Dynamics of cypermethrin resistance in the field in the horn fly, Haematobia irritans

Abstract

The toxicity of cypermethrin to the horn fly Haematobia irritans (L.) (Diptera: Muscidae) was determined for samples collected from untreated herds at a farm in central Argentina from October 1997 to May 2001. Field tests of the efficacy of cypermethrin against horn flies were first carried out at this farm in 1993, when the fly was shown to be susceptible to pyrethroids. Subsequently the horn fly populations on this farm were shown to have become resistant and, since 1997, the use of cypermethrin has been restricted to experimental purposes. In this study, fly samples collected in 1999, 2000 and 2001 were subjected to a polymerase chain reaction (PCR) to detect the presence of a specific nucleotide substitution in the sodium channel gene sequence, which has been associated with target site insensitivity to pyrethroids. This analysis showed that the level of cypermethrin resistance had diminished between 1997 and 2001. However, this was not sufficient to restore the efficacy of this pyrethroid to the level found prior to the onset of resistance. Heterozygous and homozygous resistant flies were detected in all samples of flies subjected to PCR diagnosis of alleles conferring target site resistance.

Survey of Resistance to Permethrin and Diazinon and the Use of a Multiplex Polymerase Chain Reaction Assay to Detect Resistance Alleles in the Horn Fly, <I>Haematobia irritans irritans</I> (L.)

“…The PCRbased genotyping technique has also been used to study Þeld dynamics of pyrethroid resistance in the horn ßy (Guerrero et al 2002, Guglielmone et al 2002. Our study established a positive correlation between overall kdr allelic frequency and permethrin resistance.…”

“…A polymerase chain reaction (PCR)-based technique has been developed to detect the kdr and super-kdr mutations in individual horn ßies . This technique has been successfully used to investigate Þeld dynamics of pyrethroid target sitebased resistance in horn ßies (Guerrero et al 2002, Guglielmone et al 2002.…”

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

“…Guglielmone et al (2002) found nearly 50% of kdr allelic frequency in a population treated with cypermethrin for years; this frequency dropped to 20% after no cypermethrin treatments during four years. Although LC 50 reduction followed a decrease in the kdr gene frequency from 121.6 to 5.8 ug.cm -2 , it was still eight times higher than the LC 50 from the Kerrville susceptible strain (GUGLIELMONE et al, 2001) and it was not enough to reestablish cypermethrin efficacy.…”

“…Interestingly, although resistance to pyrethroids is disseminated throughout Brazil, only 48% of the resistant populations had kdr flies and their frequency in resistant populations was quite low. Although low kdr frequency among resistant populations could be associated to fitness cost (SCOTT et al, 1997), Guglielmone et al (2002) found that fitness cost was not enough to control resistance spread, but only slowly reduce resistance when pyrethroids were not in use.…”

High Levels of Insecticide Resistance in Introduced Horn Fly (Diptera: Muscidae) Populations and Implications for Management

“…Target insensitivity has been reported as the primary mechanism of resistance to pyrethroids in horn ßy populations in the United States (Guerrero et al 2002), Mexico (Li et al 2003), and Argentina (Guglielmone et al 2002). This insensitivity is due to the presence of the knockdown resistance mutation kdr, which involves the change of a leucine residue by phenylalanine in the voltage-dependant sodium channel.…”