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Comparative Efficacy of Plastic Strips Impregnated with Permethrin and Permethrin Dust for Northern Fowl Mite Control on Caged Laying Hens1,2
Comparative Efficacy of Plastic Strips Impregnated with Permethrin and Permethrin Dust for Northern Fowl Mite Control on Caged Laying Hens1'2 R. D. HALL, J. M. VANDEPOPULIERE,3 F. J. FISCHER, J. J. LYONS, 3 and K. E. DOISY Department ofEntomology;
University of Missouri, Columbia, Missouri 65211
(Received for publication July 19, 1982) ABSTRACT Established populations of northern fowl mites, Ornithonyssus sylviarum (Canestrini and Fanzago), on caged laying hens were effectively controlled within 77 days by application of two plastic strips impregnated with permethrin per cage. Such strips contained 9.6% active ingredient (wt/wt), were ca. 20.5-cm long, and were affixed to the top cage wires. Use of only one strip per cage resulted in less control, approximating that obtained with .25% permethrin dust. Egg mass, expressed as gram egg per hen per day, was significantly greater in all treated groups. (Key words: acaricide, northern fowl mite, permethrin dust, permethrin strips, caged hens) 1983 Poultry Science 62:612-615 INTRODUCTION
The northern fowl mite, Ornithonyssus sylviarum (Canestrini and Fanzago), is a widespread blood-feeding ectoparasite of poultry and many wild birds. Poultrymen currently consider this species the external parasite of greatest importance to caged laying hens in the US (DeVaney, 1978). Large populations may cause anemia and death in roosters; however, reported effects on egg production by hens are variable (Loomis et al, 1970; Matthysse et al., 1974; DeVaney, 1979; Eklund et al, 1980). Justification of control programs typically involves consideration of fractional production losses in the context of large caged layer flocks. Of equal or greater importance is the reluctance of workers to perform their duties inside infested facilities. Northern fowl mite populations existing on caged layers are currently controlled satisfactorily only via application of acaricidal materials. Organophosphorous or carbamate materials comprise the majority of such compounds in widespread use. In recent years, considerable interest has been shown in the potential of synthetic pyrethroid acaricides for northern fowl mite control. Demonstrating high acute toxicity to these mites, acceptable residual activity, low requisite concentrations,
1
Acari: Macronyssidae. Contribution of the Missouri Agricultural Experiment Station Journal Series No. 9159. This work was supported by the Missouri Egg Merchandising Council and by Philips Roxane, Inc. 3 Department of Poultry Science. 2
and a low order of acute toxicity to poultry, fenvalerate and permethrin appear to be wellsuited for this use (Hall et al, 1978; Loomis et al, 1979; Lancaster and Simco, 1980; Loomis and Dunning, 1980; Williams and Berry, 1980; Collison et al, 1981; Arthur and Axtell, 1982). Application techniques evaluated included high or low pressure sprays and dust treatments. The trend toward minimum insecticide or acaricide application to livestock has been facilitated by recent innovations employing treated plastic. This material frequently permits long-term, slow release of such compounds and has found wide acceptance in the form of treated ear tags for cattle (Harvey and Brethour, 1970; Ahrens, 1977; Ahrens and Cocke, 1979). The two synthetic pyrethroid chemicals mentioned earlier have proven well-suited for this type of application. When permethrinimpregnated plastic strips became available for testing, they were evaluated for efficacy against northern fowl mites. MATERIALS AND METHODS
Birds Used and Caging System. A total of 240 Heisdorf and Nelson strain Single Comb White Leghorn hens was used for this experiment. Debeaked as chicks, these birds were 10 months old at the start of the test and were housed 2 per cage in double tier .06 m 3 wire units suspended over a concrete floor. They were chosen at random from a larger flock with the sole selection criterion being the presence of an active northern fowl mite infestation. Treatments were assigned at random to blocks of 60 hens in two replicates
