RESUMO
A field survey was conducted in 2001 to evaluate resistance to pyrethroid and organophosphate (OP) insecticides on horn flies, Hematobia irritans irritans (L.), from seven ranches in the state of Tamaulipas, Mexico, and from three locations in central Texas. Filter papers impregnated with either technical permethrin or diazinon were used to measure the levels of resistance to pyrethroids and OPs. A multiplex polymerase chain reaction (PCR) assay was used on individual horn flies from these field populations to detect the presence of the kdr and super-kdr alleles associated with pyrethroid resistance, and a mutated alphaE7 esterase allele associated with OP resistance. Relative to a susceptible laboratory (Kerrville) strain, horn flies from Mexico exhibited 5.1- to 28.3-fold resistance to permethrin at the LC50, and 23.8- to 136-fold resistance at the LC90. Horn flies from Texas ranches exhibited only two- to five-fold resistance. All field populations of the horn fly were highly susceptible to diazinon, and no mutant alphaE7 esterase alleles were detected. The super-kdr allele was found only in a single fly from a ranch in Mexico. Results of PCR assays showed that the kdr allele was present at various frequencies in field populations of horn flies. A gender-related bias in distribution of kdr genotypes was found in horn flies from Mexico, but not in horn flies from Texas. The overall kdr allelic frequencies in horn flies from Mexico were 23.2-37.8% higher in females than in males. Regression analysis revealed a significant correlation between kdr allelic frequencies and the levels of knockdown resistance to permethrin among the horn fly populations studied. The results validate the role of the PCR-based molecular assay as a diagnostic tool in monitoring resistance to pyrethroids and also provide useful information on population genetics of horn fly resistance to pyrethroids and OPs.
Assuntos
Diazinon/toxicidade , Resistência a Inseticidas/genética , Muscidae/genética , Permetrina/toxicidade , Alelos , Animais , Sequência de Bases , Bioensaio , Primers do DNA , Frequência do Gene , Geografia , México , Reação em Cadeia da Polimerase/métodos , Análise de Regressão , TexasRESUMO
El objetivo del presente estudio fue determinar la dinámica poblacional de H. irritans en un hato de bovinos de Soto la Marina, Tamaulipas, México; con ese propósito se obtuvieron conteos de esa mosca mediante la observación directa (OD) sobre 12 bovinos en pastoreo y sin tratamiento mosquicida. A partir del 6 de septiembre de 1998 al 29 de agosto de 1999, en el Rancho "Los Pinos", municipio de Soto la Marina, Tamaulipas, se determinó la correlación entre la población de moscas con los factores climáticos de temperatura (T) y precipitación pluvial (PP). La presencia de H. irritans durante el año fue continua, con picos poblacionales mayores de 200 moscas por animal en septiembre, abril, mayo y junio, y poblaciones menores de 100 moscas por animal en noviembre, diciembre, enero, julio y agosto. La correlación entre la población de moscas con la T fue de 0.57 (P < 0.05), y con la PP, de 0.32 (P < 0.05). El análisis de las dos variables, en conjunto, mostró una correlación de 0.70 (P < 0.05). Se concluye que H. irritans se encuentra presente durante todo el año en el rancho en estudio, con variaciones relacionadas con las variables climatológicas de T y PP.