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

Abstract

Horn fly resistance to pyrethroid insecticides occurs throughout Brazil, but knowledge about the involved mechanisms is still in an incipient stage. This survey was aimed to identify the mechanisms of horn fly resistance to cypermethrin in Mato Grosso do Sul state, Brazil. Impregnated filter paper bioassays using cypermethrin, synergized or not with piperonyl butoxide (PBO) and triphenyl phosphate (TPP), were conducted from March 2004 to June 2005 in horn fly populations (n = 33) from all over the state. All populations were highly resistant to cypermethrin, with resistance factors (RF) ranging from 89.4 to 1,020.6. Polymerase chain reaction (PCR) assays to detect the knockdown resistance (kdr) mutation also were performed in 16 samples. The kdr mutation was found in 75% of the tested populations, mostly with relatively low frequencies (<20%), and was absent in some highly resistant populations. Addition of TPP did not significantly reduce the LC 50 in any population. However, PBO reduced LC 50 s above 40-fold in all tested populations, resulting in RFs ≤ 10 in most cases. Horn fly resistance to cypermethrin is widespread in the state, being primarily caused by an enhanced activity of P450 mono-oxygenases and secondarily by reduced target site sensitivity.Keywords: Horn fly, insecticide resistance, metabolic resistance, kdr. ResumoResistência da mosca-dos-chifres a inseticidas piretróides ocorre em todo o país, entretanto, o conhecimento sobre os mecanismos envolvidos é ainda incipiente. Este estudo objetivou identificar os mecanismos de resistência desta mosca à cipermetrina em Mato Grosso do Sul. Bioensaios utilizando papéis impregnados com cipermetrina, isoladamente ou sinergizada por butóxido de piperonila (PBO) ou trifenil fosfato (TPP), foram realizados de março/2004 a junho/2005 em 33 populações. Todas as populações apresentaram elevada resistência à cipermetrina, com fatores de resistência (FR) variando de 89,4 a 1.020,6. Ensaios de reação em cadeia da polimerase (PCR) visando a detecção de kdr ("knockdown resistance") foram realizados em 16 amostras. A mutação kdr foi detectada em 75% das populações, geralmente em baixas frequências (<20%) e ausente em algumas populações resistentes. A adição de TPP não reduziu significativamente a CL 50 em nenhuma população. Entretanto, o PBO reduziu em mais de 40 vezes a CL 50 de todas as populações testadas, resultando em FR ≤ 10 na maioria dos casos. Resistência da mosca-dos-chifres à cipermetrina encontra-se disseminada no estado, sendo causada primariamente por um aumento da atividade de P450 mono-oxigenases e secundariamente pela redução da sensibilidade do sítio de ação do inseticida.Palavras-chave: Mosca-dos-chifres, resistência a inseticidas, resistência metabólica, kdr.

Influence of selective treatment onHaematobia irritansinfestation of untreated cattle

“…Similar finding has been reported in pyrethroid-resistant horn fly populations 17,18,19 and the increased OP-susceptibility may result from an increased diazinon activation by mixed function oxidases 20 . High levels of horn fly pyrethroid resistance have been reported in Uruguay 21 and, although the involved mechanisms remain unknown, it is possible that mixed function oxidases play a relevant role in resistance to pyrethroids in horn fly populations from Uruguay as has been reported in Brazil 22 .…”

Identification of Sindhi cows that are susceptible or resistant to Haematobia irritans

“…Bulls have higher infestation rates than cows; therefore, selectively treating bulls in a breeding herd would be of value. However, it is important to evaluate the implications of selective treatment for the development of insecticide resistance (BARROS et al, 2013). Since information regarding the development of resistance in selective treatment programs involving long-lasting insecticides is lacking, it is important to perform bioassays before and after treatments to evaluate the susceptibility of horn fly populations to the drugs in use.…”

“…A forte concordância entre estes dois métodos sugere que as vacas susceptíveis podem ser identificadas pela contagem das moscas, o que permite estabelecer seleção dos animais resistentes ou tratamento ou eliminação dos mais susceptíveis. Horn fly resistance to pyrethroids, which are widely applied in Brazil (BARROS et al, 2013;BRITO et al, 2019), increases production costs and causes environmental contamination. Horn fly infestation of a herd is directly influenced by the proportion of susceptible animals in the herd (STEELMAN et al, 1993;JENSEN et al, 2004).…”

Pyrethroid and organophosphate pesticide resistance in field populations of horn fly in Brazil

“…Several authors have reported the presence of resistant horn fly populations in many tropical and subtropical areas of the globe (Harvey et al, ; Schmidt et al, ; Foil et al, ; Li et al, ; Temeyer et al, ; Sabatini et al, ; Barros et al, ; Domingues et al, ). The dose‐response bioassay has been considered the most precise method to assess the susceptibility of a population to a compound (Busvine, ; Finney, ), justifying the frequent use of this bioassay, by others (Barros et al, , , ; Guerrero & Barros, ) and our group, to monitoring resistance in horn fly populations. The LC 50 estimated from the filter paper bioassays and the resulting dose‐response curve is used to define the baseline susceptibility of a population (Miller et al, ).…”