612
EFFICACY OF PERMETHRIN STRIPS
613
TABLE 1. Northern fowl mite infestation indices for groups of hens untreated and treated with one or two permethrin-impregnated plastic strips per cage or .25% active ingredient (AI) permetbrin dust Average mite index on day posttreatment 1 Acaricide treatment
Pretreatment
3
7
13
21
28
35
Untreated control Permethrin strips (2/cage) Permethrin strip (1/cage) Permethrin dust (.25% AI)
2.87a 3.08 a 3.13a 3.13 a
2.75 b 3.23 a b 3.38 a .70 c
2.70 a 2.22 a 2.76 a .35b
2.45 a 1.70 b 2.31 a .18 c
2.87 a 1.32 b 2.48 a .07 c
2.42 a .78 c 1.47b .07 d
2.53 a .52 c 1.02 b .05 d
42
49
56
63
70
77
Untreated control Permethrin strips (2/cage) Permethrin strip (1/cage) Permethrin dust (.25% AI)
a
2.10 .12C .89° .13 c
a
1.71 .02 b .48 b .22 b
a
1.78 .05b .26 b .35b
a
1.66 .03b .21b .40 b
a
1.32 .05b .30 b .27 b
1.44a Ob
.21b .40 b
' ' ' Averages within columns not followed by a common letter are significantly different (P<.05) by the least significant range test. 'Mite rating scheme: 0 = 0 mites, 1 = 1-5 mites, 2 = 6-15 mites, 3 = 16-50 mites, 4 = 51-100 mites, 5 = 101-500 mites, 6 = more than 500 mites.
balanced evenly between upper and lower tiers. Feed (a standard layer mash) and water were supplied ad lib and lighting was automatically controlled on a 14 hr light: 10 hr dark cycle. Eggs were collected each day and weighed each week. Feed consumption was measured by weighing the uneaten portion of the weekly allocation. Mite Rating System. Northern fowl mite infestation levels were rated prior to treatment and at regular intervals thereafter by using the following index system: 0 = no live mites seen, 1 = 1-5 mites, 2 = 6-15 mites, 3 = 16-50 mites, 4 = 51-100 mites, 5 = 101-500 mites, and 6 = more than 500 mites. Examination was done by removing each hen from its cage, holding it so that the vent region could be inspected easily, and confining mite counts to this area. Approximately 30 sec were required to adequately assess each chicken. Inspectors' responsibilities were divided across treatment replicates to minimize the effect of possible counting bias on subsequent analyses. Treatment Protocol. Plastic strips measuring 2.54 x 20.6 cm were assayed by the manufacturer 4 to contain .79 g permethrin each. Such strips were prepared by punching a small
hole near one end and hanging them from the top cage wires with noncorrosive hog rings. All strips were positioned ca. 15 cm from the front cage margin. The rates evaluated were one or two strips per cage. Cages treated with one strip had the device hung in the middle, and cages treated with two strips had them affixed side-by-side and each about one-third of the cage width in from the lateral walls. When the caged hens moved about, the strips contacted the upper and side body areas. Permethrin .25% active ingredient (AI) dust 5 was applied to designated hens at the rate of 454 g (1 lb)/100 birds. A small shaker can was used to sprinkle weighed amounts of the material directly on the backs of hens in each appropriate replicate. No attempt was made to treat the vent area, and interbird contact was depended upon to effect transfer of the acaricide to this region (Hall et al., 1981). Statistical Analyses. Data resulting from each inspection period were subjected to the analysis of variance (ANOVA) and least significant range (LSR) procedures. Because of the semi-logarithmic nature of the rating system, no further transformations were required. Production data were evaluated using Duncan's new multiple range test.
"Philips Roxane, Inc., 2621 North Belt Highway, St. Joseph, MO 64502. 5 ICI Americas, Inc., Agricultural Chemicals Division, P.O. Box 208, Goldsboro, NC 27530.
RESULTS AND DISCUSSION
Pretreatment mite ratings indicated that all groups of experimental hens had similar nor-
614
HALL ET AL.
