A novel amino acid substitution in the para-sodium channel gene in Rhipicephalus microplus (Acari: Ixodidae) associated with knockdown resistance.

Resistance acquired by the tick Rhipicephalus microplus (Canestrini) to different types of ixodicides in Mexico has had a negative impact on national and local livestock, mainly due to the transmission of diseases such as babesiosis and anaplasmosis, among others. The technique used for the diagnosis of resistance was that in the bioassays noted in the Norma Oficial Mexicana (NOM-006-ZOO-1994). The purpose of this investigation was the determination of resistance to pyrethroids through isoleucine-phenylalanine mutation in the gene KDR, in a population of ticks from Montemorelos, NL, Mexico. Preliminary bioassays demonstrated resistance to cypermethrin and deltamethrin (27.4%) and flumethrin (36.7-34.7%). To identify the mutation, DNA was extracted from 100 mg of larvae (pools), 10 pools were assessed by PCR, in which a pair of primers designed with the program Oligo 2.0 and Amplify 1.2 amplified a 136 bp fragment containing the mutation. The PCR product was subsequently sequenced to confirm the presence of the mutation. A strain susceptible to pyrethroid insecticides (Mora strain) was used as control, but it did not show the mutation. However, the mutation was detected in 4 out of 10 samples of the strain Montemorelos.