Moxidectin Evaluation Against Solenoptes capillatus (Anoplura: Linognathidae)~ Bovicola bovis (Mallophaga: Trichodectidae)~ and Musca autumnalis (Diptera: Muscidae) on Cattle J.
D. WEBB,
J.
G. BURG, AND F. W. KNAPP
Department of Entomology, University of Kentucky, Lexington, Kentucky 40546
KEY WORDS Insecta, little blue cattle louse, cattle biting louse, systemic insecticide
INFESTATIONS OF lice and face flies, Musca autumnalis De Geer, cause an estimated annual loss of $126 and $52 million, respectively, to the U.S. cattle industry (Drummond 1987). Two common lice species on cattle, Solenoptes capillatus (Enderlein) and Bovicola hovis (L.), have been associated with weight loss, hair damage, and animal irritation. Calves infested with S. capillatus and Linognathus vituli (L.) lost more weight and had lower packed cell volume and hemoglobin measurements during the peak infestation period than un infested calves (Cummins & Graham 1982). One heavily infested heifer lost significant weight even though milk production was not affected (Cummins & Graham 1982). Heavy infestations of B. hovis may result in hair loss from scratching by irritated animals, and lesions may occur at the sites of feeding lice colonies (Butler 1985). M. autumnalis adults do not directly affect weight gain in cattle; however, adult flies have been implicated in the spread of pinkeye and the transmission of eye worms (Thelazia spp.) (Wright 1985). Current methods used for cattle lice control include whole-body dips, powders, sprays, and pourons; for M. autumnalis, treatments include sprays, wipe-on insecticides, dust bags, and feed-through insecticides (Wright 1985). Although these methods provide some control, they are not completely effective and often require multiple applications (Wright 1985, Titchener 1985). S. capillatus was
controlIed for up to 28 d with a single injection of ivermectin (Strong & Brown 1987); however, reinfestation may occur after ivermectin levels have subsided. A slow-release bolus that contains a systemic parasiticide is one method for delivering a prolonged, effective level of treatment to host animals. Slow-release ivermectin formulations are effective in the control of several multi host tick species on cattle (Soli et aI. 1989). Not only does this method provide systemic levels of insecticide in the host blood, but the insecticide may also be excreted in the feces and provide control of manure breeding parasites. Bolus formulations that release 50 ~g/kg of ivermectin per day were lethal to Haematobia irritans (L.) larvae in cattle feces (Wall & Strong 1987). Bolus formulations of diflubenzuron (Miller 1974, Wright 1975, Miller et aI. 1986, Webb et aI. 1989, Miller et aI. 1990) and methoprene (Miller et aI. 1979) have been used to control larval H. irritans and M. autumnalis. Our study was done to determine the effectiveness of moxidectin, a compound with ivermectinlike activity, in controlled-release bolus and injectable formulations for the control of S. capillatus and B. havis on rangeland beef cattle. In addition, the level and persistence of moxidectin activity in cattle feces was determined against M. autumnalis larvae.
, (AmericanCyanamidCL301423), AmericanCyanamidCompany,P.O.Box400,Princeton,N.J.08540.
Twenty-five beef cattle (1l0-320 kg, mixed breed and sex) were randomly assigned to five experi-
Materials and Methods
0022-0493/91/1266-1269$02.00/0 © 1991Entomological Societyof America
Downloaded from http://jee.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2016
J. Econ.Entomol.84(4):1266-1269(1991) ABSTRACT Slow release formulations of 375, 750, and 1,125 mg (AI) in 50-g boluses and a subcutaneous injectable formulation (0.2 mg AI/kg body wt) of moxidectin (CL30l423) were tested for the control of the little blue cattle louse, Solenoptes capillatus (Enderlein), and the cattle biting louse, Bovicola bovis (L). S. capillatus populations were reduced 4 wk after treatment and complete control was observed 6 wk after treatment in groups treated with boluses. B. bovis were first observed at 3 wk and continued to increase throughout the 14-wk te~t period. These were experimental boluses and future boluses may perform differently. Subcutaneous injections of moxidectin gave complete control of S. capillatus for a 27d test period. Feces from animals treated with boluseswere tested with face fly larvae, Musca autumnalis De Geer, to demonstrate fecal activity of moxidectin. Larval mortality in these groups ranged from 90 to 30% from 2 d to 10 wk after treatment.
