Researchers at the USDA-Agricultural Research Service examined the effectiveness of two organic dusts, known as Surround and CimeXa, when applied directly to lone star tick (Amblyomma americanum) larvae and nymphs (shown here). The lone star tick was used in the study as a model, as the researchers hope the dusts could be a useful tool against other tick species that transmit deadly pathogens to livestock. (Photo credit: James Gathany, CDC Public Health Image Library)

By Leslie Mertz, Ph.D.

Two organic dusts are extremely effective in battling lone star ticks, a major human-biting and disease-carrying tick in the United States, according to a new study published in September in the Journal of Medical Entomology by scientists at the U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS).

Leslie Mertz, Ph.D.

Not only that, but the dusts may also be effective against cattle fever ticks, which carry a protozoan that causes up to 90 percent mortality in cows not previously exposed, according to the Texas Animal Health Commission.

The researchers’ primary interest in conducting the study was actually the tick species Rhipicephalus (Boophilus) microplus and R. (B.) annulatus, both sometimes known as cattle fever ticks, but because these ticks are under quarantine, the researchers turned to lone star ticks (Amblyomma americanum) as a model, says senior author Allan Showler, Ph.D., research entomologist at the USDA-ARS Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville, Texas. A permanent quarantine zone runs along the Lower Rio Grande Valley on the Texas border to help keep cattle fever ticks contained to that area and prevent more from spreading north out of Mexico, where they are abundant. A few outbreaks of cattle fever ticks in Texas herds in 2016 have led to additional quarantines in several southern Texas counties.

The lone star tick is a good model for two reasons, Showler says. For one, he has access to a large colony of these arthropods in his research center, which is well north of the quarantined areas. The other benefit of the lone star tick is that the larvae are larger and more robust than those of cattle fever tick larvae, he says, so measures that work against lone star tick larvae are anticipated to be at least as effective against cattle fever ticks.

Get Them Young

The researchers wanted to catch the ticks before they get onto the host animals; for cattle fever ticks, that means the larval stage. Unlike most other ticks, cattle fever ticks are one-host parasites: Once a cattle tick larva crawls onto a host animal, it stays there through adulthood, Showler explains. In contrast, many other ticks utilize multiple hosts and can be found in vegetation at all of their life stages: larva, nymph, and adult.

Part of a research study at the U.S. Department of Agriculture’s Agricultural Research Service in Texas involved applying a dry silicate dust, known as CimeXa, to tick-infested cordgrass. The field tests showed a nearly 100 percent reduction in tick larvae. (Photo credit: Weste Osbrink, Ph.D.)

Research entomologist Allan Showler, at the U.S. Department of Agriculture’s Agricultural Research Service, is studying two organic dusts as a way to combat ticks that cause human and cattle diseases. One is a clay dust called kaolin, which is sold under the trade name Surround, and the other is a silicate dust sold as CimeXa. (Photo credit: Weste Osbrink, Ph.D.)

The researchers’ next consideration was the type of control measure to study. “Since much of the quarantined area is made up of wildlife refuges, we started to think about larval tick controls that are inert, non-toxic and safe environmentally,” Showler says. Two came to mind. One is a clay dust called kaolin, which is sold under the trade name Surround and works by glomming onto and abrading the protective, waxy cuticle that enshrouds the larval tick body. The other is a silicate dust sold as CimeXa, which works by destroying the cuticle. Both actions cause the larva to lose water and shrivel up.

Although each of the two dusts showed high mortality in larval lone star ticks, CimeXa showed a slight advantage in dry-dust applications. CimeXa killed almost every single tick larva within 24 hours, regardless of whether the researchers applied the dry dust directly onto the larva or coated the substrate with the dust and allowed the larva to simply crawl across it. Separate tests of the dust on lone star nymphs (instead of larvae) showed a nearly 100 percent kill rate with direct application of CimeXa by 24 hours, and more than 80 percent dead with the substrate test at the 48-hour mark.

After the lab tests, the research group followed up by trying CimeXa on ticks in a natural environment. Specifically, they sprayed the dry CimeXa dust onto grass clumps holding heavy populations of wild ticks, in this case Gulf Coast ticks (Amblyomma maculatum). Although problematic high winds made dust application less than ideal, the dry dust knocked down the number of tick larvae by 96 percent and nymphs by 100 percent. “Even though CimeXa is really light and fluffy, and we lost a lot of it in the wind, it decimated those ticks,” Showler says.

A study conducted by U.S. Department of Agriculture’s Agricultural Research Service in Texas examined the effectiveness of two organic dusts, known as Surround and CimeXa, when applied directly to lone star tick (Amblyomma americanum) larvae and nymphs. In the tests, CimeXa proved to be extremely effective, killing all the larvae and almost all the nymphs within 24 hours. (Chart originally published in Showler et al 2018, Journal of Medical Entomology)

A study conducted by U.S. Department of Agriculture’s Agricultural Research Service in Texas examined the effectiveness of two organic dusts, known as Surround and CimeXa, when applied to a substrate (the bottom of a petri dish) that lone star larvae and nymphs then walked across. Both CimeXa and Surround were highly effective against the larvae, in particular. (Chart originally published in Showler et al 2018, Journal of Medical Entomology)

Next Steps

With these results on lone star and Gulf Coast tick larvae, Showler and his colleagues are now planning additional experiments to determine CimeXa’s impact on non-target species, especially beneficial insects and other arthropods. The researchers are also in the midst of a study to test CimeXa on ticks that are already on cattle. Preliminary data are beginning to come in, and he hopes to publish those results by the end of the year.

“The whole idea of all this work is to test a variety of different tactics against cattle fever ticks, as well as other ticks, both on- and off-host. And, in particular, we’re looking for organic alternatives to conventional synthetic pesticides, which will be useful in protected areas, such as the very significant percentage of wildlife refuge land on the South Texas coastal plains and Lower Rio Grande Valley,” he says. “We need something that will be acceptable to the stewards of those lands, and we need something that works.”

Leslie Mertz, Ph.D., teaches summer field-biology courses, writes about science, and runs an educational insect-identification website, www.knowyourinsects.org. She resides in northern Michigan.