Roles Played by Esterase Activity and by a Sodium Channel Mutation Involved in Pyrethroid Resistance in Populations of <I>Boophilus microplus</I> (Acari: Ixodidae) Collected from Yucatan, Mexico

Abstract

Pyrethroid resistance in Boophilus microplus (Canestrini) (Acari: Ixodidae) was studied by correlating discriminating-dose (DD) bioassay results and esterase activity or the frequency of a sodium channel mutation known to be involved in pyrethroid resistance in nine field strains of B. microplus from Yucatan, Mexico. Two tick strains (P67 and B74) were identified as susceptible to cypermethrin, deltamethrin, and flumethrin by DD, one strain (P65) was susceptible to cypermethrin and resistant to deltamethrin and flumethrin, and six strains were resistant to cypermethrin, delta-methrin, and flumethrin (T11, M10, C54, R49, B71, and T66). By using polymerase chain reaction, only 6.0 and 6.2% of resistance allele (R) was found in the susceptible strains (P67 and B74, respectively). In the T66 strain, with 100% of larval survival to the DD of pyrethroids as measured by the larval packet test (LPT), 98.0% of the gene pool contained the R allele. Positive correlations between the larval survival and the percentage of the R allele were found (deltamethrin r2 = 0.8875, P < 0.01; cypermethrin r2 = 0.8563, P < 0.01; and flumethrin r2 = 0.8491, P < 0.01). There were no significant correlations between the level of larval survival and esterase-based hydrolytic activity. It was concluded that within the B. microplus populations studied, resistance to flumethrin, deltamethrin, or cypermethrin was because of the novel sodium channel mutation (Phe-->Ile amino acid substitution in the S6 transmembrane segment of domain III), and there was a correlation between tick mortality by pyrethroid exposure (larval survival) and the presence of R allele. It was not determined whether enhanced esterase-based hydrolytic activity was involved in pyrethroid resistance in the populations tested.

Acaricide resistance mechanisms in Rhipicephalus (Boophilus) microplus

“…A PCR diagnostic assay (GUERRERO et al, 2001) was developed that allowed the rapid detection of this amino acid substitution in individual ticks, larvae or eggs. Large numbers of ticks were assayed by this method and this target site mechanism was found to be widespread throughout Mexico (ROSARIO-CRUZ et al, 2005 and in an outbreak strain in the United States (MILLER et al, 2007). The location of this sodium channel mutation is a bit out of the ordinary, as more arthropod sodium channel pyrethroid resistance-causing mutations are located in Domain II than the other three domains (SODERLUND; KNIPPLE, 2003).…”

Multiple mutations in the para -sodium channel gene are associated with pyrethroid resistance in Rhipicephalus microplus from the United States and Mexico

“…This is highlighted by an increasing number of infestations in the TEQA and beyond that have been found in recent years to be resistant [19,20]. Nearly all resistant infestations discovered within the U.S. are associated with pyrethroid acaricides, however, resistance to multiple acaricide classes (including coumaphos) has been described in the U.S. [14,19] and Mexico [21,22]. Pyrethroid resistance was first discovered in Mexico in 1994, shortly after the introduction of pyrethroids into the Mexican cattle market in the 1980s [23].…”

Acaricide resistance of Rhipicephalus (Boophilus) microplus in State of Mato Grosso do Sul, Brazil

“…This assay detects a nucleotide difference that causes Phe to Ile amino acid substitution in the S6 transmembrane segment of domain III of the para-like sodium channel, and it clearly distinguishes heterozygotes from homozygotes (GUERRERO et al, 2001). Studies have shown that this mutation correlates with flumethrin, deltamethrin and cypermethrin resistance in Mexican tick populations (JAMROZ et al, 2000;ROSARIO-CRUZ et al, 2005).…”