SHORT COMMUNICATION Susceptibility of irritans (Diptera: ) to Permethrin in Dairies in Aguascalientes, Mexico

CARLOS CRUZ-VA´ ZQUEZ, GUICELDA ALTAMIRA, MIGUEL RAMOS, LETICIA MEDINA, 1 2 ZEFERINO GARCIA-VAZQUEZ, AND JOHN GEORGE

Instituto Tecnologico Agropecuario de Aguascalientes, AP 74-2, Admon, Postal No. 2, CP 20041, Aguascalientes, Ags., Mexico

J. Med. Entomol. 39(6): 939Ð941 (2002) ABSTRACT The purpose of this study was to conduct a survey for the susceptibility of the horn ßy, Hematobia irritans (L.), populations to permethrin on dairy from Aguascalientes, Mexico. Samples of populations of horn ßies at 25 dairies were exposed to two discriminating doses (2.5 and 6.0 ␮g/cm2) on permethrin-treated Þlter papers and the percentage of mortality was compared with that of a susceptible strain treated with same doses of permethrin. The results show that there was a difference in the mortality from two discriminating doses and the mortality of the susceptible strain. Therefore, horn ßy populations at all dairies tested in Aguascalientes, Mexico, were susceptible to permethrin. This insecticide, as well as other , could continue to be used to provide satisfactory control of horn ßies in the study region.

KEY WORDS Hematobia irritans, susceptibility, dairy herd, Mexico

THE HORN , Hematobia irritans (L.), is an important control ßies on cattle, farmers depend on the intensive bloodsucking pest of cattle and is widely distributed in use of 5% permethrin applied as a pour-on at a dosage cattle-producing areas throughout North and Latin of 50 ml per cow at Ϸ80% of the dairies, or it is sprayed America (Foil and Hogsette 1994, Guglielmone et al. in pour-on solution, although that method of applica- 1997). Horn ßy control is based primarily on the use tion is not recommended by the drug company. At of insecticides to treat ßy-infested cattle. Insecticide Ϸ20% of dairies it is applied at a dosage of 40 ml per resistance to pyrethroids has been reported fromsev- cow using a back-pack hand-pump sprayer. Intervals eral regions of the world, including the United States, between applications are generally 15Ð20 d with ap- Canada, Mexico, and Argentina (Kunz and Kemp plications beginning in early June and ending in late 1994, Guglielmone et al. 1998) and is a major hin- September or early October. There are general four to drance to efforts to limit the adverse economic impact 12 treatments per season, depending on the abun- of these ectoparasites on cattle production. dance of ßies and the ownerÕs perception of when Horn ßy populations in northeastern Mexico have cows need treatment. Permethrin has been used in this been reported to be resistant to pyrethroids and have region for Ͼ12 yr, but during the past 6 yr it has been also been identiÞed in other regions south along the used more intensively; and some milk producers have Gulf of Mexico and west to the PaciÞc coast (Kunz et reported control failures. It is important to note that al. 1995, Santamarõ´a et al. 1995). The State of Aguas- this region is free of Boophilus , therefore per- calientes in north central Mexico is an important milk methrin has only been used to control biting ßies. production center with the majority of dairies con- This study was conducted to assess the degree of centrated in four counties, where there are Ϸ36,800 susceptibility to permethrin of horn ßy populations on cows in 210 dairies. The horn ßy is widely distributed dairy cattle in Aguascalientes, Mexico. in the region and is an important pest. The conÞne- ment conditions and manure management system in Materials and Methods the dairies could be suitable for development of this parasite, but ßies also breed on cattle and in manure Twenty-Þve dairies in Aguascalientes that had a in pastures adjacent to the dairies and migrate to the history of making 10Ð12 applications of permethrin dairy cows (Cruz-Va´zquez et al. 1999). In attempts to per year were selected as sites for sampling horn ßies and conducting discriminating dose mortality tests. All of the dairies selected for the study maintained their 1 Cenid-Parasitologõ´a Veterinaria (INIFAP-SAGAR), AP 206 CI- VAC, CP 62500, Jiutepec, Mor., Mexico. cows in a conÞnement system referred to as “free 2 Knipling-Bushland U.S. Livestock Research Laboratory, conÞnement in open corrals.” This systemconsisted of USDAÐARS, 2700 Fredericksburg Road, Kerrville, TX 78028. pens with a soil ßoor and shaded area. A cement ßoor

0022-2585/02/0939Ð0941$02.00/0 ᭧ 2002 Entomological Society of America 940 JOURNAL OF MEDICAL ENTOMOLOGY Vol. 39, no. 6

