Power Dusting with Organophosphorus Insecticides to Control the Sheep Ked!,2 R. E. PFADT,J. E. LLOYD,and E. W. SPACKMAN Entomology Section, University of Wyoming, Laramie 82071 ABSTRACT and 5%, and phosmet I %. Ronnel I '70 applied below recommended rates did not eradicate infestations. Shear· ing sheep before lambing reduced populations of sheep keds an average 77% compared with the populations on flocks sheared after lambing.
Tests of power dusting sheep for control of the sheep ked, Melophagus ovinus (L.), have been continued with organophosphorus insecticides of desirable veterinary characteristics, i.e., low toxicity to mammals and limited residual. Determination of effectiveness of control, the 3rd important characteristic, was the objective of this study. Pfadt and Lavigne (1965) investigated the effectiveness of 5 organophosphorus dusts and I carbamate dust. They found that ked infestations could be eradicated from individual flocks by power dusting with 2% diazinon and I % ronnel, and high reductions of populations achieved by dusting with 0.5% coumaphos, 2% dioxathion, and 4% malathion. Because anything less than eradication permits populations to 'build up during the following fall and winter, our goal was to find insecticides, concentrations, and rates of application of dusts whidl provide this degree of control. In the present tests, we used for the first time dusts of crotoxyphos, phosmet, and stirofos and have repeated testing of coumaphos and ronnel either at different concentrations or at different rates of application. METHODS.-All sheep in a flock were treated with a single insecticide of a given concentration and rate of application to evaluate the performance of the dust. Each dust was tested on at least 2 flocks. AlI sheep in a flock were driven throug'h a curtain of dust generated and expelled by a power duster through outlets in a steel sheep chute (Howry-Berg Sheep Duster). Dusting rates were controlled by a sliding shutter on a circular opening in the bottom of the hopper. The actual dusting rate was calculated by weighing the dust before and after treatment and timing the duration of the dusting period. Sheep ked density was determined by a total count of adults on 5 lambs and 5 ewes of each flock immediately before treatment and again 6 wk later. The interval between examinations provided sufficient time for all pupae present at the time of dusting to emerge as adults. Untreated flocks were examined in the same manner and at the same time interval as treated flocks for comparison. Percen tage reduction of sheep keds,
however, was computed from the pre- and posttreatment counts of each treated flock without use of check mortality. Testing was done on farm flocks in southeast Wyoming. Out of 30 flocks, 24 were white face or white crossed breeds and 6 were black face breeds or white crossed with black. Number of sheep and lambs in flocks ranged from 27-964 and averaged 223. The median sized flock was 108. Flocks were dusted be· tween 15 and 84 days (average 48 days) after shearing in those flocks sheared after lambing and from 69 to III days (avg 86 days) after shearing in those flocks sheared before lambing. RESULTS AND DISCUSSION.-Table I summarizes results of power dusting shorn sheep in spring with 5 organophosphorus insecticides. Although most of the dusts caused significant reduction of sheep ked populations, only a few achieved our goal of eradication. At rates of 2.5 and 3.1 Ib/min, 1% coumaphos provided eradication, but at lower rates, 1.8, 2.1, 2.3 lb/ min, this dust did not provide eradication. Neither did 0.5% coumaphos, which was evaluated at rates of 2.0 and 2.7 lb/min only. Similar results were obtained in previous trials with rates of 3 and 3.5 Ib/ min of 0.5'70 coumaphos (Pfadt and Lavigne 1965). Stirofos of 3% and 5% sometimes provided eradication when populations of sheep keds were low, i.e., I.I and 4.9/head, but generally these dusts were ineffective in eliminating populations completely. Crotoxyphos 3% and phosmet I % did not provide eradication even at high rates of application, 4.1 and 3.5 Ib/min, respectively. At rates of 1.4 and 2 lb/min, 1% ronnel did not achieve eradication, 'but Pfadt and Lavigne (1965) obtained eradication with this dust at rates of 2.6 and 3.3Ib/min. Of 7 organophosphorus insecticides tested by us and by Pfadt and Lavigne (1965), 3 were effective in eradicating infestations of sheep keds, viz. 1% coumaphos, 2% diazinon, and I % ronnel at recommended rates of power dusting, 2.5-3 Ib/min. Unfortunately none of these are presently labeled. Only 0.5% coumaphos has label approval and is currently recommended (Pfadt et al. 1973). At one time, 2% diazinon sheep dust was labeled but its manufacture was discontinued, perhaps for economic reasons as the less expensive 1.5 dieldrin dust could still be used on sheep. We should point out that 1% diazinon was not tested in any of the power dusting trials; 0.5%
1 Diptera: Hippoboscidae. • Received for publication Mar. 25. 1975. Published with the approval of the Director, Wyoming Agric. Exp. Stn., as Journal Article No. 739. For their assistance in conducting this research the authors gratefully acknowledge the help of F. Henderson, A. Khan, R. Kumar, P. Rosenlund, G. Sharafl, J. Shugart, R. Teuscher, and M. Ullah.
