Commonly Used Acaricides Found Effective on Invasive Tick
By Andrew Porterfield
The Asian longhorned tick (Haemaphysalis longicornis), a long-time cattle parasite in Asia, New Zealand and Australia, was discovered in the U.S. on a sheep in New Jersey in 2017, though the tick may have been in the country years earlier. Like too many invasive exotic species, it spread quickly and is now found in several eastern U.S. states. Also like invasive, exotic species, there is always a risk that it could evade eradication methods used on other ticks.
To determine if H. longicornis is resistant or susceptible to acaricide products proven to kill other ticks, Rebecca Butler, a Ph.D. student in the Department of Entomology and Plant Pathology at the University of Tennessee, and colleagues tested three spray and five pour-on acaricides to see if they were effective against the (relatively) new arrival. The results of their study, which found that all the products effectively killed H. longicornis within 24 hours of exposure, was published in July in the Journal of Medical Entomology.
The findings are important because the Asian longhorned tick poses a serious health and economic threat to the U.S. cattle industry. It feeds on a variety of wildlife, companion animal, livestock, and human hosts. It can easily transmit the pathogen Theileria orientalis, which infects cattle, and has a parthenogenic reproductive strategy—by which the ticks reproduce asexually—that increases its potential for invasiveness and ability to cause significant blood loss. This study is believed to be one of the first to demonstrate the efficacy of acaricides on the invasive tick.
Butler and her colleagues used the eight products according to label instructions, and tests were conducted in a lab environment. Nymph-stage ticks were collected from an eastern Tennessee cattle farm and, after exposure, examined for mortality at onset, one to four hours, then at 21 hours, 24 hours, and finally 48 hours.
None of a group of ticks in a control group were killed, while all treated ticks were dead within 24 hours. “It was surprising that products used in this study caused mortality so quickly after the ticks were exposed,” says Butler.
The acaricide products will be an important tool for preventing establishment of new populations of the tick and reducing their populations, since they will not be able to disperse or feed on treated hosts. While this study was conducted using Petri dishes, on-animal testing is the next logical step to determine results after spraying or applying the insecticides on cattle.
One potential concern with using these acaricides (and which is common for nearly every pesticide) is the development of resistance to the chemicals. “Overuse of acaricides could lead to resistant strains of H. longicornis and misuse of pesticides could lead to acaricide failure,” says Butler. Such resistance might be easier for the tick to develop, thanks to its parthenogenic reproductive strategy. “No H. longicornis males have been recovered from the field in the U.S. Thus, each offspring is identical, or nearly so, to its mother. It a mutation occurred in a family that rendered it resistant to an active ingredient and still allows it to produce viable offspring, a population could very quickly go from susceptible to resistant,” says Karen Vail, entomology professor at the University of Tennessee and co-author of the study.
One way around encouraging resistance (besides careful use of the insecticides) is to adopt integrated pest management techniques. Other studies showed that 96 percent of lone star ticks (Amblyomma americanum) can be controlled with proper management of habitats, proper use of acaricides, and host animal management. “Habitats can be modified to create an unfavorable environment for [H. longicornis], such as frequent mowing or bush hogging pastures, but this still needs to be evaluated,” says Butler. For now, more needs to be learned about how this tick species thrives, and what roles it plays in different environments and diseases.
Journal of Medical Entomology
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.