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Effectiveness of a synthetic lure to reduce blowfly strike incidence: preliminary observations
Veterinary Parasitology 97 (2001) 77–82
Effectiveness of a synthetic lure to reduce blowfly strike incidence: preliminary observations Michael P. Ward∗ Queensland Department of Primary Industries, Animal Research Institute, Locked Mail Bag 4, Moorooka, Qld 4105, Australia Received 2 January 2001
Abstract The effectiveness of a synthetic lure system (Lucitrap® ) to reduce blowfly strike incidence was assessed in a field trial conducted on two properties located in southern Queensland, Australia. Nine hundred and fifty sheep were randomised to treatment (one or more Lucitrap® per 100 sheep) and control paddocks. Sheep were physically inspected for flystrike each month between August 1999 and May 2000. On one property, the risk of flystrike in the control group was 1.86 times (95% confidence interval, 1.19–2.90) greater than that in the treatment group. On the other property, two cases of flystrike were detected in the control group, but no cases were detected in the treatment group. These preliminary observations suggest that the use of Lucitrap® can reduce the incidence of blowfly strike by up to about one-half. Blowfly traps have a role in controlling flystrike in circumstances in which sheep are susceptible to flystrike and the likelihood of flystrike occurring is at least moderate. The use of fly traps could assist the Australian wool industry to meet targets of reduced pesticide use. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Lucilia cuprina; Blowfly strike; Sheep–Arthropoda; Trap; Trial; Australia
1. Introduction Blowfly strike is estimated to cost the Australian sheep industry at least AUS$ 161 million annually (McLeod, 1995). Whilst the use of pesticides to prevent blowfly strike is cost-effective, increasing concern regarding pesticide residues on wool and environmental and occupational health and safety consequences has prompted the need to minimise pesticide use through development of integrated parasite control programs (Tellam and Bowles, ∗ Present address: Department of Veterinary Pathobiology, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907-1243, USA. Tel.: +1-765-494-5796; fax: +1-765-494-9830. E-mail address: [email protected] (M.P. Ward).
0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 0 1 ) 0 0 3 7 7 - 6
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M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
1997; Karlsson, 1999). Such programs rely on more than one (and preferably several) methods acting synergistically to control parasite populations, reducing the total amount of pesticide used. Control of blowfly strike relies on both suppressing blowfly populations and reducing susceptibility of sheep to blowfly strike. Several management practices are used to reduce sheep susceptibility, such as mulesing, crutching, tail docking, strategic shearing, internal parasite control, breeding for resistance (Watts et al., 1979). Development of vaccines against flystrike and fleece rot have been attempted (Tellam and Bowles, 1997). Attempts have also been made to forecast the occurrence of flystrike in sheep flocks, based on climatic parameters, in order to assist decision-making by wool producers with respect to flystrike control options (Ward, 2000). The ability to accurately predict periods of increased flystrike risk would assist wool producers to control flystrike more effectively, for example through increased monitoring and the judicious use of a variety of control methods (Ward, 2001). Suppression of blowfly populations has focused on fly traps and genetic control. Liver/sodium sulphide combinations (bait bins) have been used in the Australian sheep industry for many years (Mackerras et al., 1936; Anderson et al., 1990). These may reduce flystrike, but servicing traps is labour-intensive. A synthetic lure, consisting of kairomones, was developed in the early 1990s (Urech et al., 1993), and a trap using this lure was released commercially in 1994 as Lucitrap® (Miazma Pty Ltd, 3 Acacia Court, Mt. Crosby, Queensland 4306). Unlike bait bins, the Lucitrap® system requires minimal ongoing labour input. Also, lures are more attractive and specific for Lucilia cuprina, responsible for 80 to 90% of flystrike in Australian sheep flocks. Whilst the effectiveness of the Lucitrap system in reducing blowfly populations has been demonstrated (Urech et al., 1993), its effectiveness in reducing blowfly strike has not. A 3-year project to evaluate the use of Lucitrap® by woolgrower groups to reduce pesticide use commenced in 1998. A component of this project is to determine whether Lucitrap® use reduces the incidence of blowfly strike. Results of field studies conducted from 1999 to 2000 are reported in this paper.