Table 1. Summary of a dose mortlity analysis of an insecticide Table 2. Percentage mortality of horn flies exposed to per- susceptible in vitro colony of horn flies at Kerrville, TX methrin from 25 dairies in Aguascalientes, Mexico

LC 95% CL LC 95% CL Slope SE ␹2 Dose 50 99 County/dairy Control ␮ 2 ␮ 2 2.63 2.30Ð2.88 5.94 4.85Ð9.08 6.56 Ϯ0.441 77.39 2.5 g/cm 6.0 g/cm Aguascalientes The Þlter paper assay (Sheppard and Hinkle 1987) was replicated 1 1.6 60 100 three times. 2 0 70 100 3 0 65 100 4 0 60 100 was located along a feed bunk and water dispenser. 5 1.6 65 100 Approximately 40Ð50 Holsteins per corral were con- 6 0 65 100 Jesu´ s Maria Þned together in this manner. This allowed each cow 1 1.6 60 100 2 2 Ϸ45 m of corral space and 3.7 m of shade. 2 0 65 100 Horn ßies adults were exposed to permethrin 3 1.6 60 100 treated Þlter papers (Sheppard and Hinkle 1987) with 4 0 70 100 ␮ 2 5 0 70 100 two discriminating doses of permethrin (2.5 g/cm 6 0 65 100 2 and 6.0 ␮g/cm ) using acetone as the diluent. Dis- San Francisco 1 1.6 65 100 crimminating doses represented the LC50 and LC99 values fromreplicated dose-mortalityanalyses (Table 2 1.6 70 100 3 0 60 100 1) of the insecticide susceptible in vitro horn ßy col- 4 0 65 100 ony maintained at the Knipling-Bushland U.S. Live- 5 0 65 100 stock Insects Research Laboratory in Kerrville, TX. 6 0 70 100 Treated Þlter papers (9-cm-diameter Whatman grade 7 0 60 100 Pabellon 1, Whatman, Hillsboro, OR) were prepared by apply- 1 1.6 65 100 ing 1 ml of the appropriate concentration of per- 2 0 60 100 methrin to each paper, which were then air dried, 3 1.6 65 100 wrapped in aluminum foil packets, and stored at 4ЊC 4 0 60 100 5 0 65 100 until used in tests with no more than 48 h between the 6 0 70 100 preparation of treated papers and testing. Susceptible straina 0 50 100 Each dairy was visited during August to October 1999 and horn ßies were collected directly fromthe a Mortality recorded in the susceptible laboratory strain of USDA- cows with a sweep net and transferred to a 1-liter ARS Research Laboratory, Kerrville, TX. holding cage made of clear plastic, as described by Kunz et al. (1995). When the cage contained Ϸ250Ð 300 ßies for a test, it was taken immediately to a nearby tween the degree of mortality observed for horn ßies shaded site where ßies were transferred to a plastic treated with the two discriminating doses (F ϭ petri dish in which a Þlter paper treated with per- 13,416.87; df ϭ 2, 23, 25; P ϭ 0.0001). The mean mor- methrin had previously been placed. Tests were per- tality of 64.6% of horn ßies exposed to the LC50 dose formed at the collection site throughout the day at of permethrin and of 100% for ßies exposed to the LC99 ambient temperatures that ranged from 21 to 24ЊC. dose is evidence of the absence of resistance to this were exposed to treated papers within 15Ð20 min chemical in the ßies on the dairy cattle (Table 2). of capture. Unsexed horn ßies of mixed ages (20 for Concerns expressed by milk producers about un- each petri dish) were placed into petri dishes accord- satisfactory results obtained with permethrin treat- ing to the criteria of Schmidt et al. (1985). Each treat- ments could be due to factors such as the application ment consisted of three replicates including a control of an inadequate volume or concentration of the prod- (Þlter papers treated with acetone). Mortality was uct. Because the horn ßy infestations on the conÞned recorded 2 h after horn ßies were placed into petri dairy cows resulted mainly from the migration of ßies dish. Each treatment was adjusted for nonspeciÞc emerging from manure of cattle in pastures adjacent mortality among the untreated controls using AbbottÕs to the dairies, treatments of permethrin applied to the formula (1925). dairy cattle would only impact adult ßies on the cattle Data were analyzed by one-way analysis of variance at the time of treatment and while lethal amounts of and the