Molecular survey of pyrethroid resistance mechanisms in Mexican field populations of Rhipicephalus (Boophilus) microplus

Authors: ROSARIO CRUZ, RODRIGO - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); Guerrero, Felicito; Miller, Robert; RODRIGUEZ-VIVAS, R - Autonomous University Of Yucatan; TIJERINA, MARY - Agricultural Marketing Service (AMS, USDA); DOMINGUEZ-GARCIA, D - Metropolitan Autonomous University; HERNANDEZ-ORTIZ, R - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); CORNEL, A - University Of California; MCABEE, R - University Of California; ALONSO-DIAZ, M - Universidad Nacional Autonoma De Mexico

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2009
Publication Date: 6/30/2009
Citation: Rosario Cruz, R., Guerrero, F., Miller, R., Rodriguez-Vivas, R.I., Tijerina, M., Dominguez-Garcia, D.I., Hernandez-Ortiz, R., Cornel, A.J., Mcabee, R.D., Alonso-Diaz, M.A. 2009. Molecular survey of pyrethroid resistance mechanisms in Mexican field populations of Rhipicephalus (Boophilus) microplus. Parasitology Research. 105:1145-1153.

Interpretive Summary: Many populations of cattle ticks, Rhipicephalus microplus, from Mexico have developed varying degrees of resistance to the pyrethroid class of pesticides. Knowledge of the severity of this resistance problem can guide tick control programs in Mexico. Susceptibility to pyrethroids and the mechanisms of resistance were evaluated in 28 Rhipicephalus microplus tick populations from Mexico. Resistance levels were determined by several well established methods, including the larval packet test bioassay, the DNA-based knockdown resistance PCR assay, and tests for metabolic esterase activity assays. The sampled tick populations were tested for resistance to the pyrethroids cypermethrin, flumethrin and deltamethrin. Metabolic esterase activity did not have a significant role in the pyrethroid resistance in these populations. However the presence of the sodium channel mutation as measured by the PCR assay was highly correlated with resistance and the level of resistance as measured by bioassays. Over half the populations (16/28) were cross-resistant to flumethrin, deltamethrin and cypermethrin, 21.4% of the samples (6/28) were susceptible to all three pyrethroids, 10.7% of the samples (3/28) were resistant to flumethrin only, 3.4% of the samples (1/28) were resistant to deltamethrin only and 7.1% (2/28) were resistant to flumethrin and deltamethrin. Target site-based resistance, as conferred by the sodium channel mutation was the major mechanism of pyrethroid resistance in these populations.

Technical Abstract: Susceptibility to synthetic pyrethroids (SP´s) and the role of two major resistance mechanisms were evaluated in Mexican Rhipicephalus microplus tick populations. Larval packet test (LPT), knock-down (kdr) PCR allele-specific assay (PASA) and esterase activity assays were conducted in tick populations for cypermethrin, flumethrin and deltamethrin. Esterase activity did not have a significant correlation with SP´s resistance. However a significant correlation (p<0.01) was found between the presence of the sodium channel mutation, and resistance to SP´s as measured by PASA and LPT respectively. Just over half the populations (16/28) were cross-resistant to flumethrin, deltamethrin and cypermethrine, 21.4% of the samples (6/28) were susceptible to all of the three pyrethroids 10.7 of the samples (3/28) were resistant to flumethrin, 3.4 of the samples (1/28) were resistant to deltamethrin only and 7.1% (2/28) were resistant to flumethrin and deltamethrin. The presence of the kdr mutation correlates with resistance to the SP´s as a class. Target site insensitivity is the major mechanism of resistance to SP´s in Mexican R. microplus field strains, involving the presence of a sodium channel mutation, however, esterase-based, other mutations or combination of mechanisms can also occur.