Comparison of Insecticidal Ear Tags and Ivermectin in a Topical Formulation For Controlling Horn Flies and Face Flies (Diptera: Muscidae) On Pastured Cattle!. 2

Ralph E. Williams and Cheryl A. Towell

Department. of Entomology, Purdue University West Lafayette, Indiana 47907

J. Agric. Entomol. 9(4):283·288 (OclobC!r 1992)

ABSTRACT A comparison was made of the clTicacy of insecticide­impregnated ear tags and a topical formulation of ivcr'mectin fol' controlling horn flies, flaematobia irrila,ns (L,), on pastured cattle. Observations were also made on control of face flies, Musca autumnalis De Geer. lvermeciin 0.5% w/v pour-on applied at 500 J.lglkg body weight was compared in one ll'ial to 10% pemlcthrin ear lags, and in another trial to 20% diazinon ear tags. In each trial, treatments consisted of a herd treated with ivermectin alone (initial treatment followed by a second treatment approximately 3 mo later), a herd treated only with an insecticide-imprebrnatcd ear tag, and a herd treated with ivcl'mectin llS in the first herd, but with an insccticide· impregnated ear tag installed in mid-summer. In the two herds treated with ivcrmectin alone, season-long horn Oy control of 48% and 84% was obtained. In the herds treated with insecticide car tugs, perrnethrin tags provided a 93% reduction in horn nics, and diazinon tags providcd a 90% reduciion in horn nics. In the two herds with the combination of ivcrmectin and insecticide-impregnated ear tags, horn fly contl"ol exceeded 90% in each. The only significant (P < 0.05) face fly control was observed in herds where calLIe were treated with pcrmethrin car tags, both alone and in combination with ivermeclin.

KEY WORDS f/aema.lobia irrilans, Musca aUlumnalis, ivcrmectin, permelhrin, diazinon, Diptera, Muscidae.

The horn ny, Haematobia irritans (L.), is generally considered as the single most important insect pest of range cattle in North America (Wright 1985). Since its introduction in the United States around 1885, many insecticides and treatment techniques have been used to control this pest (Drummond et al. 1988). A significant advance in the methods used to apply insecticides to cattle to control horn flies was the development of the insecticide-impregnated ear tag. In an early effort, Harvey and Brethour (1970) were able to control horn mes for 1 rno with identification ear tags equipped with resin strips containing dichlorvos.

In other studies, Ahrens (1977) controlled hom flies for 12 wk with stirofos­impregnated ear tags, and Ahrens and Cocke (1979) obtained a 100% reduction in horn flies for 20 wk using fen valerate-impregnated ear tags. Several

lCont.ribution from the Deportment of Entomology, JOllrnol Paper No. 13165, Purduc University, Aj,,'Ticultura1 Expcriment Stntion. Wcat Lafayctte, IN 47907.

2 Received far publication 24 August 1991; accepted 27 March 1992.

283

284 J. Agric. Entomol. Vol. 9, NO.4 (992)

insecticide ear tag fonnulations have since become commercially available for controlling horn flies. Recently, horn fly populations resistant to pyrethroid insecticides in ear tag formulations have been documented. The first published report of resistance in horn flies to pyrethroids was in Georgia (Sheppard 1984). Several states have confirmed horn fly populations resistant to pyrethroids and other insecticides. A comprehensive review of the resistance problem in horn flies is presented by Sparks et al. (1985).

The "pour-on" technique, developed to apply systemic insecticides topically to cattle to control cattle grubs, was first used to control horn flies by Rogoff and Kohler (1961). Good control was obtained when they poured toxaphene and crufomate along the backline of cattle. Others who have reported on the successful use of pourMons include Dorsey et al. (1962), using coumaphos, crufomate and trichlorfon; and Rogoff et al. (1963), using DDT and toxaphene.

As reported by Campbell et al. (1983), ivermectin (22, 23-dihydroavermectin B1) was effective in reducing nematode and arthropod populations of cattle when administered by subcutaneous and oral (drench) routes. The use of ivermectin in a topical formulation as an anthelmintic in cattle was reported by Jacobs et al. (1989), McKenna (1989), Bisset et al. (1990), and Taylor et al. (1990). Alva-Valdes et al. (1986) reported on the efficacy of ivermectin against both helminths and selected arthropods. They reported that ivermectin applied topically at 500 ~glkg was effective against cattle grubs, Hypoderma bouis (L.) and H. li"eatum (de Villers), and the cattle biting louse, Bouicola bouis (1.). Also, Barth and Preston (1988) reported that topical treatment with ivermectin at 500 ~g/kg was fully effective against Chorioptes bouis (Gerlach) and Sarcoptes scabiei (De Geer) on cattle.

In the study reported here, two trials were conducted to evaluate the efficacy of ivermectin in a pour-on formulation as compared to, and in conjunction with, insecticide-impregnated ear tags for controlling horn flies and face flies on pastured cattle.

