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Title: Inheritance of pyrethroid resistance and a sodium channel gene mutation in the cattle tick Boophilus microplus

item Miller, Robert

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2008
Publication Date: 6/5/2008
Citation: Aguilar-Tipacamu, G., Miller, R., Hernandez-Ortiz, R., Vasquez-Pelaez, C., Garcia-Vazquez, Z., Rodriguez-Vivas, R., Fragosa-Sanchez, H., Olvera-Valencia, F., Rosario-Cruz, R. 2008. Inheritance of pyrethroid resistance and a sodium channel gene mutation in the cattle tick Boophilus microplus. Parasitology Research. 103:633-639.

Interpretive Summary: Pesticide resistance in the southern cattle tick, Boophilus microplus, is a threat to the success of the Cattle Fever Tick Eradication Program (CFTEP). Pyrethroid resistance is important because its presence eliminates the potential use of this important class of pesticide in the CFTEP. In this study, we show that the inheritance pattern of pyrethroid resistance is as an incompletely recessive trait that it is modified by the sex of the parents. Resistant females mated with susceptible males produce offspring that are more resistant than when susceptible females are mated with resistant males. Knowing the mode of inheritance of resistance to this important pesticide will allow ranchers to better control the development of resistant ticks on their animals. It will also lead to further research on the genetic control of this type resistance and allow for the continued use of this chemical in the future. Additionally, if it became necessary to use pyrethroids to eradicate ticks in the CFTEP, knowing the inheritance pattern of this chemical will provide VS, APHIS Inspectors and ARS Scientists with the information needed to make rational eradication decisions.

Technical Abstract: A single nucleotide polymorphism (SNP) producing a substitution (Phe'Ile), within the S6 transmembrane segment at domain III within the sodium channel gene sequence, has been associated with pyrethroid resistance in the cattle tick Boophilus microplus. The aim of the present study was to analyze the inheritance of the mutant allele, derived from reciprocal crosses of a susceptible and a resistant strain. Two B. microplus tick strains were used, B&H (resistant to pyrethroids) and Media Joya (MJ, susceptible reference strain). Reciprocal crosses between the parental strains, B&H and MJ (B&H' X MJ' and MJ' X B&H') were made. Bioassays were carried out to test resistance to cypermethrin, deltamethrin and flumethrin. Genotypes were determined by an Allele Specific Polymerase Chain Reaction. The resistance allele frequency of both parental strains, were 100% and 2.27% for resistant B&H and susceptible MJ, respectively. The reciprocal crosses show a predominance of the heterozygote genotype, which explains the significant decrease of the acaricide resistance to all three pyrethroids. However, the B&H' X MJ' progeny showed a complete recessive survival (DML=0) for deltamethrin and flumethrin, which can be interpreted as a complete dominance of the wild type (susceptible) allele, and incomplete dominance for cypermethrin (DML=0.169). On the other hand, MJ' X B&H' progeny showed a partially recessive survival for cypermethrin (DML=0.380), deltamethrin (DML=0.319) and flumethrin (DML=0.258), indicative of a partially dominant inheritance of the resistance.