August 1991
WEBB
ET AL.: MOXIDECTIN
AGAINST
CATTLE
LICE
AND FACE
1267
FLIES
Table 1. No. (£ ± SEM) or S. capillatua (x 10) on callie boluscd with a 50-g bolus per animal containing 375, 750, or 1,150 mg (AI) or moxidectio Wk after treatment"
Treatment
n
Control 375 750 1,125
4 5 4 5
0 160 66 18 96
± ± ± ±
2 17a 19ab 6b 50ab
280 ± 22 ± 5± O±
58a 20b 5b Ob
100 ± 96 ± 2± 18 ±
36a 62a 2b llb
4
6
8
88 ± 12a 14 ± 12b Ob O± 120 ± 120b
62 ± 40a O± Ob O± Ob O± Ob
8 o o o
± ± ± ±
10 Sa Ob Ob Ob
8 o o o
± ± ± ±
Sa Ob Ob Ob
12 15 o o o
± ± ± ±
14 5a Ob Ob ob
10 o o o
± ± ± ±
4a Ob Ob ob
mental groups of five animals each. Before treatment, all animals were weighed and identified with numbered ear tags. One group of animals was used as an untreated control and animals in three groups each received a 50-g bolus containing 375, 750, or 1,125 mg (AI) moxidectin (American Cyanamid Company, Princeton, N.J.). Boluses were administered with a balling gun and the animals were observed for bolus retention. The number of S. capillatus and B. bovis per animal was assessed at day 0 and at 1, 2, 4, 6, 8, 10, 12, and 14 wk after treatment. Estimates of the number of lice per animal were made by counting the parasites in three 8-13 cm long hair parts from the following locations: around the ear, below the eyes, muzzle, jaw, brisket, dewlap, shoulders, backline, tailhead, and hips. Numbers of lice were estimated while the animals were restrained in a head gate. Viability of lice was determined by removing specimens from the animals and examining them microscopically. Controls and animals treated with boluses were pastured in a 0.8-ha lot as one herd to maintain pressure for reinfestation from the infested control animals. Cattle in the fifth group were each given a subcutaneous injection (0.2 mg/kg body wt) of moxidectin and were maintained in a separate 0.8-ha lot. Lice were counted on the cattle injected with moxidectin at -15, 0, 2, 13, and 27 d after treatment. Fecal samples (~500 g) were collected from all controls and animals treated with boluses on day 2, and on 1, 2, 4, 6, 8, 10, 12, and 14 wk after treatment. The samples were stored in plastic containers (500 ml) at -200c. They were allowed to thaw to room temperature for 12 h, after which three aliquots (100 g per sample) were placed into
Table 2.
No. (i ± SEM) or S. capillatua (x 10)
00
waxed paper cups (86 ml). Twenty-five newly emerged M. autumnalis larvae were placed into each cup. The cups were then placed inside paper denture containers (237 ml), covered with muslin, and incubated at 38°C (Meyer et al. 1978). After 21 d, the number of adult flies that had emerged were counted. Percentage emergence for each treatment group was corrected by Abbott's (1925) formula. Data were analyzed by repeated measures analysis of variance (ANOVA) and means were compared using Fisher's protected least significant difference test (LSD) (Steel & Torrie 1980). Statistical analyses were done using Statview 512+ statistical software (Feldman et al. 1986). Differences from data analyses were considered significant at P < 0.05.
