compare the genetic maps of each species to possibly find cures for diseases.

The two-step mapping project entails fingerprinting each of 280,000 cattle BAC clones and then sequencing both ends of each clone. Fingerprinting is done by cutting DNA from a BAC clone into pieces and separating the fragments on a gel. Researchers use the fingerprint pattern of the different fragments to identify overlapping BAC clones. Then the scientists combine the end-sequencing and fingerprinting information to determine the overlapping BAC clones.

So far, 249,000 of the 280,000 cattle BAC clones have been fingerprinted, and the end-sequencing effort is under way.

For more information, contact ARS at 301/504-1617.

“Research Roundup” is compiled by Diana Barto. Submit items to or 952/851-4671.