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El objetivo del estudio fue determinar la susceptibilidad de Haematobia irritans (L.) a los insecticidas por medio de una prueba in vitro permetrina (2.5 y 6.0 &x00B5; g/cm2) y diazinon (0.01 y 0.06 &x00B5; g/cm2). Tambien se realizo un estudio detallado por encuesta del tipo de manejo de los pesticidas al norte de Veracruz (Mexico) durante 1998 y 2000 y la parte central de Nuevo Leon (Mexico) en 2000. Para valorar el porcentaje de mortalidad de la mosca del cuerno se utilizaron bioensayos con dos dosis discriminantes de permetrina o diazinon, impregnados en frascos. Los resultados mostraron que el porcentaje de mortalidad para permetrina en Nuevo Le& x00F3;n y Veracruz fue poco significativo e inexistente, respectivamente. La aplicaci& x00F3;n de una encuesta a trav& x00E9;s de cuestionarios sobre el uso de & x00E9;stos y otros pesticidas tambi& x00E9;n revel& x00F3; que los organofosforados fueron los m& x00E1;s utilizados para el control de esta plaga en Nuevo Le& x00F3;n, mientras que los piretroides fueron los m& x00E1;s utilizados en Veracruz.

The objective of this study was to assess the percentage of resistance of Haematobia irritans (L.) by means of an in vitro test of mortality percentage to permethrin (2.5 and 6.0 µg/cm² ) and diazinon (0.01 and 0.06 µg/cm² ). Flies were collected from 14 beef-cattle production units. A detailed survey on pesticide management at northern Veracruz (Mexico) during 1998 and 2000 and the central part of Nuevo Leon in 2000 (Mexico) were carried out as well. Bioassays to assess mortality of horn flies were carried out based on jars soaked in two discriminating doses of permethrin or diazinon. Horn flies were directly collected from cattle under field conditions and immediately exposed to permethrin and diazinon. Fly mortality was recorded for no longer than 2 h. Results showed that the mortality percentage for permethrin in Nuevo Leon and Veracruz was either very low or non-existent, respectively. In contrast, the mortality percentage exhibited by diazinon was much higher (P < 0.05) in both experimental areas. However, this percentage decreased in Veracruz from one year to the next. Also, a survey through questionnaires on the use of these and other pesticides revealed that organophosphates were widely used for pest control in Nuevo Leon, whereas pyrethroids were more often used in Veracruz. The survey revealed that product inefficiency was the main reason for changing chemical group. Treatments on cattle were mostly applied by spraying the pesticides in both Mexican States. In most of the cases (86.7%), producers and/or veterinarians sprayed animals for more than 10 treatments along the year. This study allows the conclusion that there is a generalized resistance to permethrin in these two States and that horn fly populations did not show resistance to diazinon in either working areas. [ABSTRACT FROM AUTHOR]