Results
All animals treated with boluses had significantly reduced populations of S. capillatus at week 1 (Table 1). Numbers of S. capillatus were significantly reduced on the 750 and 1,125 mg (AI) moxidectin treated animals at week 2. All animals treated with boluses had significantly reduced S. capillatus populations from week 4 to week 14. S. capillatus were present on the control animals for the duration of the experiment, although their numbers declined after week 1. Bovicola bovis were first observed on control animals and those treated with boluses at week 2. Populations increased from week 4 (59.2 ± 9.4, f ± SEM) to week 8 (159.2 ± 16.8). No differences in B. bovis populations were observed between control and bolused animals. Counts of B. bouts were
callie injected with 0.2 mg (AI)/kg body wt moxidectin Days after treatment"
Treatment
n
Control Injected
4 5
-15
0
2
13
27
5a 8± 274 ± 181b
8± 5a 308 ± 152b
12 ± 2a o ± Ob
15 ± 5a o ± Ob
10 ± 4a o ± Ob
n, number of animals per treatment group. One animal in the control group died during the test. • Means within each column followed by the same letter were not significantly different (P < 0.05, Fisher's protected LSD test [Steel & Torrie 1980)). Data were transformed to loglO (x + 1) for analyses.
Downloaded from http://jee.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2016
n, number of animals per treatment group. One animal died in the control and 750 mg (AI) group during the test. • Means within each column followed by the same letter were not significantly different (P < 0.05, Fisher's protected LSD test [Steel & Torrie 1980]). Data were transformed to (oglO (x + 1) for analyses.
1268
JOURNAL OF ECONOMIC
Table 3. Corrected percent mortality" (£ ± SEM) of M. autumnai. larvae in feces of callie bolused with 375, 750, or 1,125 mg/kg (AI) moxidectin Time after treatment
Concn, mg/kg n 375 5 5
6 wk
5 5 5
8 10 12 14
wk wk wk wk
5 5
5
5
76.5 68.0 34.5 36.9 75.2 38.8 35.9 20.0 3.2
±
750 18.2
± 9.3 ± 27.2 ± 5.1 ± 0.6 ± 28.4 ± 17.8 ± 4.4 ± 0.7
86.1 84.0 62.6 44.8 74.8 57.6 66.4 35.6 9.5
± 8.0 ± 9.7 ± 27.5 ± 4.6 ± 1.1 ± 13.4 ± 6.9 ± 19.3 ± 2.5
1,125 98.3 94.0 90.8 72.9 88.3 58.2 65.4 30.6 0.0
± ± ± ± ± ± ± ±
1.7 3.7 5.3 3.6 2.7 20.9 17.6 6.7 ± 0.0
n, number of animals per treatment group. n = 4 in the 750 mg (AI) group after week 4. a Mortality corrected using Abbott's formula (1925).
discontinued after week 8, when population reduction was not evident. One hundred percent reduction of S. capillatus on the animals injected with moxidectin was observed on day 2 after treatment (Table 2). These animals were free of S. capillatus for the duration of the experiment. Fecal activity of animals treated with moxidectin boluses was demonstrated by M. autumnalis larval bioassay on day 2 after treatment (Table 3). Percent corrected mortality for M. autumnalis ranged from 98 to 35% through week 10 in all animals treated with boluses. Greater than 90% larval mortality was achieved in manure from the 1,125 mg-treated animals during the first 2 wk of the test. Although 100% M. autumnalis mortality was not seen at any time, larval mortality from control animals and all animals treated with boluses differed significantly at 10 wk. Discussion Moxidectin administered to cattle as a bolus was effective against S. capillatus, even in the presence of reinfestation pressure from control animals. However, moxidectin did not prevent the establishment and growth of B. bovis populations on the same animals. This study was conducted with an experimental bolus and future boluses may perform differently. Alternative control measures against B. bovis would be needed as populations approach economic thresholds on cattle treated with moxidectin. S. capillatus is exposed to blood levels of systemic antiparasitic compounds while ingesting blood from dermal capillaries. B. bovis feeds on epidermal debris (Schmidtmann 1985) and therefore is not affected by these compounds. Strong & Brown (1987) summarized several reports on the effectiveness of ivermectin injections against B. bovis. Meleney (1982) reported no control of B. bovis on cattle injected with ivermectin. Barth (1983) reported 93% mortality of B. bovis after 21 d. Learning (1984) and Schroder et al. (1985) de-