2. Materials and methods Two properties (A and B) located in southern Queensland approximately 200 km southwest of Brisbane and 250 north of Armidale were selected. The district lies between 600 and 700 m above sea level and receives 700 mm annual rainfall. Pastures are predominantly native grass species. The study properties, situated 15 km apart, were managed by members of a group of woolgrowers that had used Lucitrap® since 1994. The Lucitrap® product is shown in Fig. 1. On both properties, treatment paddocks were identified in which traps (Lucitrap® ) were operated and that adjoined other paddocks (either the same property or a neighbouring property) in which traps were also operated. Control paddocks were identified in which traps were not operated and adjoined a neighbouring paddock (either the same property or a neighbouring property) in which traps were also not operated. Treatment and control paddocks were located approximately 3 and 1 km apart on Property A and B, respectively. Treatment and control paddocks were stocked with Merino-cross sheep at a stocking rate of approximately 2.5 per hectare. In July 1999, sheep were randomly allocated to paddocks from the same mob (weaner ewes aged approximately 10 months on
M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
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Fig. 1. Lucitrap® (Miazma Pty Ltd, 3 Acacia Court, Mt. Crosby, Queensland 4306), a blowfly trapping system based on a synthetic lure, in operation.
Property A, and wethers aged 2 to 3 years on Property B). Traps were operated following manufacturer’s recommendations: four and two traps were operated in treatment paddocks on Properties A and B, respectively (one or more traps per 100 sheep), and traps were recharged with lure every 3 months during the trial. Between August 1999 and May 2000, sheep on both Property A and B were mustered and inspected at monthly intervals by the same technical assistant, and managers were requested to observe sheep more closely than usual during the study period. When a flystrike was detected, the age of the lesion (based on size and depth) was determined so that the likely time of initiation of the strike could be estimated. The lesion was treated by clipping surrounding wool and applying a flystrike dressing containing diazinon. The risk of flystrike within each treatment and control group was calculated using the number of flystrike cases as the numerator, and the number of sheep-days at-risk as the denominator. If a sheep was struck, it was assumed to be no longer at-risk of flystrike during the study period since resistance to flystrike may occur following exposure to L. cuprina larvae (Watts, 1979). Incidence of flystrike in treatment and control
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M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
groups on each property was compared by estimating relative risk and 95% confidence intervals (Win Episcope version 2, Epidecon, Zaragoza, 1998). The number and species of blowflies caught in traps was not recorded, because predation by ants prevents accurate counts being made (Horton et al., 1999). A total of 950 sheep were enrolled, 550 on Property A and 400 on Property B. On Property A, treatment and control groups consisted of 350 and 200 sheep, respectively, and on Property B treatment and control groups consisted of 200 sheep each.
3. Results Seventy-seven (14%) cases of flystrike were observed within the study groups on Property A between August and November 1999. All except one case occurred during the last week of October or first week of November. During October, 173 mm of rainfall was recorded in the study area, representing approximately 25% of the district annual average and nearly three times the average rainfall for the month of October. Cases were predominantly shoulder strike and were overt. The trial on Property A was suspended in November 1999 because of preset animal welfare criteria and all sheep were treated with cyromazine (VetrazinTM ; Novartis). The trial recommenced in February 2000 after the persistency of affect of cyromazine ended (Bowen et al., 1999). During the observation period (August to November 1999 and February to May 2000), a total of 18,613 and 37,368 sheep-days at-risk were accumulated in control and treatment groups, respectively, and 37 and 40 cases of flystrike were detected. The risk of flystrike in the control group was 1.86 times (95% confidence interval, 1.19–2.90) greater than in the treatment group. Between August 1999 and May 2000, two cases of flystrike were detected in the control group on Property B, but no cases were detected in the treatment group. A total of 56,816 and 57,200 sheep-days at-risk were accumulated in control and treatment groups, respectively, during the period of observation. The species of blowfly striking sheep in this trial were not determined.