468
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Power dusting of shorn sheep in spring with 1% coumaphos eradicated infestations of Melophagus ovinus (L.) at our recommended application rates of 2.5-3 lbl min. Generally, high reductions but not eradication were provided by coumaphos 0.5%, crotoxyphos 3%, stirofos 3
August
1975
Table I.-Results of power dusting 26 flocks of shorn sheep in spring to control sheep keds.
Before treat· ment
6 wk after treat· ment
'70 reduc· tion
3.1 2.5 2.3 2.1 1.8
97 78 72 66 56
3.0 97.3 23.2 24.5 7.5
0 0 2.4 0.7 0.8
100 100 90 97 89
2.7 2.0
43 31
73.2 14.3
4.4 0.6
94 96
4.1 2.9 2.4 2.0 1.0 1.0
385 259 225 188 94 94
46.1 22.8 7.5 57.3 22.2 15.0
6.4 2.1 2.5 1.6 6.0 5.4
86 91 67 97 73 64
Ronnel I '70
2.0 1.4
63 44
24.7 34.3
1.8 0.8
93 98
Stirofos 5'70
2.1 1.8
93.3 4.9
13.3 0.0
86 100
Stirofos 3%
5.0 3.8 3.2 2.4 1.9 2.2 2.2 3.5 2.3
329 282 470 365 301 225 179 70 70
8.1 1.1 4.2 15.3 19.1 56.6 3.6 4.8 11.6
1.0 0.0 0.3 2.9 1.1
88 100 93 81 94
13.1
77 64
Coumaphos 1'70
Coumaphos 0.5'70 Crotoxyphos 3'70
Stirofos 1'70 Phosmet 1'70 Untreated
Dust· ing rate Ibl min
110 72
Mean no. of keds/heada
11.1 31.2 3.0 50.1
1.3 0.5 2.1 12.3 18.9 1.3 19.9
90 82 -11 39 57 60
• Averages based on total count of sheep ked. on 5 lamb. and 5 ewes from each flock.