scribed inconsistent control of B. bovis on cattle injected with ivermectin. There are no published reports on the effects of an ivermectin bolus treatment for B. bovis control. Moxidectin excreted in the feces of bolused cattle was effective against M. autumnalis larvae; however, >90% mortality was recorded for only 2 wk in the cattle treated with 1,125 mg/kg (AI) moxidectin. M. autumnalis larval mortality was 90% larval mortality of H. irritans for 4 wk in cattle that received a single injection of 0.2 mg/kg ivermectin. Miller et al. (1981) also reported that larval mortality of M. autumnalis and H. irritans in response to ivermectin was similar, suggesting that the single injection of moxidectin may be effective against M. autumnalis larvae. Cattle lice populations increase during the winter months when M. autumnalis adults are overwintering. The use of moxidectin for sucking lice control during this time will not control M. autumnalis populations in the summer. Moxidectin applications would be required during the summer fly season to be effective against M. autumnalis. We were unable to determine the effect of moxidectin excreted in feces on M. autumnalis adult populations. Acknowledgment This project was partially supported by the American Cyanamid Company, Princeton, New Jersey. This is paper 90-7-152 of the Kentucky Agriculture Experiment Station and ispublished with the approval of the director. References
Cited
Abbott, W. S. 1925. A method of computing the effectiveness of an insecticide. J. Econ. Entomol. 18: 265-267. Barth, D. 1983. Ivomec ein neues antiparasitikum mit endo- und ektoparasitizider wirkung, pp. 95-1ooa. In Symposium Parasitosen der Wiederkauser, Techlenburg. Butler, J. F. 1985. Lice affecting livestock, pp. 101127. In R. E. Williams, R. D. Hall, A. B. Broce & P. J. Scholl [eds.1, Livestock entomology. Wiley, New York. Cummins, L. J. & J. F. Graham. 1982. The effect of lice infestation on the growth of hereford calves. Aust. Vet. J. 58: 194-196.
Downloaded from http://jee.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2016
. 2d 1 wk 2 wk 4 wk
Vol. 84, no. 4
ENTOMOLOGY
August 1991
WEBB ET AL.: MOXIDECTIN
AGAINST CATTLE LICE AND FACE FLIES
B. Broce & P. J. Scholl [eds.], Livestock entomology. Wiley, New York. Schroder, J., G. E. Swan, M. D. SolI & I. K. Hotson. 1985. Efficacy of ivermectin against ectoparasites of cattle in South Africa. J. South Afr. Vet. Assoc. 56: 31-35. SolI, M. D., I. H. Carmichael, G. E. Swan & S. J. Gross. 1989. Control of induced infestations of three african multihost tick species with sustained-release ivermectin. Exp. Appl. Acarol. 7: 121-130. Steel, R.G.D. & J. H. Torrie. 1980. Principles and procedures of statistics a biometrical approach, 2nd ed. McGraw-Hill, New York. Strong, L. & T. A. Brown. 1987. Avermectins in insect control and biology: a review. Bull. Entomol. Res. 77: 357-389. Titehener, R. N. 1985. The control of lice on domestic livestock. Vet. Parasitol. 18: 281-288. Wall, R. & L. Strong. 1987. Environmental consequences of treating cattle with the antiparasitic drug ivermectin. Nature. 327: 418-420. Webb, J. D., S. M. Presley & F. W. Knapp. 1989. Control of face flies and horn flies with experimental diflubenzuron boluses. Insect. Acar. Tests. 14: 375. Wright, J. E. 1975. Insect growth rregulators: development of house flies in feces of bovines fed TH 6040 in mineral blocks and reduction in field populations by surface treatments with TH 6040 or a mixture of stirofos and dichlorvos at larval breeding areas. J. Econ. Entomol. 68: 322-324. Wright, R. E. 1985. Arthropod pests of beef cattle on pasture or rangeland, pp. 191-206. In R. E. Williams, R. D. Hall, A. B. Broce & P. J. Scholl [eds.], Livestock entomology. Wiley, New York. Received for publication 3 October 1990; accepted 12 March 1991.
