|Alison, Jr, M - LSU RES STAT WINNSBORO LA|
|Foil, Lane - LSU BATON ROUGE LA|
Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 5, 2002
Publication Date: July 11, 2002
Citation: GUERRERO, F., ALISON, JR, M.W., KAMMLAH, D.M., FOIL, L.D. USE OF THE POLYMERASE CHAIN REACTION TO INVESTIGATE THE DYNAMICS OF PYRETHROID RESISTANCE IN HAEMATOBIA IRRITANS IRRITANS (DIPTERA: MUSCIDAE). JOURNAL OF MEDICAL ENTOMOLOGY. 2002. v. 39. p. 747-754. Interpretive Summary: A pyrethroid resistant horn fly population in Louisiana was studied from 1991-1997. The flies were feeding on cattle which had received synergized pyrethroid ear tags in 1991, 1993, 1995, and 1997 and OP ear tags in 1992, 1994, and 1996. The resistance level of the fly population was analyzed by weekly fly counts, filter paper bioassays before and after tagging, and diagnostic PCR for the presence of pyrethroid resistance-associated gene mutations. Fly control during the first year of the study was poor, as the pyrethroid ear tags failed after only 7 weeks. The following year, OP ear tags controlled flies for 15 weeks. However, during the third year of the study, when pyrethroid ear tags were used again, fly control lasted only 6 weeks. Surprisingly, in year 4, when OP ear tags were used again, fly control dropped to only 4 weeks. Fly control remained poor for the rest of the study, lasting only 4, 3, and 2 weeks in 1995, 1996 and 1997, respectively. The gene mutation studies showed that there were very few female flies which did not possess at least one pyrethroid resistance-associated gene mutation. In fact, most of the post-tagging samples showed that less than 10% of the female flies had a pyrethroid susceptible (non-mutated) form of the gene. In the absence of pyrethroid pressure, the pyrethroid susceptible gene form is favored, and thus selected for, during the interval between the removal of pyrethroid ear tags in the fall and the resumption of pyrethroid tagging in the spring of the second year following. Unfortunately, the % of flies that contain only the susceptible gene form never exceeds 19% and pyrethroid control was never reestablished.
Technical Abstract: From 1991 through 1997, a field study was conducted to evaluate the use of pyrethroid and OP ear tags, alternated yearly, for the control of a pyrethroid resistant horn fly population in Louisiana. Fly resistance 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. Fly control in the first study year was poor, as pyrethroid ear tags were effective for only 7 weeks. The following year, OP ear tags provided 15 weeks of fly control. However, in all subsequent years, fly control was poor with both types of ear tags. The PCR assays showed that there were very few female flies which were homozygous for the pyrethroid susceptible sodium channel allele, never rising above 10% of the total females in the population. A fitness cost appeared to be associated with the pyrethroid resistant allele, as the resistant form was selected against in the absence of pyrethroid pressure. Despite the selection for the susceptible allele, the percentage of homozygous susceptible flies never reached over 19% of the population.