Materials and Methods

Trial 1. This study was conducted at the ScholerMPurdue Farm in Warren County, Indiana. Crossbred Hereford and Angus cattle were split into four herds, each separated from other cattle by approximately 300-500 m. Herd 1 consisted of 21 yearling heifers plus 1 bull, and served as an untreated control. Herd 2 consisted of 24 cow/calf pairs plus 1 bull. All adult cows and the bull in this herd were treated with iverrnectin 0.5% w/v (weight/volume) pour-on (MSD AGVET, Rahway, New Jersey) at 500 ~g/kg body weight on 2 June 1988 followed by a second treatment to all animals in the herd on 30 August 1988. Ivermectin pourMon treatments were made by applying 95% of the material along the backHne from the withers to the tailhead. The remaining 5% was applied on the poll of each animal allowing material to flow down on the forehead in an attempt to control face flies, Musca autumnalis. Herd 3 consisted of 24 cow/calf pairs plus 1 bull. All adult cows and the bull in this herd were treated initially with ivennectin 0.5% w/v pour-on at 500 j.lg/kg body weight on 2 June 1988 as in Herd 2. On 13 July 1988 the same animals were treated with two 10% permethrin (Atroban®, Pitman-Moore, Inc., Kansas City,

285 WILLIAMS and TOWELL: Horn and Face Fly Control on Cattle

Kansas) ear tags each. On 30 August 1988, a second ivermectin treatment was made to both adult cows and calves, and all permethrin ear tags were removed. Herd 4 consisted of 65 cow/calf pairs plus 2 bulls. Each adult animal in this herd was treated with two 10% permethrin (Atroban) ear tags on 2 June 1988. These tags were kept on for the duration of the study.

The population of horn flies on the cattle was assessed weekly between 1000 and 1400 h by visual counts of flies on each of 10 randomly-selected adult cows in each herd. Counts consisted of estimates of the number of horn flies on one side from the top of the back to the belly, and from the point of the shoulder to the back leg of the animal during a 10-15 sec interval. Face fly populations were also assessed on the same animals by counting all face flies resting on the face and head of each animal during a 10-15 sec interval. Fly count data were statistically analyzed by a one-way analysis of variance, and means at each date were compared by the Duncan's multiple range test at the 5% level of significance (Little and Hills 1978).

Trial 2. This study was conducted at the Southern Indiana Purdue Agricultural Center (SIPAC) in Dubois County, IN. Crossbred Hereford, Angus and Simmental cattle were split into four herds, each separated from other cattle by approximately 300-500 m. Herd 1 consisted of 18 cow/calf pairs plus 1 bull, and served as an untreated control. Herd 2 consisted of 28 yearling heifers plus 1 bull. All animals in this herd were treated, as in Trial I, with ivermectin 0.5% w/v pour-on at 500 ~glkg body weight on 18 May 1988 and on 31 August 1988. Herd 3 consisted of 26 yearling heifers plus 1 bull. All animals in this herd were treated initially with ivermectin 0.5% wlv pour-on at 500 J.1g/kg body weight on 18 May 1988. On 19 July 1988, the same animals were treated with two 20% diazinon (Terminator®, Fermenta Animal Health, Kansas City, Missouri) ear tags each. On 31 August 1988, all animals in the herd received a second ivennectin treatment, and all diazinon ear tags were removed. Herd 4 consisted of 19 cow/calf pairs plus 1 bull. Each adult animal in this herd was treated with two 20% diazinon (Terminator) ear tags on 18 May 1988; tags were kept on for the duration of the study.

Fly counts and data analysis were done as in Trial 1, except fly counts were made every 2 wk.

Results and Discussion

Trial!. Horn fly control (percent reduction from untreated herd) averaged 84% on cattle in Herd 2 treated with the ivermectin pour-on, 91% on cattle in Herd 3 treated with the ivermectin pour~on and permethrin ear tags, and 93% on cattle in Herd 4 treated with permethrin ear tags only (Table 1). In both herds treated with the ivermectin pour-on, horn fly numbers never exceeded 16.5 flies per side as compared to as many as 190 flies per side on untreated animals. Although greater control over the course of the season was obtained from Herd 4 in which cattle were treated only with permethrin ear tags, horn fly numbers on cattle in all treated herds were maintained well below economic damaging levels of 200 flies per animal as established by Kunz et al. (984). Face fly populations were not affected by ivermectin treatments. In Herd 4, face

286 J. Agric. Entomol. Vol. 9, No. -1 (1992)

Table 1. Mean horn fly counts at Scholer-Purdue Farm (Trial 1 - 1988): X (mean percent reduction ft'om control).a,b

Treatment

Herd 3

Herd 2 (ivermectin pour~on + Herd 4

Date Herd 1

(control) (ivermectin

pour-on) permethrin ear tags)

(pennethrin ear tags)

May 31 June 15 June 24· July 1 July 9 July 15 July 22 July 28 Aug 3 Aug 12 Aug 20 Aug 27 Sept 3 Sept 11 Sept 25