Downloaded from http://jee.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2016
Drummond, R. O. 1987. Economic aspects of ectoparasites of cattle in North America, pp. 9-24. In W. H. D. Learning & J. Guerrero [eds.], The economic impact of parasitism in cattle. Merck, Sharp & Dohme Agriculture and Veterinary Division, Symposium Proceedings, Veterinary Learning Systems. Feldman, D., J. Gagnon, R. Hofman & J. Simpson. 1986. Statview 512+. Brainpower Inc., Calabasas, Calif. Learning, W.H.D. 1984. Ivermectin as an antiparasitic agent in cattle. Med. Vet. Pract. 65: 669-672. Meleney, W. D. 1982. Control of psoroptic scabies on calves with ivermectin. Am. J. Vet. Res. 43: 329-331. Meyer, J. A., C. M. Christensen & F. W. Knapp. 1978. The influence of various levels of ground ear corn and alfalfa hay in the bovine diet on the development of the face fly. Environ. Entomol. 7: 829-830. Miller, J. A., F. W. Knapp, R. W. Miller & C. W. Pitts. 1979. Sustained-release boluses containing methoprene for control of the horn and face fly. Southwest. Entomol. 4: 195-200. Miller, J. A., S. E. Kunz, D. D. Oehler & R. W. Miller. 1981. Larvicidal activity of Merck MK-933, an avermectin, against the horn fly, stable fly, face fly, and house fly. J. Econ. Entomol. 74: 608-611. Miller, J. A., F. W. Knapp, R. W. Miller, C. W. Pitts & J. Weintraub. 1986. Diflubenzuron bolus for control of fly larvae. J. Agric. Entomol. 3: 48-55. Miller, R. W. 1974. TH 6040 as a feed addditive for control of the face fly and house fly. J. Econ. Entomol. 67: 697. Miller, R. W., F. W. Knapp, R. D. Hall, R. E. Williams, K. E. Doisy & J. D. Webb. 1990. Field evaluation of diflubenzuron boluses for fly control. J. Agric. Entomol. 7: 305-320. Schmidtmann, E. T. 1985. Arthropod pests of dairy cattle, pp. 223-238. In R. E. Williams, R. D. Hall, A.
1269
D. WEBB,
J.
G. BURG, AND F. W. KNAPP
Department of Entomology, University of Kentucky, Lexington, Kentucky 40546
KEY WORDS Insecta, little blue cattle louse, cattle biting louse, systemic insecticide
INFESTATIONS OF lice and face flies, Musca autumnalis De Geer, cause an estimated annual loss of $126 and $52 million, respectively, to the U.S. cattle industry (Drummond 1987). Two common lice species on cattle, Solenoptes capillatus (Enderlein) and Bovicola hovis (L.), have been associated with weight loss, hair damage, and animal irritation. Calves infested with S. capillatus and Linognathus vituli (L.) lost more weight and had lower packed cell volume and hemoglobin measurements during the peak infestation period than un infested calves (Cummins & Graham 1982). One heavily infested heifer lost significant weight even though milk production was not affected (Cummins & Graham 1982). Heavy infestations of B. hovis may result in hair loss from scratching by irritated animals, and lesions may occur at the sites of feeding lice colonies (Butler 1985). M. autumnalis adults do not directly affect weight gain in cattle; however, adult flies have been implicated in the spread of pinkeye and the transmission of eye worms (Thelazia spp.) (Wright 1985). Current methods used for cattle lice control include whole-body dips, powders, sprays, and pourons; for M. autumnalis, treatments include sprays, wipe-on insecticides, dust bags, and feed-through insecticides (Wright 1985). Although these methods provide some control, they are not completely effective and often require multiple applications (Wright 1985, Titchener 1985). S. capillatus was