4. Discussion Demonstrating the effectiveness of blowfly strike preventive measures that are applied to groups of sheep under field conditions presents methodological difficulties (Bowen et al., 1999; Schmid et al., 1999). Flystrike occurrence can be highly variable both within a season and from year-to-year, and identifying appropriate study sites presents challenges. In particular, studies must be conducted at sites where similar sheep can be randomised to treatment and control paddocks and managed identically, yet where paddocks have a similar initial blowfly population and are sufficiently separated so that the possibility of blowfly migration is minimised. The two properties selected fitted this criteria. The problem of insufficient fly challenge at a particular study site is not uncommon in field trials (Bowen et al., 1999). Both properties in this trial had been monitored for flystrike between August 1998 and April 1999 (Ward, unpublished data). Estimates of flystrike on Properties A and B were 31 and 2%, respectively. In the trial, flystrike rates of 18.5 and 1%, respectively, were observed in control groups. Thus flystrike challenge in 1999/2000 was not as great as in the
M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
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previous season, but the rates of strike remained similar in control groups, indicating that estimates of flystrike in control paddocks provided a valid comparison for the effectiveness of Lucitrap® in reducing flystrike incidence. Control and treatment paddocks were located approximately 1 to 3 km apart. In Queensland, blowflies have been found to congregate around areas of water and sheep camps, with few flies trapped more than 1 to 2 km from these loci (O’Sullivan et al., 1983). Although the possibility of blowflies migrating from control to treatment paddocks cannot be ruled-out in the current trial, it seems unlikely based on the known ecology of L. cuprina. Also, such migration would tend to reduce the effectiveness of Lucitrap® , making it even more difficult to demonstrate a significant reduction in flystrike incidence. Study results suggest that Lucitrap® use was associated with a reduction in flystrike of 46% on Property A. Insufficient blowfly strike occurred on Property B to test the effectiveness of Lucitrap® . These results demonstrate the variability that may be observed in flystrike occurrence. Variability may occur due to annual changes in blowfly populations, innate resistance of sheep to flystrike and resistance due to elective management procedures such as crutching, the mules operation and pesticide application. Management procedures were controlled in this trial through randomisation of sheep to study groups and management of treatment and control groups in an identical manner. Since the properties in this study were separated by only approximately 15 km, seasonal conditions were very similar during the study period. Therefore, the difference in flystrike occurrence between study sheep located on Properties A and B was likely caused by differences in innate resistance to flystrike. Variability between groups of sheep in their resistance to flystrike has been attributed to gender, body conformation and fleece characteristics (Watts et al., 1979). Results indicate that trial sheep (weaner ewes aged approximately 10 months) on Property A were susceptible to flystrike, whereas trial sheep (wethers aged 2 to 3 years) on Property B were resistant. This variability is a feature of sheep production in Australia (Vogt and Woodburn, 1979). The reduction (46%) in flystrike observed on Property A in this trial is not sufficient to control flystrike in sheep flocks, and does not compare with the magnitude of reduction that can be achieved using new generation pesticides, such as dicyclanil (Schmid et al., 1999). However, if trap use is integrated with other management procedures effective control of flystrike may be possible without the need to use pesticides. This would be of major benefit to the Australian wool industry, which is attempting to reduce pesticide use (Williams and Brightling, 1999). Based on study results, long-term use of traps may reduce pesticide use. Although most pesticide applications for blowfly control probably do not result in unacceptable pesticide residues on wool, a substantial proportion of woolgrowers apply pesticides (for a variety of reasons) too close to wool harvesting, resulting in unacceptable residue levels on wool (Ward and Armstrong, 1998). Use of fly traps will be most effective in reducing pesticide residue levels in Australian wool if these late season applications can be avoided.