TABLE 2. Production performance of northern fowl mite-infested hens untreated and treated with permethrin impregnated plastic strips or permethrin dust
Acaricide treatment
Untreated control Permethrin strips (2/cage) Permethrin strip (1/cage) Permethrin dust (.25% AI) 2
Production
Feed consumption
(Hen-day, %)
(Hen-day, g)
73.12b 1 7944ab 82.16 a 78.75 a b
113.5 a 119.2 a 117.5 a 117.9 a
Egg weight (g) 59.57 a 58.83 a 58.75 a 59.61 a
Egg mass (g egg/ hen-day) 43.2b 46.7 a 48.3 a 46.8 a
Feed efficiency (gegg/ g feed) .38 a .39 a .41a .40 a
1 Averages within columns not followed by a common letter are significantly different (P<.05) by the Duncan's new multiple range test. 2
AI, active ingredient.
thern fowl mite infestations prior to treatment (Table 1). No differences between mite populations on untreated control birds and hens treated with permethrin-impregnated plastic strips were apparent for ca. 2 weeks. Subsequent to this time, average mite ratings on the hens in the two strips per cage treatments began to decline steadily and reached a very low level (average index = .02) 49 days posttreatment. Mites were eliminated from these hens 77 days after the strips were applied. In contrast, mite populations did not decrease as rapidly in the one strip per cage treatments. Average indices on the latter hens were not significantly different from those on the control group for ca. 4 weeks posttreatment. After this time, however, mite populations decreased in the one strip per cage treatments and were small (average index = .21) when the test was ended 11 weeks postteatment. The .25% AI permethrin dust was noted to reduce mite populations more rapidly then did the impregnated plastic strips. Three days after application, birds in the dust treatment supported significantly fewer northern fowl mites than did hens in any other group. Mite populations on the dusttreated chickens continued to decline for a total of 35 days, when an average index of .05 was reached. These results confirm the effectiveness of interbird distribution of acaricidal dust treatments and the utility of permethrin dust formulation applied only to the backs of caged poultry. Approximately 4 weeks after treatment, mite populations on the dusted hens began to increase. When the experiment was terminated, the dust-treated group supported the second largest
average mite infestation (.40). Efficacy profile for .25% AI permethrin dust was similar to one with application made directly to the vent area (Arthur and Axtell, 1982). Production data indicate that hens in all treatment groups had a greater egg mass output expressed as grams egg per hen per day than did untreated control hens (Table 2). Chickens in the one permethrin strip per cage treatment laid significantly more eggs than did the control birds. No significant differences between treatment groups were detected with feed consumption, egg weight, or feed efficiency (gram egg /gram feed); however, the untreated hens exhibited the numerically poorest feed efficiency performance. The results of this experiment indicate that a slow release, plastic formulation of permethrin, applied as strips hung in cages, is capable of controlling established populations of northern fowl mites on hens. For the time evaluated, such strips were ultimately more effective than .25% AI permethrin dust treatments. A random sample of 10 strips produced an average weight of 8.3 g each; consequently, the acaricide was present in the formulation at a final concentration of 9.6%. This approximates the concentration of permethrin currently employed in plastic ear tags for cattle, and the actual surface areas of both types of device are similar. No detectable permethrin residues were present in yolk samples from eggs laid through 35 days postapplication by hens in the two strip per cage or dust treatments (W. C. McGuire, personal communication). It is probable that the efficiency of the plastic strip system could be increased by
EFFICACY OF PERMETHRIN STRIPS lowering t h e height of t h e strips inside t h e cages via short lengths of chain. This would have t h e effect of increasing c o n t a c t b e t w e e n t h e hens and t h e t o t a l length of t h e strips e m p l o y e d . An effective, long-term form of n o r t h e r n fowl m i t e c o n t r o l w o u l d be a valuable asset t o p o u l t r y p r o d u c e r s . T h e p o t e n t i a l for plastic formulations of s y n t h e t i c p y r e t h r o i d acaricides is therefore well w o r t h additional investigation, especially in t h e c o n t e x t of fully a u t o m a t e d facilities w h e r e access t o hens is often severely limited. I m p o r t a n t questions t h a t remain u n a n s w e r e d include t h e 1) value of such form u l a t i o n s as p r o p h y l a x i s against n o r t h e r n fowl mites o n uninfested flocks and 2) longevity of these materials in c o n j u n c t i o n w i t h e c o n o m i c benefit. ACKNOWLEDGMENTS W. C. McGuire, Philips R o x a n e , Inc., supplied t h e plastic strips used in this e x p e r i m e n t and m a d e residue analyses available t o us. G. B. Braithwaite, ICI Americas, Inc., provided t h e p e r m e t h r i n dust, and J. R. Poe supervised m a i n t e n a n c e of t h e t e s t p o u l t r y .