controlIed for up to 28 d with a single injection of ivermectin (Strong & Brown 1987); however, reinfestation may occur after ivermectin levels have subsided. A slow-release bolus that contains a systemic parasiticide is one method for delivering a prolonged, effective level of treatment to host animals. Slow-release ivermectin formulations are effective in the control of several multi host tick species on cattle (Soli et aI. 1989). Not only does this method provide systemic levels of insecticide in the host blood, but the insecticide may also be excreted in the feces and provide control of manure breeding parasites. Bolus formulations that release 50 ~g/kg of ivermectin per day were lethal to Haematobia irritans (L.) larvae in cattle feces (Wall & Strong 1987). Bolus formulations of diflubenzuron (Miller 1974, Wright 1975, Miller et aI. 1986, Webb et aI. 1989, Miller et aI. 1990) and methoprene (Miller et aI. 1979) have been used to control larval H. irritans and M. autumnalis. Our study was done to determine the effectiveness of moxidectin, a compound with ivermectinlike activity, in controlled-release bolus and injectable formulations for the control of S. capillatus and B. havis on rangeland beef cattle. In addition, the level and persistence of moxidectin activity in cattle feces was determined against M. autumnalis larvae.
, (AmericanCyanamidCL301423), AmericanCyanamidCompany,P.O.Box400,Princeton,N.J.08540.
Twenty-five beef cattle (1l0-320 kg, mixed breed and sex) were randomly assigned to five experi-
Materials and Methods
0022-0493/91/1266-1269$02.00/0 © 1991Entomological Societyof America
Downloaded from http://jee.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2016
J. Econ.Entomol.84(4):1266-1269(1991) ABSTRACT Slow release formulations of 375, 750, and 1,125 mg (AI) in 50-g boluses and a subcutaneous injectable formulation (0.2 mg AI/kg body wt) of moxidectin (CL30l423) were tested for the control of the little blue cattle louse, Solenoptes capillatus (Enderlein), and the cattle biting louse, Bovicola bovis (L). S. capillatus populations were reduced 4 wk after treatment and complete control was observed 6 wk after treatment in groups treated with boluses. B. bovis were first observed at 3 wk and continued to increase throughout the 14-wk te~t period. These were experimental boluses and future boluses may perform differently. Subcutaneous injections of moxidectin gave complete control of S. capillatus for a 27d test period. Feces from animals treated with boluseswere tested with face fly larvae, Musca autumnalis De Geer, to demonstrate fecal activity of moxidectin. Larval mortality in these groups ranged from 90 to 30% from 2 d to 10 wk after treatment.
August 1991
WEBB
ET AL.: MOXIDECTIN
AGAINST
CATTLE
LICE
AND FACE
1267
FLIES
Table 1. No. (£ ± SEM) or S. capillatua (x 10) on callie boluscd with a 50-g bolus per animal containing 375, 750, or 1,150 mg (AI) or moxidectio Wk after treatment"
Treatment
n
Control 375 750 1,125
4 5 4 5
0 160 66 18 96
± ± ± ±
2 17a 19ab 6b 50ab
280 ± 22 ± 5± O±
58a 20b 5b Ob
100 ± 96 ± 2± 18 ±
36a 62a 2b llb
4
6
8
88 ± 12a 14 ± 12b Ob O± 120 ± 120b
62 ± 40a O± Ob O± Ob O± Ob
8 o o o
± ± ± ±
10 Sa Ob Ob Ob
8 o o o
± ± ± ±
Sa Ob Ob Ob
12 15 o o o
± ± ± ±
14 5a Ob Ob ob
10 o o o
± ± ± ±
4a Ob Ob ob
