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Title: ROLE OF KDR AND ESTERASE-MEDIATED METABOLISM IN PYRETHROID RESISTANT POPULATIONS OF HAEMATOBIA IRRITANS IRRITANS (DIPTERA: MUSCIDAE) IN BRAZIL

Author
item Guerrero, Felicito
item BARROS, THADEU

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2006
Publication Date: 9/1/2006
Citation: Guerrero, F., Barros, T. 2006. Role of kdr and esterase-mediated metabolism in pyrethroid resistant populations of Haematobia irritans irritans (Diptera: Muscidae) in Brazil. Journal of Medical Entomology. 43(5):896-901.

Interpretive Summary: The horn fly, Haematobia irritans irritans (L.) has become a problem for Brazilian cattle producers even though its introduction into Brazil is a relatively recent event. Ranchers control the fly with insecticides, however, control failure is becoming an increasing concern. Several ranches from the state of Mato Grosso do Sul were surveyed for the existence of pyrethroid resistance. Bioassay results showed that pyrethroid resistance was widespread and reached high levels in horn fly populations throughout the state. One population, Estrela do Oeste, was highly resistant (704-fold more resistant than the susceptible control population) and appeared to have highly active insecticide-metabolizing enzymes in addition to a mutation in the target site of the insecticide activity which has been shown to cause resistance in horn flies in Mexico and the U. S. Both the target site insensitivity (kdr) and esterase-mediated metabolism mechanisms occur in other horn fly populations in Mato Grosso do Sul state. However, it appears that there is a third mechanism causing pyrethroid resistance in most of these populations and characterization of this mechanism is ongoing.

Technical Abstract: The horn fly, Haematobia irritans irritans (L.) has become a problem for Brazilian cattle producers even though its introduction into Brazil is a relatively recent event. Control failure is becoming a concern and several ranches from the state of Mato Grosso do Sul were surveyed for the existence of pyrethroid resistance. Bioassay results showed that cypermethrin resistance was widespread and reached high levels in horn fly populations throughout the state, with resistance factors (RF) ranging from 50.4 to 704.8. Synergist bioassays failed to detect a major role for esterases as a mechanism of pyrethroid resistance mechanisms in these populations except for the highly pyrethroid resistant Estrela do Oeste population (RF=704.8). The superkdr mutation was not found in any flies. The kdr mutation was not detected in 8 of the 13 populations and 4 populations had < 7% of individuals which possessed the kdr mutation. However, 50% of the tested flies had the kdr mutation in the Estrela do Oeste population. Both the target site insensitivity (kdr) and esterase-mediated metabolism mechanisms occur in horn fly populations in Mato Grosso do Sul state, but it appears that they are not the major mechanism causing pyrethroid resistance in most of these populations.