Acknowledgements The author gratefully acknowledges the assistance of woolgrowers who provided sheep and facilities to conduct this study. Support for this study was provided by Australian
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woolgrowers and the Australian Government through the Australian Wool Research and Promotion Organisation. Trial design and conduct was approved by the Department of Primary Industries South Region Local Animal Ethics Committee (SLAEC-DPI-016). References Anderson, J.M.E., McLeod, L.J., Shipp, E., Swan, A., Kennedy, J.P., 1990. Trapping sheep blowflies using bait-bins. Aust. Vet. J. 67, 93–97. Bowen, F.L., Fisara, P., Junquera, P., Keevers, D.T., Mahoney, R.H., Schmid, H.R., 1999. Long-lasting prevention against blowfly strike using the insect growth regulator dicyclanil. Aust. Vet. J. 77, 454–460. Horton, J.D., Champion, S.C., Horton, B.J., 1999. Development of a simple method to assess the number of Lucilia cuprina caught in Lucitrap® fly traps. Wool Tech. Sheep. Breed. 47, 74–82. Karlsson, L.J.E., 1999. Sustainable sheep ectoparasitic control using IPM. In: Besier, B. (Ed.), Proceedings of the Australian Sheep Veterinary Society, AVA, Hobart, pp. 128–133. McLeod, R.S., 1995. Costs of major parasites to the Australian livestock industries. Int. J. Parasitol. 25, 1363–1367. Mackerras, I.M., Fuller, M.E., Austin, K.M., Lefroy, E.H.B., 1936. Sheep blowfly investigations. The effect of trapping on the incidence of strike in sheep. J. Council Sci. Ind. Res. 9, 153–162. O’Sullivan, B.M., Perkins, I., Vokes, L., Suter, G., Hopkins, P.S., 1983. The ecology of Lucilia cuprina (Wiedemann) in western Queensland. In: Second National Symposium on the Sheep Blowfly and Flystrike in Sheep, University of New South Wales, Sydney. Department of Agriculture, NSW, pp. 96–99. Schmid, H.R., van Tulder, G., Junquera, P., 1999. Field efficacy of the insect growth regulator dicyclanil for flystrike prevention on lambs. Vet. Parasitol. 86, 147–151. Tellam, R.L., Bowles, V.M., 1997. Control of blowfly strike in sheep: current strategies and future prospects. Int. J. Parasitol. 27, 261–273. Urech, R., Green, P.E., Rice, M.J., Brown, G.W., Duncalfe, E., Webb, P.D., Pritchard, D.A., 1993. Field performance of synthetic lures for the Australian sheep blowfly Lucilia cuprina (Diptera: Calliphoridae). In: Corey, S.A., Dall, D.J., Milne, W.M. (Eds.), Pest Control and Sustainable Agriculture. Commonwealth Scientific and Industrial Research Organisation, Melbourne, pp. 277–279. Vogt, W.G., Woodburn, T.L., 1979. Ecology, distribution and importance of sheep myiasis flies in Australia. In: National Symposium on the Sheep Blowfly and Flystrike in Sheep. Department of Agriculture, Sydney, NSW, pp. 23–32. Ward, M.P., 2000. Forecasting blowfly strike in Queensland sheep flocks. Vet. Parasitol. 92, 309–317. Ward, M.P., 2001. Use of interpolated climatic parameters to predict risk of blowfly strike in Queensland sheep flocks. Prev. Vet. Med. 49, 115–124. Ward, M.P., Armstrong, R.T.F., 1998. Pesticide use and residues on Queensland wool. Aust. Vet. J. 76, 739–742. Watts, J.E., 1979. Body strike of sheep. In: National Symposium on the Sheep Blowfly and Flystrike in Sheep. Department of Agriculture, Sydney, NSW, pp. 23–32. Watts, J.E., Murray, M.D., Graham, N.P.H., 1979. The blowfly strike problem of sheep in New South Wales. Aust. Vet. J. 55, 325–334. Williams, S.H, Brightling, A., 1999. The Australian wool industry’s response to the issue of pesticides residues. In: Besier, B. (Ed.), Proceedings of the Australian Sheep Veterinarian Society Conference, Hobart, pp. 77–84.