was tested, but did not provide eradication; the next concentration was 2% which did. It is probable that Icyo diazinon at rates of 2.5-3 Ib/min would, like coumaphos and ronnel, provide eradication. Evidence from the present research and that of pfadt and DeFoliart (1957), Pfadt (1959), Pfadt and Lavigne (1965), and Taylor et al. (1960) indicates that certain minimum amounts of coumaphos, diazinon, or ronnel applied to sheep as sprays or dusts are required to achieve eradication. The amount of actual insecticide applied to a sheep in a spray race or by power dusting is an estimate based on amount of insecticide expended per head and on careful application of known amounts to individual sheep (Taylor et al. 1960). Our calculations in obtaining estimated amounts applied to power dusted sheep are the following. Sheep pass through the dusting chute at an average rate of 32 head/min. At a dusting rate of 2.5 Ib/min, the amount of dust expended per
=
sheep would be 4 oz +- 32 sheep 1.25 oz or 35.4 g of dust. For a I % dust this represents 0.354 g or 354 mg of actual insecticide. Based on the work of Taylor et al. (1960), an estimated 22% of the dust discharged by a power duster adheres to the sheep. Hence the estimate of the amount of actual insecticide applied to the sheep is 0.22X354 mg = 78.9 mg. With this method, we have included in Table I the estimated amounts of actual insecticide adhering to sheep of the treated flocks. From these data and those of pfadt and Lavigne (1965), we estimate that the minimum effective amounts of actual insecticide applied to shorn sheep in spring are coumaphos 78 mg, diazinon 69 mg. and ronnel 81 mg. In the fall, as wool becomes longer and conditions become more favorable for population increase of sheep keds, the minimum amounts of actual insecticide needed to eradicate infestations increase several fold. Taylor et al. (1960) found that 250 mg of ronnel or diazinon were required on sheep with 3 months of wool growth in New Zealand. The data of Pfadt (1959) and of pfadt and Lavigne (1965) indicate that for sheep with 5-6 months of wool growth, minimum amounts of 250-300 mg of diazinon and 600 mg of ronnel are required to eradicate sheep keds. The 4 organophosphorus insecticides found ineffective in eradicating infestations by power dusting were crotoxyphos, dioxathion. malathion, and stirofos. By hand dusting 5% malathion at rates of I oz/lamb and 2 oz/ewe after shearing in spring and 2 oz/Iamb or ewe in fal!, eradication can be achieved (Pfadt 1959) . This is an approved use of malathion. During the span of 10 years in which we conducted the present sheep dusting trials, cooperating wool growers changed their time of shearing from predominantly after lambing (1964, 1965, 1973) to predominantly before lambing (1974). The process of shearing removes many pupal and adult keds with the wool and many adults are killed by being cut with the shears. A mean of 8.4/head was found on 9 flocks shorn before lambing and a mean of 35.9/head on 20 flocks shorn after lambing. The difference in mean densities represents a total reduction of 77% in sheep ked density among flocks shorn before lambing. Practically all of the difference was due to the greater num· ber of sheep keds on the lambs in the flocks in which ewes were shorn after lambing. In these flocks, the pretreatment mean for lambs was 67.3 (range 18.0181.4) compared to a mean of 4.5 for ewes (range 0-16.2), while for flocks shorn before lambing the means were 9.7 (range 2.6-39.6) and 7.0 (range 014.4), respectively. Evidently substantial numbers of keds transferred from the full fleeced ewes to their lambs and were protected from the hazards of shearing. Nelson (1958) observed that only newly emerged sheep keds transfer from ewes to lambs and that these immature sheep keds begin reproducing and increasing in density after 4-6 wk on the lambs. The average age of lanibs at the time of our sampling of sheep ked densities was 11.4 wk (range 8.6-14.6) for lambs whose dams were shorn before lambing and 14.8 wk
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Esti· mated AI ad· hering per head (mg)
Dust
469
PF ADT ET AL.: POWER DUSTING SHEEP
470
JOURNAL
OF ECONOMIC
(range 7-20.3) for lambs whose dams were shorn after lambing, providing ample time for increase of sheep ked populations. The details of the dynamics of these populations have not been studied and consequently are unknown. Nevertheless, it appears that shearing before lambing is an aid to achieving eradi. cation of infestations when combined with applications of dust by power equipment. REFERENCES CITED Nelson, W. A. 1958. Transfer of sheep keds, MeloPhagus ovinus (L.), from ewes to their lambs. Nature (Lond.) 181: 56.
ENTOMOLOGY
Vol. 68, no. 4
Pfadt, R. E. 1959. Fall dusting to control the sheep ked. J. Econ. Entomol. 52: 380-2. pfadt, R. E., and G. R. DeFoliart. 1957. Power dusting to control the sheep ked. Ibid., 50: 190-4. Pfadt, R. E., and R. J. Lavigne. 1965. Further tests with power dusting to control the sheep ked. Ibid., 58: 37-8. Pfadt, R. E., J. E. lloyd, and E. W. Spackman. 1973. Control of insect and related pests of sheep. Wyo. Agric. Exp. Stn. Bull. 514R. 15 pp. Taylor, R. L., E. M. Oxnam, and W. K. Marris. 1960. Control of lice and keds, a comparison of dieldrin, aldrin, diazinon, and ronnel. N. Z. J. Agric. 100: 119-20.