REFERENCES Ahrens, E. H., 1977. Horn fly control with an insecticide impregnated ear tag. Southwest. Entomol. 2 : 8 - 1 0 . Ahrens, E. H., and J. Cocke, 1979. Season long horn fly control with an insecticide impregnated ear tag. J. Econ. Entomol. 72:210. Arthur, F. H., and R. C. Axtell, 1982. Comparisons of permethrin formulations and application methods for northern fowl mite control on caged laying hens. Poultry Sci. 61:879-884. Collison, C. H., R. G. Danka, and D. R. Kennell, 1981. An evaluation of permethrin, carbaryl, and amitraz for the control of northern fowl mites on caged chickens. Poultry Sci. 60:1812—1817.
615
DeVaney, J. A., 1978. A survey of poultry ectoparasite problems and their research in the United States. Poultry Sci. 57:1217-1220. DeVaney, J. A., 1979. Effects of the northern fowl mite, Ornitbonyssus sylviarum, on egg production and body weight of caged White Leghorn hens. Poultry Sci. 58:191-194. Eklund, J., E. Loomis, and H. Abplanalp, 1980. Genetic resistance of White Leghorn chickens to infestation by the northern fowl mite, Ornitbonyssus sylviarum. Arch. Gefliigelkd 44: 195-199. Hall, R. D., M. C. Foehse, and J. M. Vandepopuliere, 1981. Application phenomena and efficacy of concentrated acaricide dusts for northern fowl mite control on caged laying hens. Poultry Sci. 60:1187-1194. Hall, R. D„ L. H. Townsend, Jr., and E. C. Turner, Jr., 1978. Laboratory and field tests to compare the effectiveness of organophosphorous, carbamate, and synthetic pyrethroid acaricides against northern fowl mites. J. Econ. Entomol. 71: 315-318. Harvey, T. L., and J. R. Brethour, 1970. Horn fly control with dichlorvos-impregnated strips. J. Econ. Entomol. 63: 1688-1689. Lancaster, J. L., and J. S. Simco, 1980. Effects of a pyrethroid against northern fowl mite. Arkansas Farm Res. (Jan.-Feb.):9. Loomis, E. C , E. L. Bramhall, J. A. Allen, R. A. Ernst, and L. L. Dunning, 1970. Effects of the northern fowl mite on White Leghorn chickens. J. Econ. Entomol. 63:1885-1889. Loomis, E. C , E. L. Bramhall, and L. L. Dunning, 1979. Comparative effectiveness of fenvalerate and carbaryl sprays against the northern fowl mite. J. Econ. Entomol. 72:856-859. Loomis, E. C , and L. L. Dunning, 1980. Synthetic pyrethroids effective against northern fowl mite. California Agric. 34:10—11. Matthysse, J. G., C. J. Jones, and A. Purnasiri, 1974. Development of northern fowl mite populations on chickens, effects on the host, and immunology. Search Agric. 4(9): 1-39. Williams, R. E., and J. G. Berry, 1980. Control of northern fowl mite with permethrin and fenvalerate, two synthetic pyrethroid compounds. Poultry Sci. 59:1211-1214.