mental groups of five animals each. Before treatment, all animals were weighed and identified with numbered ear tags. One group of animals was used as an untreated control and animals in three groups each received a 50-g bolus containing 375, 750, or 1,125 mg (AI) moxidectin (American Cyanamid Company, Princeton, N.J.). Boluses were administered with a balling gun and the animals were observed for bolus retention. The number of S. capillatus and B. bovis per animal was assessed at day 0 and at 1, 2, 4, 6, 8, 10, 12, and 14 wk after treatment. Estimates of the number of lice per animal were made by counting the parasites in three 8-13 cm long hair parts from the following locations: around the ear, below the eyes, muzzle, jaw, brisket, dewlap, shoulders, backline, tailhead, and hips. Numbers of lice were estimated while the animals were restrained in a head gate. Viability of lice was determined by removing specimens from the animals and examining them microscopically. Controls and animals treated with boluses were pastured in a 0.8-ha lot as one herd to maintain pressure for reinfestation from the infested control animals. Cattle in the fifth group were each given a subcutaneous injection (0.2 mg/kg body wt) of moxidectin and were maintained in a separate 0.8-ha lot. Lice were counted on the cattle injected with moxidectin at -15, 0, 2, 13, and 27 d after treatment. Fecal samples (~500 g) were collected from all controls and animals treated with boluses on day 2, and on 1, 2, 4, 6, 8, 10, 12, and 14 wk after treatment. The samples were stored in plastic containers (500 ml) at -200c. They were allowed to thaw to room temperature for 12 h, after which three aliquots (100 g per sample) were placed into
Table 2.
No. (i ± SEM) or S. capillatua (x 10)
00
waxed paper cups (86 ml). Twenty-five newly emerged M. autumnalis larvae were placed into each cup. The cups were then placed inside paper denture containers (237 ml), covered with muslin, and incubated at 38°C (Meyer et al. 1978). After 21 d, the number of adult flies that had emerged were counted. Percentage emergence for each treatment group was corrected by Abbott's (1925) formula. Data were analyzed by repeated measures analysis of variance (ANOVA) and means were compared using Fisher's protected least significant difference test (LSD) (Steel & Torrie 1980). Statistical analyses were done using Statview 512+ statistical software (Feldman et al. 1986). Differences from data analyses were considered significant at P < 0.05.
Results
All animals treated with boluses had significantly reduced populations of S. capillatus at week 1 (Table 1). Numbers of S. capillatus were significantly reduced on the 750 and 1,125 mg (AI) moxidectin treated animals at week 2. All animals treated with boluses had significantly reduced S. capillatus populations from week 4 to week 14. S. capillatus were present on the control animals for the duration of the experiment, although their numbers declined after week 1. Bovicola bovis were first observed on control animals and those treated with boluses at week 2. Populations increased from week 4 (59.2 ± 9.4, f ± SEM) to week 8 (159.2 ± 16.8). No differences in B. bovis populations were observed between control and bolused animals. Counts of B. bouts were
callie injected with 0.2 mg (AI)/kg body wt moxidectin Days after treatment"
Treatment
n
Control Injected
4 5
-15
0
2
13
27
5a 8± 274 ± 181b
8± 5a 308 ± 152b
12 ± 2a o ± Ob
15 ± 5a o ± Ob
10 ± 4a o ± Ob
n, number of animals per treatment group. One animal in the control group died during the test. • Means within each column followed by the same letter were not significantly different (P < 0.05, Fisher's protected LSD test [Steel & Torrie 1980)). Data were transformed to loglO (x + 1) for analyses.
Downloaded from http://jee.oxfordjournals.org/ at University of Iowa Libraries/Serials Acquisitions on June 7, 2016
n, number of animals per treatment group. One animal died in the control and 750 mg (AI) group during the test. • Means within each column followed by the same letter were not significantly different (P < 0.05, Fisher's protected LSD test [Steel & Torrie 1980]). Data were transformed to (oglO (x + 1) for analyses.
