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United States Department of Agriculture

Agricultural Research Service

Title: ASSOCIATION OF THE KDR AND SUPERKDR SODIUM CHANNEL MUTATIONS WITH RESISTANCE TO PYRETHROIDS IN LOUISIANA POPULATIONS OF THE HORN FLY, HAEMATOBIA IRRITANS IRRITANS (L.)

Authors
item Foil, Lane - LSU, BATON ROUGE LA
item GUERRERO, FELIX
item Alison, M - LSU, WINNSBORO LA
item Kimball, Millard - LSU, WINNSBORO LA

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 12, 2004
Publication Date: April 20, 2005
Citation: Foil, L.D., Guerrero, F., Alison, M.W., Kimball, M. 2005. Association of the kdr and superkdr sodium channel mutations with resistance to pyrethroids in Louisiana populations of the horn fly, Haematobia irritans irritans (L.). Veterinary Parasitology. 129:149-158.

Interpretive Summary: Pyrethroid resistance has become a common problem in horn flies populations of Louisiana. A major cause of resistance is caused by mutations generated in the pesticide's target site leading to reduced product effectiveness. Pyrethroids target the sodium channel of cell membranes in arthropods. Pyrethroid resistance in three horn fly populations in Louisiana was monitored by weekly fly counts, filter paper bioassays and diagnostic DNA assays for the presence of pyrethroid resistance-associated mutations in the sodium channel gene coding region. The DNA assay tests for the kdr and superkdr sodium channel mutations which have been well established to lead to pyrethroid resistance in horn flies and other insects. This assay was used to determine the frequency of the target site insensitivity mechanism in the populations of horn flies which possessed varying degrees of insecticide resistance. The bioassays and the DNA assays were relative predictors of the fly control (zero to eight weeks of control) subsequently observed. Flies exposed to filter paper impregnated with a discriminating dose of one of 4 different insecticides were collected when 50% mortality was estimated. The DNA assay was performed on both the survivors and dead individuals from the filter paper assay. The results of the DNA assays indicated that the presence of the kdr mutation determined whether the flies could survive pyrethroid exposure. The kdr mutation had no effect on survival of exposure to diazinon or doramectin pesticides. Various combinations of kdr and superkdr mutations in individual flies were tested for their effect on survival of pyrethroid exposure. It was found that the pyrethroid resistance of a population increases as the abundance of the kdr mutation in a population increases. Horn flies without the kdr mutation were quickly killed by pyrethroids. The superkdr is not found in the absence of the kdr mutation and acts to increase the pyrethroid resistance of individuals which already possess the kdr mutation.

Technical Abstract: Pyrethroid resistance in three horn fly populations in Louisiana was monitored by weekly fly counts, filter paper bioassays and diagnostic PCR assays for the presence of pyrethroid resistance-associated mutations in the sodium channel gene coding region. The PCR assay for the kdr and superkdr sodium channel mutations was used to determine the frequency of the target site insensitivity mechanism in the populations of horn flies which possessed varying degrees of insecticide resistance. The bioassays and frequency of homozygous resistant kdr genotypes were relative predictors of the fly control (zero to eight weeks of control) subsequently observed. Flies exposed to filter paper impregnated with a discriminating dose of one of 4 different insecticides were collected when 50% mortality was estimated. Genotypes for the dead flies and the survivors were determined by the PCR assay. The results of the PCR assays indicated that the genotype at the kdr locus of the flies exposed to the two pyrethroids had an effect upon whether the flies were considered to be alive or dead at the time of collection. The kdr genotype of flies exposed to either diazinon or doramectin was unrelated to whether the flies were considered to be alive or dead, except for a single comparison of flies exposed to diazinon. When possible interactions of the kdr and superkdr mutations were compared, we found that there were no associations with the response to diazinon and doramectin. For one location, there were no survivors of the 75 flies with the SS-SS (superkdr-kdr) homozygous susceptible wild type genotype exposed to pyrethroids, while there were survivors in all of the other 5 genotypes. The SS-RR genotype flies were more susceptible to the pyrethroids than the SR-RR flies, but that was not the case for exposure to diazinon or doramectin. In the St Joseph population, there was an adequate number of flies to demonstrate that the SS-SR genotype was more susceptible to pyrethroids than the SS-RR and that flies with the SR-SR genotype were more susceptible to pyrethroids than the flies with the SR-RR genotype.

Last Modified: 8/27/2014
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