University of Missouri, Columbia, Missouri 65211
(Received for publication July 19, 1982) ABSTRACT Established populations of northern fowl mites, Ornithonyssus sylviarum (Canestrini and Fanzago), on caged laying hens were effectively controlled within 77 days by application of two plastic strips impregnated with permethrin per cage. Such strips contained 9.6% active ingredient (wt/wt), were ca. 20.5-cm long, and were affixed to the top cage wires. Use of only one strip per cage resulted in less control, approximating that obtained with .25% permethrin dust. Egg mass, expressed as gram egg per hen per day, was significantly greater in all treated groups. (Key words: acaricide, northern fowl mite, permethrin dust, permethrin strips, caged hens) 1983 Poultry Science 62:612-615 INTRODUCTION
The northern fowl mite, Ornithonyssus sylviarum (Canestrini and Fanzago), is a widespread blood-feeding ectoparasite of poultry and many wild birds. Poultrymen currently consider this species the external parasite of greatest importance to caged laying hens in the US (DeVaney, 1978). Large populations may cause anemia and death in roosters; however, reported effects on egg production by hens are variable (Loomis et al, 1970; Matthysse et al., 1974; DeVaney, 1979; Eklund et al, 1980). Justification of control programs typically involves consideration of fractional production losses in the context of large caged layer flocks. Of equal or greater importance is the reluctance of workers to perform their duties inside infested facilities. Northern fowl mite populations existing on caged layers are currently controlled satisfactorily only via application of acaricidal materials. Organophosphorous or carbamate materials comprise the majority of such compounds in widespread use. In recent years, considerable interest has been shown in the potential of synthetic pyrethroid acaricides for northern fowl mite control. Demonstrating high acute toxicity to these mites, acceptable residual activity, low requisite concentrations,
1
Acari: Macronyssidae. Contribution of the Missouri Agricultural Experiment Station Journal Series No. 9159. This work was supported by the Missouri Egg Merchandising Council and by Philips Roxane, Inc. 3 Department of Poultry Science. 2
and a low order of acute toxicity to poultry, fenvalerate and permethrin appear to be wellsuited for this use (Hall et al, 1978; Loomis et al, 1979; Lancaster and Simco, 1980; Loomis and Dunning, 1980; Williams and Berry, 1980; Collison et al, 1981; Arthur and Axtell, 1982). Application techniques evaluated included high or low pressure sprays and dust treatments. The trend toward minimum insecticide or acaricide application to livestock has been facilitated by recent innovations employing treated plastic. This material frequently permits long-term, slow release of such compounds and has found wide acceptance in the form of treated ear tags for cattle (Harvey and Brethour, 1970; Ahrens, 1977; Ahrens and Cocke, 1979). The two synthetic pyrethroid chemicals mentioned earlier have proven well-suited for this type of application. When permethrinimpregnated plastic strips became available for testing, they were evaluated for efficacy against northern fowl mites. MATERIALS AND METHODS
Birds Used and Caging System. A total of 240 Heisdorf and Nelson strain Single Comb White Leghorn hens was used for this experiment. Debeaked as chicks, these birds were 10 months old at the start of the test and were housed 2 per cage in double tier .06 m 3 wire units suspended over a concrete floor. They were chosen at random from a larger flock with the sole selection criterion being the presence of an active northern fowl mite infestation. Treatments were assigned at random to blocks of 60 hens in two replicates
612
EFFICACY OF PERMETHRIN STRIPS
613
TABLE 1. Northern fowl mite infestation indices for groups of hens untreated and treated with one or two permethrin-impregnated plastic strips per cage or .25% active ingredient (AI) permetbrin dust Average mite index on day posttreatment 1 Acaricide treatment
Pretreatment
3
7
13
21
28
35
Untreated control Permethrin strips (2/cage) Permethrin strip (1/cage) Permethrin dust (.25% AI)
2.87a 3.08 a 3.13a 3.13 a
2.75 b 3.23 a b 3.38 a .70 c
2.70 a 2.22 a 2.76 a .35b
2.45 a 1.70 b 2.31 a .18 c
2.87 a 1.32 b 2.48 a .07 c
2.42 a .78 c 1.47b .07 d
2.53 a .52 c 1.02 b .05 d
42
49
56
63
70
77
Untreated control Permethrin strips (2/cage) Permethrin strip (1/cage) Permethrin dust (.25% AI)
a
2.10 .12C .89° .13 c
a
1.71 .02 b .48 b .22 b
a
1.78 .05b .26 b .35b
a
1.66 .03b .21b .40 b
a
1.32 .05b .30 b .27 b
1.44a Ob
.21b .40 b
' ' ' Averages within columns not followed by a common letter are significantly different (P<.05) by the least significant range test. 'Mite rating scheme: 0 = 0 mites, 1 = 1-5 mites, 2 = 6-15 mites, 3 = 16-50 mites, 4 = 51-100 mites, 5 = 101-500 mites, 6 = more than 500 mites.