Student-Newman-Keuls mean separation test residual insecticide remained on the . Any at P Ͻ 0.05 (Scheffe´ 1953), using a randomdesign in female horn ßies that survived the exposure to per- which there were three treatments (control, 2.5 and methrin would probabily oviposit in fresh manure 6.0 ␮g/cm2) with three replicates for each dairy (Steel dropped by the cows in the corrals where they main- and Torrie 1988). tained. With the high concentration of cows in the corrals, any of the manure pats containing eggs and developing horn ßy larvae would be unlikely to remain Results and Discussion intact long enough for the completion of the devel- Results fromthis study indicate that horn ßy pop- opment of larvae to pupae. Under these circumstances ulations at all dairies were susceptible to permethrin. intensive use of permethrin on dairy cattle would not There was a statistically signiÞcant difference be- inßuence the rate of selection for insecticide resis- November 2002 CRUZ-VA´ ZQUEZ ET AL.: SUSCEPTIBILITY OF H. irritans TO PERMETHRIN 941 tance in a local horn ßy population breeding on pas- cently infested region of central Argentina. Bull. Ento- tured cattle. mol. Res. 87: 55Ð59. We conclude that H. irritans control should be done Guglielmone, A. A., S. E. Kunz, M. M. Volpogni, O. S. An- on the bases of regional strategic control to reduce the ziani, and S. G. Flores. 1998. Diagno´stico de poblaciones dairy farminfestation fromneighbors range cattle de la (Diptera:Muscidae) resistentes farms. The health authorities must be aware a cipermetrina en Santa Fe, Argentina. Rev. Med. Vet. and employement ßy control programs to decrease ßy (Buenos Aires) 79: 353Ð356. Kunz, S. E., and D. H. Kemp. 1994. Insecticides and acari- populations. cides: Resistance and environmental impact. Rev. Sci. Tech. Off. Int. Epiz. 13: 1249Ð1286. Acknowledgments Kunz, S. E., M. Ortiz, and H. Fragoso. 1995. Status of Haema- tobia irritans (Diptera:Muscidae) insecticide resistance We acknowledge the assistance of Diane Kammlah in northeastern Mexico. J. Med. Entomol. 32: 726Ð729. (USDA-ARS, Knipling-Bushland U.S. Livestock Insects Re- Santamarı´a, V.M.M. Ortiz, R. Franco, H. Fragoso, and J. search Laboratory, Kerrville, TX) in conducting this study. Osorio. 1995. Evaluacio´n biolo´gica de mosquicidas para We also thank the milk producers from Aguascalientes, Mex- el control de Haematobia irritans en Me´xico y situacio´n ico, for their cooperation. This study was supported by Cos- actual de la resistencia, pp. 119Ð123. In Memorias del III net-SEP (Mexico), Project 605.98-P Seminario Internacional de Parasitologõ´a Animal. Acap- ulco, Gro., Mexico. References Cited Scheffe´, H. A. 1953. A method for judging all contrast in the analysis of variance. Biometrika 40: 87Ð104. Abbott, W. S. 1925. A method of computing the effective- Schmidt, C. D., S. E. Kunz, H. D. Petersen, and J. L. Roberts. ness of an insecticide. J. Econ. Entomol. 18: 265Ð267. 1985. Resistance of horn ßies (Diptera: Muscidae) to Cruz-Va´zquez, C., I. Vitela, M. Ramos, M. T. Quintero, and permethrin and fenvalerate. J. Econ. Entomol. 78: 402Ð Z. Garcı´a-Vazquez. 1999. Presencia de Haematobia irri- 406. tans (L.) (Diptera:Muscidae) en ganado lechero estabu- Sheppard, D. C., and N. C. Hinkle. 1987. A Þeld procedure lado de Aguascalientes, Me´xico: Informe preliminar. Vet. using disposable materials to evaluate horn ßy insecticide Mex. 30: 205Ð208. resistance. J. Agric. Entomol. 4: 87Ð89. Foil, L. D., and J. A. Hogsette. 1994. Biology and control of Steel, R.G.D., and J. H. Torrie. 1988. Bioestadistica, prin- tabanids, stable ßies and horn ßies. Rev. Sci. Tech. Off. Int. cipios y procedimientos. McGraw-Hill, Mexico DF. Epiz. 13: 1125Ð1158. Guglielmone, A. A., O. S. Anziani, A. J. Mangold, R. E. Giorgi, M. M. Volpogni, and S. G. Flores. 1997. Seasonal varia- Received for publication 17 September 2001; accepted 17 tion of Haematobia irritans (Diptera:Muscidae) in a re- May 2002.