Impacts of long-term insecticide treatment regimes on skdr and kdr pyrethroid resistance alleles in horn fly field populations
We evaluated the effects of four different 6-year duration control strategies on the resistance levels and frequency of the pyrethroid target site resistance alleles, superkdr (skdr) and kdr, at four field populations of Haematobia irritans irritans (Linnaeus, 1758) (Diptera: Muscidae) in Louisiana, USA. Consecutive use of pyrethroid ear tags for 6 years caused a significant increase in the resistance ratio to pyrethroids as well as the frequencies of both skdr and kdr resistance alleles. After 3 years of consecutive use of pyrethroid ear tags, followed by 1 year with no treatment, and followed by 2 years with organophosphate ear tags, the resistance ratio for pyrethroid was not significantly affected, the %R-skdr significantly dropped while the %R-kdr allele remained relatively high and stable. Similar results were observed when pyrethroid ear tags were used for three consecutive years, followed by 1 year with no treatment, and followed by 2 years with endosulfan ear tags; however, this treatment resulted in a slight increase in the resistance ratio for pyrethroids. In a mosaic, the resistance ratio for pyrethroids showed a 2.5-fold increase but the skdr-kdr genetic profiles did not change, as the %R alleles (skdr and kdr) remained low and stable through the 6 years. Lack of exposure to pyrethroid insecticides for 3 years significantly affected the skdr mutation but not the kdr mutation, preventing re-establishment of susceptibility to pyrethroids. SS-SR (skdr-kdr) individuals were responsible for the maintenance of the kdr mutation in two of the populations studied, and fitness cost seems to strongly affect the SR-RR genotype. None of the four treatment regimens evaluated in the study had satisfactory results for the management of kdr resistance alleles.
KeywordsHaematobia irritans Control Management Fitness cost Target site resistance
We wish to acknowledge the assistance of Michael Becker with fly collections and bioassays. LND acknowledges funding support from the National Council for Scientific and Technological Development (Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq), Brazil, and the Agricultural Research Services (ARS) Research Participation Program Agreement #60-3094-5-001 administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy (DOE) and the United States Department of Agriculture (USDA-ARS). ORISE is managed by Oak Ridge Associated Universities (ORAU) under DOE contract number DE-AC05-06OR23100. FDG acknowledges funding support from USDA-ARS Knipling-Bushland US Livestock Insects Research Laboratory CRIS project 3094-32000-036-00. USDA is an equal opportunity employer.
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Conflict of interest
The authors declare that they have no conflict of interest.
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