First Report of Permethrin-Resistant Boophilus microplus (Acari: Ixodidae) Collected Within the United States

• Published in: Journal of medical entomology 2007-03, Vol.44 (2), p.308-315
• Main Authors: Miller, Robert J., Davey, Ronald B., George, John E.
• Format: Article
• Language: English
• Subjects: acaricide; acaricide resistance; amino acid substitution; Animals; Arachnida; Biological and medical sciences; Biological Assay; Boophilus microplus; Cattle; Cattle Diseases - parasitology; Cattle Diseases - prevention & control; Female; Fundamental and applied biological sciences. Psychology; Insecticide Resistance - genetics; Insecticides - toxicity; Invertebrates; Ixodidae - drug effects; Ixodidae - genetics; Larva; Medically important nuisances and vectors, pests of stored products and materials: population survey and control; mutation; Naphthols - metabolism; permethrin; Permethrin - toxicity; permethrin resistance; pesticide resistance; pesticide synergists; Polymerase Chain Reaction; resistance mechanisms; resistance selection; Rhipicephalus (Boophilus) microplus; selection response; sodium channel gene; sodium channels; Sodium Channels - genetics; Tick Infestations - prevention & control; Tick Infestations - veterinary; United States; VECTOR/PATHOGEN/HOST INTERACTION, TRANSMISSION; Vectors. Intermediate hosts
• ISSN: 0022-2585; 1938-2928
• DOI: 10.1603/0022-2585%282007%2944%5B308%3AFROPBM%5D2.0.CO%3B2

Boophilus microplus (Canestrini) (Acari: Ixodidae), collected in Hidalgo County, TX, were determined to be resistant to permethrin. Discriminating dose (DD) tests at the LC99 and 2× the LC99 of susceptible ticks yielded lower than expected mortalities for permethrin but not for coumaphos or amitraz acaricides. Initial bioassay results confirmed the pyrethroid resistance detected in the DD assays. Two generations of selection with permethrin at a rate >60% increased the measured resistance ratios from 9.5 (7.9–11.5) to 263 (217–320). Synergist studies suggested that metabolic enzymes were involved in permethrin resistance. Native gel electrophoresis verified that the CZS9 esterase was not involved in resistance to permethrin. Polymerase chain reaction examination revealed the presence of a mutation of the sodium channel gene (Phe[arrow]Ile amino acid substitution in the S6 trans-membrane segment of domain III), in the resistant B&H population. The frequency of this mutation increased after selection with permethrin and concurrent increase in estimated resistance ratios. The B&H population was eradicated from the United States by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service Veterinary Services, Cattle Fever Tick Eradication Program through the use of the organophosphate acaricide coumaphos.