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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR BIOLOGY AND PHYSIOLOGY OF BITING FLIES AFFECTING LIVESTOCK

Location: Tick and Biting Fly Research

Title: Knockdown resistance in pyrethroid-resistant horn fly (Diptera: Muscidae) populations in Brazil

Authors
item Sabatini, Gustavo -
item Ribolla, Paulo -
item Barros, Antonio -
item Guerrero, Felix
item Schumaker, Terezinha -

Submitted to: Revista Brasileira de Parasitologia Veterinaria
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2009
Publication Date: July 14, 2009
Citation: Sabatini, G.A., Ribolla, P.E., Barros, A.T., Guerrero, F., Schumaker, T.T. 2009. Knockdown resistance in pyrethroid-resistant horn fly (Diptera: Muscidae) populations in Brazil. Revista Brasileira de Parasitologia Veterinaria. 18(3):8-14.

Interpretive Summary: Pyrethroid resistance is often mediated through target site resistance, which arises due to specific mutations in the sodium channel gene which influence the ability of pyrethroids to bind their target site on the sodium channel. In Brazil, the horn fly has become increasingly resistant to pyrethroids. To investigate prevalence of the pyrethroid target site resistance-associated gene mutation (refered to as kdr) and determine its frequency in pyrethroid-resistant horn populations in Brazil, a total of 1,804 horn flies of 37 different screened through a diagnostic polymerase chain reaction (PCR) assay which detects the presence or absence of the horn fly kdr mutation and is predictive of pyrethroid resistance. The kdr mutation was detected in 12.92% of the flies, of which 11.70% were heterozygous, possessing one mutated allele and one wild type (pyrethroid susceptible) allele, and 1.22% were homozygous for the mutated allele. When populations were grouped by region, data analysis indicated the Central-West populations, South populations and Southeast were isolated from one another and kdr occurrence seems to be an independent effect probably reflecting the insecticide strategy used by each ranch. Although resistance to pyrethroids is disseminated throughout Brazil, only 48% of resistant populations had kdr flies, and the frequency of kdr individuals in each of these resistant populations was quite low. But this study shows that, with the apparent exception of the Northeast region, the kdr mechanism associated with pyrethroid resistance occurs all over Brazil.

Technical Abstract: To investigate the kdr (knockdown resistance) resistance-associated gene mutation and determine its frequency in pyrethroid-resistant horn fly (Haematobia irritans) populations, a total of 1,804 horn flies of 37 different populations from all Brazilian regions (North, Northeast, Central-West, Southeast, and South) were molecular screened through polymerase chain reaction (PCR). The kdr gene was not detected in 87.08% of the flies. However, the gene was amplified in 12.92% of the flies, of which 11.70% were resistant heterozygous and 1.22% were resistant homozygous. Deviation from Hardy-Weinberg equilibrium (HWE) was found only in 1 ranch with an excess of heterozygous. When populations were grouped by region, three metapopulations showed significant deviations of HWE (Central-West population, South population and Southeast population). This indicates that populations are isolated one from another and kdr occurrence seems to be an independent effect probably reflecting the insecticide strategy used by each ranch. Although resistance to pyrethroids is disseminated throughout Brazil, only 48% of resistant populations had kdr flies, and the frequency of kdr individuals in each of these resistant populations was quite low. But this study shows that, with the apparent exception of the Northeast region, the kdr mechanism associated with pyrethroid resistance occurs all over Brazil.

Last Modified: 10/20/2014
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