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

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.Keywords: Haematobia irritans, horn fly, resistance, pyrethroid. ResumoCom o objetivo de verificar a ocorrência e determinar a frequência da mutação kdr (knock down resistance) em populações de Haematobia irritans (mosca-dos-chifres) resistentes aos piretróides, foram analisados 1.804 indivíduos de 37 populações de todas as Regiões do Brasil. Com exceção da Região Nordeste, o kdr (knock down resistance gene) foi encontrado em populações de todas as regiões. A mutação não foi detectada em 87,08% dos indivíduos. Entretanto, o gene foi amplificado de 12,92% das moscas, das quais 11,70% se mostraram heterozigotas resistentes e 1,22% homozigotas resistentes. Em todas as populações verificou-se equilíbrio de acordo com a Lei de Hardy e Weinberg, exceto uma com excesso de heterozigotos. Entretanto, quando agrupamos diferentes populações numa metapopulação de acordo com a região geográfica, é possível observar um desvio nas populações Centro-Oeste, Sul e Sudeste, indicando isolamento populacional e que a ocorrência do kdr é provavelmente um efeito independente, talvez refletindo a estratégia de uso do inseticida de cada produtor. Apesar da resistência aos piretróides estar disseminada por todo o país, apenas 48% das populações resistentes apresentaram o kdr, e a frequência de indivíduos kdr nas populações resistentes se mostrou bastante baixa. À exceção da Região Nordeste, o mecanismo de resistência ligado ao kdr ocorre em todo o país.

Susceptibility of the horn fly, Haematobia irritans irritans (Diptera: Muscidae), to insecticides in Brazil

“…Flies survived twice the permethrin DC for 2 hours or even longer in most populations with survival rates greater than 1%, while no fly survived higher concentrations or longer exposures when the frequency of resistant individuals was lower than 1% (BARROS et al, 2007). Molecular analysis on some of these sampled populations confirmed that kdr (knockdown resistance) pyrethroid-resistant flies (SABATINI et al, 2009) were present in populations with permethrin RR as low as 1.5.…”

“…Such negative cross-resistance has previously been reported in horn fly pyrethroid-resistant populations (SHEPPARD; MARCHIONDO, 1987;CROSBY et al, 1991), caused by increased diazinon activation by the mixed function oxidases (MFOs) that are present in pyrethroid-resistant flies (CILEK et al 1995). In fact, MFOs play the most important role in horn fly pyrethroid resistance in Brazil (ATM Barros, unpublished data), although kdr has been detected at low frequencies in pyrethroid-resistant populations (GUERRERO; SABATINI et al, 2009). The relatively low use of OP products for controlling horn flies, as well as the widespread pyrethroid resistance mainly due to oxidative metabolism, may explain the high OP susceptibility.…”

“…Although presence of flies surviving a given DC may indicate resistance development in a population, it should not be directly associated with control failure unless correlation between bioassay (2003,2004). …”

“…Not all fly populations were bioassayed with both pyrethroids; populations were considered to be pyrethroid-resistant when analysis of either permethrin or cypermethrin bioassay data led to this conclusion. [1][2][3][4][5][6] Locations from where partial results from this study have previously been published: Braga and Barros (2003,2004).…”

Mechanisms of pyrethroid resistance inHaematobia irritans (Muscidae) from Mato Grosso do Sul state, Brazil

“…The kdr is already known in Brazilian pyrethroid-resistant horn fly populations (GUERRERO; BARROS, 2006;SABATINI et al, 2009), but little is known about its real importance and the role played by metabolic mechanisms.…”