balanced evenly between upper and lower tiers. Feed (a standard layer mash) and water were supplied ad lib and lighting was automatically controlled on a 14 hr light: 10 hr dark cycle. Eggs were collected each day and weighed each week. Feed consumption was measured by weighing the uneaten portion of the weekly allocation. Mite Rating System. Northern fowl mite infestation levels were rated prior to treatment and at regular intervals thereafter by using the following index system: 0 = no live mites seen, 1 = 1-5 mites, 2 = 6-15 mites, 3 = 16-50 mites, 4 = 51-100 mites, 5 = 101-500 mites, and 6 = more than 500 mites. Examination was done by removing each hen from its cage, holding it so that the vent region could be inspected easily, and confining mite counts to this area. Approximately 30 sec were required to adequately assess each chicken. Inspectors' responsibilities were divided across treatment replicates to minimize the effect of possible counting bias on subsequent analyses. Treatment Protocol. Plastic strips measuring 2.54 x 20.6 cm were assayed by the manufacturer 4 to contain .79 g permethrin each. Such strips were prepared by punching a small
hole near one end and hanging them from the top cage wires with noncorrosive hog rings. All strips were positioned ca. 15 cm from the front cage margin. The rates evaluated were one or two strips per cage. Cages treated with one strip had the device hung in the middle, and cages treated with two strips had them affixed side-by-side and each about one-third of the cage width in from the lateral walls. When the caged hens moved about, the strips contacted the upper and side body areas. Permethrin .25% active ingredient (AI) dust 5 was applied to designated hens at the rate of 454 g (1 lb)/100 birds. A small shaker can was used to sprinkle weighed amounts of the material directly on the backs of hens in each appropriate replicate. No attempt was made to treat the vent area, and interbird contact was depended upon to effect transfer of the acaricide to this region (Hall et al., 1981). Statistical Analyses. Data resulting from each inspection period were subjected to the analysis of variance (ANOVA) and least significant range (LSR) procedures. Because of the semi-logarithmic nature of the rating system, no further transformations were required. Production data were evaluated using Duncan's new multiple range test.
"Philips Roxane, Inc., 2621 North Belt Highway, St. Joseph, MO 64502. 5 ICI Americas, Inc., Agricultural Chemicals Division, P.O. Box 208, Goldsboro, NC 27530.
RESULTS AND DISCUSSION
Pretreatment mite ratings indicated that all groups of experimental hens had similar nor-
614
HALL ET AL.
TABLE 2. Production performance of northern fowl mite-infested hens untreated and treated with permethrin impregnated plastic strips or permethrin dust
Acaricide treatment
Untreated control Permethrin strips (2/cage) Permethrin strip (1/cage) Permethrin dust (.25% AI) 2
Production
Feed consumption
(Hen-day, %)
(Hen-day, g)
73.12b 1 7944ab 82.16 a 78.75 a b
113.5 a 119.2 a 117.5 a 117.9 a
Egg weight (g) 59.57 a 58.83 a 58.75 a 59.61 a
Egg mass (g egg/ hen-day) 43.2b 46.7 a 48.3 a 46.8 a
Feed efficiency (gegg/ g feed) .38 a .39 a .41a .40 a
1 Averages within columns not followed by a common letter are significantly different (P<.05) by the Duncan's new multiple range test. 2
AI, active ingredient.
