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Updated: Dec 14, 2025
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Published on: November 21, 2018
Physiological evidence that three known mutations in the para-sodium channel gene confer cypermethrin knockdown
Raquel Cossío-Bayúgar1, Estefan Miranda-Miranda1, Francisco Martínez-Ibañez2
1Centro Nacional de Investigaciones Disciplinarias en Salud Animal e Inocuidad, Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias (INIFAP), Cuernavaca, Morelos, Mexico.
Background:
Acaricide resistance is a central problem for the control of the cattle tick Rhipicephalus microplus. The physiological effects and phenotypes of the mutations that cause acaricide resistance are not always well understood or characterized. Single nucleotide polymorphisms (SNPs) that confer cypermethrin knockdown resistance (kdr) have been reported in R. microplus. These SNPs have been associated and correlated with pyrethroid resistance although there is no direct physiological evidence that their presence does confer kdr in this organism.
Methods:
Resistant and susceptible strain resistance profiles were obtained using the larval packet discriminating dose assay. The relevant genomic regions of the para-sodium channel were amplified using standard PCR; SNPs were detected by sequencing the corresponding amplicons. Ovary response to cypermethrin exposure/treatment was evaluated using videometrical analysis.
Results:
We found that the pyrethroid resistance trait is stable in a resistant reference strain after years without selection, suggesting that the resistance conferring mutations are fixed in the population. In this strain, a change in the structure of the pre-synaptic para-sodium channel caused by the G184C, the C190A and the T2134A SNPs appears to confer resistance. These mutations are absent in the susceptible strain used as control. We demonstrate that cypermethrin blocks ovary contraction in cypermethrin-susceptible ticks. We also show that ovaries from organisms that carry the kdr associated SNPs still contract at cypermethrin concentrations that completely block ovary contraction in the susceptible strain. The configuration of the experimental system excludes a xenobiotic detoxification mechanism.
Conclusions:
This is the first report that presents physiological evidence that the presence of the G184C, the C190A, and the T2134A mutations in the para-sodium channel correlates with maintaining muscle contractility in R. microplus exposed to cypermethrin. These SNPs may confer cypermethrin resistance in this organism by avoiding presynaptic blockage, inhibiting the flaccid muscle paralysis characteristic of this acaricide. The videometric assay that we previously validated can be used to detect more rapidly than other assays that involve larval mortality kdr-like cypermethrin resistant tick strains, permitting to directly assay adult pre-engorged females after they are collected on the field without waiting until eggs are laid and larvae eclose.
Insights
Acaricide resistance in Rhipicephalus microplus is linked to specific mutations in the para-sodium channel. These genetic changes allow ticks to maintain muscle function and survive exposure to cypermethrin.
Area of Science:
- Veterinary Entomology
- Molecular Entomology
- Toxicology
Background:
- Acaricide resistance in Rhipicephalus microplus poses a significant challenge for cattle tick control.
- The precise physiological mechanisms underlying acaricide resistance, particularly conferred by single nucleotide polymorphisms (SNPs), require further elucidation.
- While SNPs associated with cypermethrin knockdown resistance (kdr) have been identified in R. microplus, direct physiological evidence linking them to resistance is limited.
Purpose of the Study:
- To investigate the physiological effects of specific SNPs in the para-sodium channel on cypermethrin resistance in Rhipicephalus microplus.
- To provide direct physiological evidence for the role of identified SNPs in conferring resistance to cypermethrin.
- To validate a videometric assay for rapid detection of cypermethrin-resistant tick strains.
Main Methods:
- Resistance profiles of susceptible and resistant Rhipicephalus microplus strains were determined using the larval packet discriminating dose assay.
- The para-sodium channel gene was amplified via PCR, and single nucleotide polymorphisms (SNPs) were identified through sequencing.
- Ovary contractility in response to cypermethrin exposure was assessed using videometrical analysis.
Main Results:
- The pyrethroid resistance trait was found to be stable in a resistant Rhipicephalus microplus strain, indicating fixed resistance-conferring mutations.
- Specific SNPs (G184C, C190A, T2134A) in the para-sodium channel were identified in the resistant strain but absent in the susceptible strain.
- Cypermethrin blocked ovary contraction in susceptible ticks, while ovaries from ticks with kdr-associated SNPs maintained contractility at high cypermethrin concentrations, excluding detoxification mechanisms.
Conclusions:
- This study provides the first physiological evidence that G184C, C190A, and T2134A mutations in the para-sodium channel correlate with maintained muscle contractility in cypermethrin-exposed Rhipicephalus microplus.
- These SNPs likely confer cypermethrin resistance by preventing presynaptic blockage and subsequent flaccid muscle paralysis.
- The validated videometric assay offers a rapid method for detecting kdr-like cypermethrin resistance in field-collected adult ticks.