12.1 ab 25.2 a 20.0 a 22.0 a 25.5 a 32.5 a

6.5 a 12.7 a 20.0 a 52.7 a

162.5 a 190.0 a

43.5 a 49.5 a 55.0 a

4.9 c 10.0 b (60)"

6.2 bc(69) 5.8 b (74) 7.1 b (72) 5.0 b (85) 6.3 a (3) 3.6 b (72) 4.7 b (77) 7.0 b (87)

16.0 b (90) 13.3 b (93) 16.0 b (63)"

4.3 b (91) 16.5 b (70)

11.0 b 8.8 b (65)< 7.4 b (63) 3.1 bC(86) 4.8 bc(81) 0.4 c (99)</

ob (100) 1.3 c (90) 2.3 c (89) 4.8 b (91)

10.5 b (94) 12.0 b (94)

7.5 bc(84j' 2.5 b (95) 2.9 c (95)

16.9 a 6.9 b(73)<" 3.0 c(85) 1.7 c(92) 1.5 c(94) 0.3 c(99) 0.2 b(97) 1.2 c(91) 1.7 c(92) 4.8 b(91) 4.7 b(97) 6.3 b(97) 4.9 c(89) 1.0 b(98) 0.8 c(99)

X 48.9 a 8.2 b (84) 4.6 b (91) 3.3 c(93)

" Means within TOWS followed by the SDme letter are not significantly different <P < 0.05) (Duncan's multiple range test, Little and Hills 1978),

b Counts represent means of horn flies counted on one side of 10 animals in each herd. c Ivermedin treatment (500 Ilglkg) - June 2, August 30. " Ear tags applied July 13. • Ear tags applied June 2.

fly control averaged 61% for the duration of the study; in Herd 3, 31%. During the time permethrin tags were on the cattle in Herd 3 (13 July - 30 August), face fly control averaged 55%.

Trial 2. Horn fly control (percent reduction from untreated herd) averaged 48% on cattle in Herd 2 treated with the ivermectin pour-on only, 93% on cattle in Herd 3 treated with the ivermectin pour-on and diazinon ear tags and 90% on cattle in Herd 4 treated with diazinon ear tags only (Table 2). In all of these herds, the population means of horn fly were less than 60 per head, well below the economic damaging levels of 200 flies per animal (Kunz et al. 1984). No significant (P > 0.05) face fly control was achieved in any of the treated herds.

The ivermectin pour-on treatment used was effective in significantly (P < 0.05) reducing horn fly populations. The second treatment was needed to keep horn fly numbers below the 200 flies per animal level, especially at SIPAC. At

287 WILLIAMS and TOWELL: Horn and Face Fly Control on Cattle

Table 2. Mean horn fly counts at SIPAC (Trial 2 - 1988): X (mean percent reduction from control).a.b

Treatment

Herd 3 (ivermectin

Herd 2 pour-on + Herd4 Herd 1 (ivermectin diazinon (diazinon

Date (control) pour-on) ear tags) ear tags)

May 17 27.5 b -' -' 49.0 a June 4 54.5 a 0 b(100) 0 b (l00) 4.0 b(93'" June 16 187.5 a 10.0 a(95) 11.5 a (94) 1.0 b(lOO) June 28 66.0 a 15.0 b(77) 39.5 ab(40) 0 b(lOO) July 14 63.3 a 41.0 b(35) 10.9 c (83) 1.8 e(97) July 29 70.0 a 42.0 b(40) 5.0 e (93)" 14.00(80) Aug 10 112.5 b 232.5 a(O) 0.6 e (100) 12.5 c(89) Aug 25 194.0 a 188.0 a(3) 0 b (l00) 4.5 b(98) Sept 11 270.0 a 7.5 b(99Jd 0 b (l00)" 17.0 b(94) Sept 28 71.5 a 70.5 a(5) 18.0 b (76) 28.0 b(62)

X 104.9 a 55.1 b(48) 7.8 e (93) 10.7 e(90)

" Means within rows followed by the .!lame letter are not significantly different (P < 0.05) (Duncan's multiple range lest, Little and Hill 1978).

h Counts represent means of horn nies counted 011 one side of 10 animal!; in each herd. ~ No counts made. oIlvcrrnectin treatment (500 ~glkg) - May 18, August 31. t Enr t.tlgs applied July 19. r Eur tags applied May 18.

SIPAC, each ivermectin treatment appeared to control horn fly populations for up to 4 wk.

Both insecticide-impregnated ear tag treatments were effective in controlling horn flies. However, as previously reported, populations of horn flies resistant to insecticides in ear tag formulations have been occurring, especially in situations l,vhere the same 01' related insecticides have been used on herds for 2 or more years. At SIPAC, pyrethroid resistance has been documented since 1986 (R. E. W., unpublished data). The lvermectin pour-on, as evaluated in these trials, shows promise as an alternative treatment for horn nies. even when it is used by itself. However, the pour-Oil formulation does not appear to be suitable for controlling face flies. One reason could be because of the systemic absorption of iverrnectin, which allows exposure only to blood-sucking nies.

288 J. Agrie. Enlomol. Vol. 9, No.4 (1992)

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