1268
JOURNAL OF ECONOMIC
Table 3. Corrected percent mortality" (£ ± SEM) of M. autumnai. larvae in feces of callie bolused with 375, 750, or 1,125 mg/kg (AI) moxidectin Time after treatment
Concn, mg/kg n 375 5 5
6 wk
5 5 5
8 10 12 14
wk wk wk wk
5 5
5
5
76.5 68.0 34.5 36.9 75.2 38.8 35.9 20.0 3.2
±
750 18.2
± 9.3 ± 27.2 ± 5.1 ± 0.6 ± 28.4 ± 17.8 ± 4.4 ± 0.7
86.1 84.0 62.6 44.8 74.8 57.6 66.4 35.6 9.5
± 8.0 ± 9.7 ± 27.5 ± 4.6 ± 1.1 ± 13.4 ± 6.9 ± 19.3 ± 2.5
1,125 98.3 94.0 90.8 72.9 88.3 58.2 65.4 30.6 0.0
± ± ± ± ± ± ± ±
1.7 3.7 5.3 3.6 2.7 20.9 17.6 6.7 ± 0.0
n, number of animals per treatment group. n = 4 in the 750 mg (AI) group after week 4. a Mortality corrected using Abbott's formula (1925).
discontinued after week 8, when population reduction was not evident. One hundred percent reduction of S. capillatus on the animals injected with moxidectin was observed on day 2 after treatment (Table 2). These animals were free of S. capillatus for the duration of the experiment. Fecal activity of animals treated with moxidectin boluses was demonstrated by M. autumnalis larval bioassay on day 2 after treatment (Table 3). Percent corrected mortality for M. autumnalis ranged from 98 to 35% through week 10 in all animals treated with boluses. Greater than 90% larval mortality was achieved in manure from the 1,125 mg-treated animals during the first 2 wk of the test. Although 100% M. autumnalis mortality was not seen at any time, larval mortality from control animals and all animals treated with boluses differed significantly at 10 wk. Discussion Moxidectin administered to cattle as a bolus was effective against S. capillatus, even in the presence of reinfestation pressure from control animals. However, moxidectin did not prevent the establishment and growth of B. bovis populations on the same animals. This study was conducted with an experimental bolus and future boluses may perform differently. Alternative control measures against B. bovis would be needed as populations approach economic thresholds on cattle treated with moxidectin. S. capillatus is exposed to blood levels of systemic antiparasitic compounds while ingesting blood from dermal capillaries. B. bovis feeds on epidermal debris (Schmidtmann 1985) and therefore is not affected by these compounds. Strong & Brown (1987) summarized several reports on the effectiveness of ivermectin injections against B. bovis. Meleney (1982) reported no control of B. bovis on cattle injected with ivermectin. Barth (1983) reported 93% mortality of B. bovis after 21 d. Learning (1984) and Schroder et al. (1985) de-
scribed inconsistent control of B. bovis on cattle injected with ivermectin. There are no published reports on the effects of an ivermectin bolus treatment for B. bovis control. Moxidectin excreted in the feces of bolused cattle was effective against M. autumnalis larvae; however, >90% mortality was recorded for only 2 wk in the cattle treated with 1,125 mg/kg (AI) moxidectin. M. autumnalis larval mortality was 90% larval mortality of H. irritans for 4 wk in cattle that received a single injection of 0.2 mg/kg ivermectin. Miller et al. (1981) also reported that larval mortality of M. autumnalis and H. irritans in response to ivermectin was similar, suggesting that the single injection of moxidectin may be effective against M. autumnalis larvae. Cattle lice populations increase during the winter months when M. autumnalis adults are overwintering. The use of moxidectin for sucking lice control during this time will not control M. autumnalis populations in the summer. Moxidectin applications would be required during the summer fly season to be effective against M. autumnalis. We were unable to determine the effect of moxidectin excreted in feces on M. autumnalis adult populations. Acknowledgment This project was partially supported by the American Cyanamid Company, Princeton, New Jersey. This is paper 90-7-152 of the Kentucky Agriculture Experiment Station and ispublished with the approval of the director. References
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. 2d 1 wk 2 wk 4 wk
Vol. 84, no. 4
ENTOMOLOGY
August 1991
WEBB ET AL.: MOXIDECTIN
AGAINST CATTLE LICE AND FACE FLIES
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