thern fowl mite infestations prior to treatment (Table 1). No differences between mite populations on untreated control birds and hens treated with permethrin-impregnated plastic strips were apparent for ca. 2 weeks. Subsequent to this time, average mite ratings on the hens in the two strips per cage treatments began to decline steadily and reached a very low level (average index = .02) 49 days posttreatment. Mites were eliminated from these hens 77 days after the strips were applied. In contrast, mite populations did not decrease as rapidly in the one strip per cage treatments. Average indices on the latter hens were not significantly different from those on the control group for ca. 4 weeks posttreatment. After this time, however, mite populations decreased in the one strip per cage treatments and were small (average index = .21) when the test was ended 11 weeks postteatment. The .25% AI permethrin dust was noted to reduce mite populations more rapidly then did the impregnated plastic strips. Three days after application, birds in the dust treatment supported significantly fewer northern fowl mites than did hens in any other group. Mite populations on the dusttreated chickens continued to decline for a total of 35 days, when an average index of .05 was reached. These results confirm the effectiveness of interbird distribution of acaricidal dust treatments and the utility of permethrin dust formulation applied only to the backs of caged poultry. Approximately 4 weeks after treatment, mite populations on the dusted hens began to increase. When the experiment was terminated, the dust-treated group supported the second largest
average mite infestation (.40). Efficacy profile for .25% AI permethrin dust was similar to one with application made directly to the vent area (Arthur and Axtell, 1982). Production data indicate that hens in all treatment groups had a greater egg mass output expressed as grams egg per hen per day than did untreated control hens (Table 2). Chickens in the one permethrin strip per cage treatment laid significantly more eggs than did the control birds. No significant differences between treatment groups were detected with feed consumption, egg weight, or feed efficiency (gram egg /gram feed); however, the untreated hens exhibited the numerically poorest feed efficiency performance. The results of this experiment indicate that a slow release, plastic formulation of permethrin, applied as strips hung in cages, is capable of controlling established populations of northern fowl mites on hens. For the time evaluated, such strips were ultimately more effective than .25% AI permethrin dust treatments. A random sample of 10 strips produced an average weight of 8.3 g each; consequently, the acaricide was present in the formulation at a final concentration of 9.6%. This approximates the concentration of permethrin currently employed in plastic ear tags for cattle, and the actual surface areas of both types of device are similar. No detectable permethrin residues were present in yolk samples from eggs laid through 35 days postapplication by hens in the two strip per cage or dust treatments (W. C. McGuire, personal communication). It is probable that the efficiency of the plastic strip system could be increased by
EFFICACY OF PERMETHRIN STRIPS lowering t h e height of t h e strips inside t h e cages via short lengths of chain. This would have t h e effect of increasing c o n t a c t b e t w e e n t h e hens and t h e t o t a l length of t h e strips e m p l o y e d . An effective, long-term form of n o r t h e r n fowl m i t e c o n t r o l w o u l d be a valuable asset t o p o u l t r y p r o d u c e r s . T h e p o t e n t i a l for plastic formulations of s y n t h e t i c p y r e t h r o i d acaricides is therefore well w o r t h additional investigation, especially in t h e c o n t e x t of fully a u t o m a t e d facilities w h e r e access t o hens is often severely limited. I m p o r t a n t questions t h a t remain u n a n s w e r e d include t h e 1) value of such form u l a t i o n s as p r o p h y l a x i s against n o r t h e r n fowl mites o n uninfested flocks and 2) longevity of these materials in c o n j u n c t i o n w i t h e c o n o m i c benefit. ACKNOWLEDGMENTS W. C. McGuire, Philips R o x a n e , Inc., supplied t h e plastic strips used in this e x p e r i m e n t and m a d e residue analyses available t o us. G. B. Braithwaite, ICI Americas, Inc., provided t h e p e r m e t h r i n dust, and J. R. Poe supervised m a i n t e n a n c e of t h e t e s t p o u l t r y .
REFERENCES Ahrens, E. H., 1977. Horn fly control with an insecticide impregnated ear tag. Southwest. Entomol. 2 : 8 - 1 0 . Ahrens, E. H., and J. Cocke, 1979. Season long horn fly control with an insecticide impregnated ear tag. J. Econ. Entomol. 72:210. Arthur, F. H., and R. C. Axtell, 1982. Comparisons of permethrin formulations and application methods for northern fowl mite control on caged laying hens. Poultry Sci. 61:879-884. Collison, C. H., R. G. Danka, and D. R. Kennell, 1981. An evaluation of permethrin, carbaryl, and amitraz for the control of northern fowl mites on caged chickens. Poultry Sci. 60:1812—1817.
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