Effectiveness of a synthetic lure to reduce blowfly strike incidence: preliminary observations Michael P. Ward∗ Queensland Department of Primary Industries, Animal Research Institute, Locked Mail Bag 4, Moorooka, Qld 4105, Australia Received 2 January 2001
Abstract The effectiveness of a synthetic lure system (Lucitrap® ) to reduce blowfly strike incidence was assessed in a field trial conducted on two properties located in southern Queensland, Australia. Nine hundred and fifty sheep were randomised to treatment (one or more Lucitrap® per 100 sheep) and control paddocks. Sheep were physically inspected for flystrike each month between August 1999 and May 2000. On one property, the risk of flystrike in the control group was 1.86 times (95% confidence interval, 1.19–2.90) greater than that in the treatment group. On the other property, two cases of flystrike were detected in the control group, but no cases were detected in the treatment group. These preliminary observations suggest that the use of Lucitrap® can reduce the incidence of blowfly strike by up to about one-half. Blowfly traps have a role in controlling flystrike in circumstances in which sheep are susceptible to flystrike and the likelihood of flystrike occurring is at least moderate. The use of fly traps could assist the Australian wool industry to meet targets of reduced pesticide use. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Lucilia cuprina; Blowfly strike; Sheep–Arthropoda; Trap; Trial; Australia
1. Introduction Blowfly strike is estimated to cost the Australian sheep industry at least AUS$ 161 million annually (McLeod, 1995). Whilst the use of pesticides to prevent blowfly strike is cost-effective, increasing concern regarding pesticide residues on wool and environmental and occupational health and safety consequences has prompted the need to minimise pesticide use through development of integrated parasite control programs (Tellam and Bowles, ∗ Present address: Department of Veterinary Pathobiology, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907-1243, USA. Tel.: +1-765-494-5796; fax: +1-765-494-9830. E-mail address: [email protected] (M.P. Ward).
0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 0 1 ) 0 0 3 7 7 - 6
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M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
1997; Karlsson, 1999). Such programs rely on more than one (and preferably several) methods acting synergistically to control parasite populations, reducing the total amount of pesticide used. Control of blowfly strike relies on both suppressing blowfly populations and reducing susceptibility of sheep to blowfly strike. Several management practices are used to reduce sheep susceptibility, such as mulesing, crutching, tail docking, strategic shearing, internal parasite control, breeding for resistance (Watts et al., 1979). Development of vaccines against flystrike and fleece rot have been attempted (Tellam and Bowles, 1997). Attempts have also been made to forecast the occurrence of flystrike in sheep flocks, based on climatic parameters, in order to assist decision-making by wool producers with respect to flystrike control options (Ward, 2000). The ability to accurately predict periods of increased flystrike risk would assist wool producers to control flystrike more effectively, for example through increased monitoring and the judicious use of a variety of control methods (Ward, 2001). Suppression of blowfly populations has focused on fly traps and genetic control. Liver/sodium sulphide combinations (bait bins) have been used in the Australian sheep industry for many years (Mackerras et al., 1936; Anderson et al., 1990). These may reduce flystrike, but servicing traps is labour-intensive. A synthetic lure, consisting of kairomones, was developed in the early 1990s (Urech et al., 1993), and a trap using this lure was released commercially in 1994 as Lucitrap® (Miazma Pty Ltd, 3 Acacia Court, Mt. Crosby, Queensland 4306). Unlike bait bins, the Lucitrap® system requires minimal ongoing labour input. Also, lures are more attractive and specific for Lucilia cuprina, responsible for 80 to 90% of flystrike in Australian sheep flocks. Whilst the effectiveness of the Lucitrap system in reducing blowfly populations has been demonstrated (Urech et al., 1993), its effectiveness in reducing blowfly strike has not. A 3-year project to evaluate the use of Lucitrap® by woolgrower groups to reduce pesticide use commenced in 1998. A component of this project is to determine whether Lucitrap® use reduces the incidence of blowfly strike. Results of field studies conducted from 1999 to 2000 are reported in this paper.