Downloaded from http://jee.oxfordjournals.org/ by guest on June 7, 2016
Tests of power dusting sheep for control of the sheep ked, Melophagus ovinus (L.), have been continued with organophosphorus insecticides of desirable veterinary characteristics, i.e., low toxicity to mammals and limited residual. Determination of effectiveness of control, the 3rd important characteristic, was the objective of this study. Pfadt and Lavigne (1965) investigated the effectiveness of 5 organophosphorus dusts and I carbamate dust. They found that ked infestations could be eradicated from individual flocks by power dusting with 2% diazinon and I % ronnel, and high reductions of populations achieved by dusting with 0.5% coumaphos, 2% dioxathion, and 4% malathion. Because anything less than eradication permits populations to 'build up during the following fall and winter, our goal was to find insecticides, concentrations, and rates of application of dusts whidl provide this degree of control. In the present tests, we used for the first time dusts of crotoxyphos, phosmet, and stirofos and have repeated testing of coumaphos and ronnel either at different concentrations or at different rates of application. METHODS.-All sheep in a flock were treated with a single insecticide of a given concentration and rate of application to evaluate the performance of the dust. Each dust was tested on at least 2 flocks. AlI sheep in a flock were driven throug'h a curtain of dust generated and expelled by a power duster through outlets in a steel sheep chute (Howry-Berg Sheep Duster). Dusting rates were controlled by a sliding shutter on a circular opening in the bottom of the hopper. The actual dusting rate was calculated by weighing the dust before and after treatment and timing the duration of the dusting period. Sheep ked density was determined by a total count of adults on 5 lambs and 5 ewes of each flock immediately before treatment and again 6 wk later. The interval between examinations provided sufficient time for all pupae present at the time of dusting to emerge as adults. Untreated flocks were examined in the same manner and at the same time interval as treated flocks for comparison. Percen tage reduction of sheep keds,
however, was computed from the pre- and posttreatment counts of each treated flock without use of check mortality. Testing was done on farm flocks in southeast Wyoming. Out of 30 flocks, 24 were white face or white crossed breeds and 6 were black face breeds or white crossed with black. Number of sheep and lambs in flocks ranged from 27-964 and averaged 223. The median sized flock was 108. Flocks were dusted be· tween 15 and 84 days (average 48 days) after shearing in those flocks sheared after lambing and from 69 to III days (avg 86 days) after shearing in those flocks sheared before lambing. RESULTS AND DISCUSSION.-Table I summarizes results of power dusting shorn sheep in spring with 5 organophosphorus insecticides. Although most of the dusts caused significant reduction of sheep ked populations, only a few achieved our goal of eradication. At rates of 2.5 and 3.1 Ib/min, 1% coumaphos provided eradication, but at lower rates, 1.8, 2.1, 2.3 lb/ min, this dust did not provide eradication. Neither did 0.5% coumaphos, which was evaluated at rates of 2.0 and 2.7 lb/min only. Similar results were obtained in previous trials with rates of 3 and 3.5 Ib/ min of 0.5'70 coumaphos (Pfadt and Lavigne 1965). Stirofos of 3% and 5% sometimes provided eradication when populations of sheep keds were low, i.e., I.I and 4.9/head, but generally these dusts were ineffective in eliminating populations completely. Crotoxyphos 3% and phosmet I % did not provide eradication even at high rates of application, 4.1 and 3.5 Ib/min, respectively. At rates of 1.4 and 2 lb/min, 1% ronnel did not achieve eradication, 'but Pfadt and Lavigne (1965) obtained eradication with this dust at rates of 2.6 and 3.3Ib/min. Of 7 organophosphorus insecticides tested by us and by Pfadt and Lavigne (1965), 3 were effective in eradicating infestations of sheep keds, viz. 1% coumaphos, 2% diazinon, and I % ronnel at recommended rates of power dusting, 2.5-3 Ib/min. Unfortunately none of these are presently labeled. Only 0.5% coumaphos has label approval and is currently recommended (Pfadt et al. 1973). At one time, 2% diazinon sheep dust was labeled but its manufacture was discontinued, perhaps for economic reasons as the less expensive 1.5 dieldrin dust could still be used on sheep. We should point out that 1% diazinon was not tested in any of the power dusting trials; 0.5%
1 Diptera: Hippoboscidae. • Received for publication Mar. 25. 1975. Published with the approval of the Director, Wyoming Agric. Exp. Stn., as Journal Article No. 739. For their assistance in conducting this research the authors gratefully acknowledge the help of F. Henderson, A. Khan, R. Kumar, P. Rosenlund, G. Sharafl, J. Shugart, R. Teuscher, and M. Ullah.