2. Materials and methods Two properties (A and B) located in southern Queensland approximately 200 km southwest of Brisbane and 250 north of Armidale were selected. The district lies between 600 and 700 m above sea level and receives 700 mm annual rainfall. Pastures are predominantly native grass species. The study properties, situated 15 km apart, were managed by members of a group of woolgrowers that had used Lucitrap® since 1994. The Lucitrap® product is shown in Fig. 1. On both properties, treatment paddocks were identified in which traps (Lucitrap® ) were operated and that adjoined other paddocks (either the same property or a neighbouring property) in which traps were also operated. Control paddocks were identified in which traps were not operated and adjoined a neighbouring paddock (either the same property or a neighbouring property) in which traps were also not operated. Treatment and control paddocks were located approximately 3 and 1 km apart on Property A and B, respectively. Treatment and control paddocks were stocked with Merino-cross sheep at a stocking rate of approximately 2.5 per hectare. In July 1999, sheep were randomly allocated to paddocks from the same mob (weaner ewes aged approximately 10 months on
M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
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Fig. 1. Lucitrap® (Miazma Pty Ltd, 3 Acacia Court, Mt. Crosby, Queensland 4306), a blowfly trapping system based on a synthetic lure, in operation.
Property A, and wethers aged 2 to 3 years on Property B). Traps were operated following manufacturer’s recommendations: four and two traps were operated in treatment paddocks on Properties A and B, respectively (one or more traps per 100 sheep), and traps were recharged with lure every 3 months during the trial. Between August 1999 and May 2000, sheep on both Property A and B were mustered and inspected at monthly intervals by the same technical assistant, and managers were requested to observe sheep more closely than usual during the study period. When a flystrike was detected, the age of the lesion (based on size and depth) was determined so that the likely time of initiation of the strike could be estimated. The lesion was treated by clipping surrounding wool and applying a flystrike dressing containing diazinon. The risk of flystrike within each treatment and control group was calculated using the number of flystrike cases as the numerator, and the number of sheep-days at-risk as the denominator. If a sheep was struck, it was assumed to be no longer at-risk of flystrike during the study period since resistance to flystrike may occur following exposure to L. cuprina larvae (Watts, 1979). Incidence of flystrike in treatment and control
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M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
groups on each property was compared by estimating relative risk and 95% confidence intervals (Win Episcope version 2, Epidecon, Zaragoza, 1998). The number and species of blowflies caught in traps was not recorded, because predation by ants prevents accurate counts being made (Horton et al., 1999). A total of 950 sheep were enrolled, 550 on Property A and 400 on Property B. On Property A, treatment and control groups consisted of 350 and 200 sheep, respectively, and on Property B treatment and control groups consisted of 200 sheep each.
3. Results Seventy-seven (14%) cases of flystrike were observed within the study groups on Property A between August and November 1999. All except one case occurred during the last week of October or first week of November. During October, 173 mm of rainfall was recorded in the study area, representing approximately 25% of the district annual average and nearly three times the average rainfall for the month of October. Cases were predominantly shoulder strike and were overt. The trial on Property A was suspended in November 1999 because of preset animal welfare criteria and all sheep were treated with cyromazine (VetrazinTM ; Novartis). The trial recommenced in February 2000 after the persistency of affect of cyromazine ended (Bowen et al., 1999). During the observation period (August to November 1999 and February to May 2000), a total of 18,613 and 37,368 sheep-days at-risk were accumulated in control and treatment groups, respectively, and 37 and 40 cases of flystrike were detected. The risk of flystrike in the control group was 1.86 times (95% confidence interval, 1.19–2.90) greater than in the treatment group. Between August 1999 and May 2000, two cases of flystrike were detected in the control group on Property B, but no cases were detected in the treatment group. A total of 56,816 and 57,200 sheep-days at-risk were accumulated in control and treatment groups, respectively, during the period of observation. The species of blowfly striking sheep in this trial were not determined.
4. Discussion Demonstrating the effectiveness of blowfly strike preventive measures that are applied to groups of sheep under field conditions presents methodological difficulties (Bowen et al., 1999; Schmid et al., 1999). Flystrike occurrence can be highly variable both within a season and from year-to-year, and identifying appropriate study sites presents challenges. In particular, studies must be conducted at sites where similar sheep can be randomised to treatment and control paddocks and managed identically, yet where paddocks have a similar initial blowfly population and are sufficiently separated so that the possibility of blowfly migration is minimised. The two properties selected fitted this criteria. The problem of insufficient fly challenge at a particular study site is not uncommon in field trials (Bowen et al., 1999). Both properties in this trial had been monitored for flystrike between August 1998 and April 1999 (Ward, unpublished data). Estimates of flystrike on Properties A and B were 31 and 2%, respectively. In the trial, flystrike rates of 18.5 and 1%, respectively, were observed in control groups. Thus flystrike challenge in 1999/2000 was not as great as in the
M.P. Ward / Veterinary Parasitology 97 (2001) 77–82
81
previous season, but the rates of strike remained similar in control groups, indicating that estimates of flystrike in control paddocks provided a valid comparison for the effectiveness of Lucitrap® in reducing flystrike incidence. Control and treatment paddocks were located approximately 1 to 3 km apart. In Queensland, blowflies have been found to congregate around areas of water and sheep camps, with few flies trapped more than 1 to 2 km from these loci (O’Sullivan et al., 1983). Although the possibility of blowflies migrating from control to treatment paddocks cannot be ruled-out in the current trial, it seems unlikely based on the known ecology of L. cuprina. Also, such migration would tend to reduce the effectiveness of Lucitrap® , making it even more difficult to demonstrate a significant reduction in flystrike incidence. Study results suggest that Lucitrap® use was associated with a reduction in flystrike of 46% on Property A. Insufficient blowfly strike occurred on Property B to test the effectiveness of Lucitrap® . These results demonstrate the variability that may be observed in flystrike occurrence. Variability may occur due to annual changes in blowfly populations, innate resistance of sheep to flystrike and resistance due to elective management procedures such as crutching, the mules operation and pesticide application. Management procedures were controlled in this trial through randomisation of sheep to study groups and management of treatment and control groups in an identical manner. Since the properties in this study were separated by only approximately 15 km, seasonal conditions were very similar during the study period. Therefore, the difference in flystrike occurrence between study sheep located on Properties A and B was likely caused by differences in innate resistance to flystrike. Variability between groups of sheep in their resistance to flystrike has been attributed to gender, body conformation and fleece characteristics (Watts et al., 1979). Results indicate that trial sheep (weaner ewes aged approximately 10 months) on Property A were susceptible to flystrike, whereas trial sheep (wethers aged 2 to 3 years) on Property B were resistant. This variability is a feature of sheep production in Australia (Vogt and Woodburn, 1979). The reduction (46%) in flystrike observed on Property A in this trial is not sufficient to control flystrike in sheep flocks, and does not compare with the magnitude of reduction that can be achieved using new generation pesticides, such as dicyclanil (Schmid et al., 1999). However, if trap use is integrated with other management procedures effective control of flystrike may be possible without the need to use pesticides. This would be of major benefit to the Australian wool industry, which is attempting to reduce pesticide use (Williams and Brightling, 1999). Based on study results, long-term use of traps may reduce pesticide use. Although most pesticide applications for blowfly control probably do not result in unacceptable pesticide residues on wool, a substantial proportion of woolgrowers apply pesticides (for a variety of reasons) too close to wool harvesting, resulting in unacceptable residue levels on wool (Ward and Armstrong, 1998). Use of fly traps will be most effective in reducing pesticide residue levels in Australian wool if these late season applications can be avoided.
Acknowledgements The author gratefully acknowledges the assistance of woolgrowers who provided sheep and facilities to conduct this study. Support for this study was provided by Australian
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