468
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Power dusting of shorn sheep in spring with 1% coumaphos eradicated infestations of Melophagus ovinus (L.) at our recommended application rates of 2.5-3 lbl min. Generally, high reductions but not eradication were provided by coumaphos 0.5%, crotoxyphos 3%, stirofos 3
August
1975
Table I.-Results of power dusting 26 flocks of shorn sheep in spring to control sheep keds.
Before treat· ment
6 wk after treat· ment
'70 reduc· tion
3.1 2.5 2.3 2.1 1.8
97 78 72 66 56
3.0 97.3 23.2 24.5 7.5
0 0 2.4 0.7 0.8
100 100 90 97 89
2.7 2.0
43 31
73.2 14.3
4.4 0.6
94 96
4.1 2.9 2.4 2.0 1.0 1.0
385 259 225 188 94 94
46.1 22.8 7.5 57.3 22.2 15.0
6.4 2.1 2.5 1.6 6.0 5.4
86 91 67 97 73 64
Ronnel I '70
2.0 1.4
63 44
24.7 34.3
1.8 0.8
93 98
Stirofos 5'70
2.1 1.8
93.3 4.9
13.3 0.0
86 100
Stirofos 3%
5.0 3.8 3.2 2.4 1.9 2.2 2.2 3.5 2.3
329 282 470 365 301 225 179 70 70
8.1 1.1 4.2 15.3 19.1 56.6 3.6 4.8 11.6
1.0 0.0 0.3 2.9 1.1
88 100 93 81 94
13.1
77 64
Coumaphos 1'70
Coumaphos 0.5'70 Crotoxyphos 3'70
Stirofos 1'70 Phosmet 1'70 Untreated
Dust· ing rate Ibl min
110 72
Mean no. of keds/heada
11.1 31.2 3.0 50.1
1.3 0.5 2.1 12.3 18.9 1.3 19.9
90 82 -11 39 57 60
• Averages based on total count of sheep ked. on 5 lamb. and 5 ewes from each flock.
was tested, but did not provide eradication; the next concentration was 2% which did. It is probable that Icyo diazinon at rates of 2.5-3 Ib/min would, like coumaphos and ronnel, provide eradication. Evidence from the present research and that of pfadt and DeFoliart (1957), Pfadt (1959), Pfadt and Lavigne (1965), and Taylor et al. (1960) indicates that certain minimum amounts of coumaphos, diazinon, or ronnel applied to sheep as sprays or dusts are required to achieve eradication. The amount of actual insecticide applied to a sheep in a spray race or by power dusting is an estimate based on amount of insecticide expended per head and on careful application of known amounts to individual sheep (Taylor et al. 1960). Our calculations in obtaining estimated amounts applied to power dusted sheep are the following. Sheep pass through the dusting chute at an average rate of 32 head/min. At a dusting rate of 2.5 Ib/min, the amount of dust expended per
=
sheep would be 4 oz +- 32 sheep 1.25 oz or 35.4 g of dust. For a I % dust this represents 0.354 g or 354 mg of actual insecticide. Based on the work of Taylor et al. (1960), an estimated 22% of the dust discharged by a power duster adheres to the sheep. Hence the estimate of the amount of actual insecticide applied to the sheep is 0.22X354 mg = 78.9 mg. With this method, we have included in Table I the estimated amounts of actual insecticide adhering to sheep of the treated flocks. From these data and those of pfadt and Lavigne (1965), we estimate that the minimum effective amounts of actual insecticide applied to shorn sheep in spring are coumaphos 78 mg, diazinon 69 mg. and ronnel 81 mg. In the fall, as wool becomes longer and conditions become more favorable for population increase of sheep keds, the minimum amounts of actual insecticide needed to eradicate infestations increase several fold. Taylor et al. (1960) found that 250 mg of ronnel or diazinon were required on sheep with 3 months of wool growth in New Zealand. The data of Pfadt (1959) and of pfadt and Lavigne (1965) indicate that for sheep with 5-6 months of wool growth, minimum amounts of 250-300 mg of diazinon and 600 mg of ronnel are required to eradicate sheep keds. The 4 organophosphorus insecticides found ineffective in eradicating infestations by power dusting were crotoxyphos, dioxathion. malathion, and stirofos. By hand dusting 5% malathion at rates of I oz/lamb and 2 oz/ewe after shearing in spring and 2 oz/Iamb or ewe in fal!, eradication can be achieved (Pfadt 1959) . This is an approved use of malathion. During the span of 10 years in which we conducted the present sheep dusting trials, cooperating wool growers changed their time of shearing from predominantly after lambing (1964, 1965, 1973) to predominantly before lambing (1974). The process of shearing removes many pupal and adult keds with the wool and many adults are killed by being cut with the shears. A mean of 8.4/head was found on 9 flocks shorn before lambing and a mean of 35.9/head on 20 flocks shorn after lambing. The difference in mean densities represents a total reduction of 77% in sheep ked density among flocks shorn before lambing. Practically all of the difference was due to the greater num· ber of sheep keds on the lambs in the flocks in which ewes were shorn after lambing. In these flocks, the pretreatment mean for lambs was 67.3 (range 18.0181.4) compared to a mean of 4.5 for ewes (range 0-16.2), while for flocks shorn before lambing the means were 9.7 (range 2.6-39.6) and 7.0 (range 014.4), respectively. Evidently substantial numbers of keds transferred from the full fleeced ewes to their lambs and were protected from the hazards of shearing. Nelson (1958) observed that only newly emerged sheep keds transfer from ewes to lambs and that these immature sheep keds begin reproducing and increasing in density after 4-6 wk on the lambs. The average age of lanibs at the time of our sampling of sheep ked densities was 11.4 wk (range 8.6-14.6) for lambs whose dams were shorn before lambing and 14.8 wk
Downloaded from http://jee.oxfordjournals.org/ by guest on June 7, 2016
Esti· mated AI ad· hering per head (mg)
Dust
469
PF ADT ET AL.: POWER DUSTING SHEEP
470
JOURNAL
OF ECONOMIC
(range 7-20.3) for lambs whose dams were shorn after lambing, providing ample time for increase of sheep ked populations. The details of the dynamics of these populations have not been studied and consequently are unknown. Nevertheless, it appears that shearing before lambing is an aid to achieving eradi. cation of infestations when combined with applications of dust by power equipment. REFERENCES CITED Nelson, W. A. 1958. Transfer of sheep keds, MeloPhagus ovinus (L.), from ewes to their lambs. Nature (Lond.) 181: 56.
ENTOMOLOGY
Vol. 68, no. 4
Pfadt, R. E. 1959. Fall dusting to control the sheep ked. J. Econ. Entomol. 52: 380-2. pfadt, R. E., and G. R. DeFoliart. 1957. Power dusting to control the sheep ked. Ibid., 50: 190-4. Pfadt, R. E., and R. J. Lavigne. 1965. Further tests with power dusting to control the sheep ked. Ibid., 58: 37-8. Pfadt, R. E., J. E. lloyd, and E. W. Spackman. 1973. Control of insect and related pests of sheep. Wyo. Agric. Exp. Stn. Bull. 514R. 15 pp. Taylor, R. L., E. M. Oxnam, and W. K. Marris. 1960. Control of lice and keds, a comparison of dieldrin, aldrin, diazinon, and ronnel. N. Z. J. Agric. 100: 119-20.
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