Strategic use of, and alternatives to, chemicals for the control.

Abstract

Proc. Aust. Soc. Anim. Prod, Vol. 18 STRATEGIC USE OF, AND ALTERNATIVES TO, CHEMICALS FOR THE CONTROL OF ARTHROPOD PESTS OF LIVESTOCK P. J. JAMES* To address increasing consumer concern over the potential for pesticide residues in farm produce, as well as other problems associated with pesticide usage, it is important that the livestock industries utilize integrated programmes which maximise the efficiency of use of pesticides. Effective integrated programmes are available for the control of many livestock pests but often the non-chemical components are under utilized. Biological, genetic, and immunological means of control, breeding for improved resistance. and improved strategies for the administration of chemicals for the control of Australian livestock pests are discussed, Education of consumers of the rigorous safety standards required for registration of veterinary chemicals and of the low potential for residues from modern ectoparasiticides should be a priority. INTRODUCTION attention on residues from ectoparasiticides has to date focused on two main groups, the organochlorines and arsenic. Industry bodies have been quick to act. The sale of these compounds for controlling any species of livestock parasites has been banned and monitoring systems to check for residues in meat, wool, milk and eggs are now in place. This paper is not concerned with these chemicals. However, currently there seems to be a perception in the community that use of all synthetic pesticides is bad and the presence of residues of any sort is unacceptable. Most Regardless of whether the fears expressed are real or imagined, residues, even though they may be well within acceptable limits, can affect the marketability of produce. As a major exporter of livestock such considerations are crucially important to the Australian economy. the interests of all livestock industries to develop parasite strategies which avoid chemical residues in livestock, products.. _. pesticide severely products It is in control In addition, strategic use of ectoparasiticides is important for the following reasons: 1. Pesticide resistance - Already resistance has caused problems for the control of many ectoparasite species (Drummond 1977). When resistance develops, higher concentrations of pesticide are required to achieve control and the chance of residues is increased, With stricter controls and burgeoning costs to develop and register new products it is likely that there will be a reduction in the rate of release of new pesticides onto the market. It is important that usage patterns be adopted to minimise selection for resistance and maximise the effective life of those pesticides presently available, Occupational exposure to pesticides - Farm workers applying treatments as well as personnel employed in other sectors of the industry such as shearers, stockmen and slaughtermen may be exposed to pesticides. Protocols are currently being developed for the assessment of hazard from pesticide residues in raw wool (Reed et al. 1989). Environmental considerations - Effects on non-target organisms, accumulation of residues in the environment and disposal of pesticide Department of Agriculture, G.P.0. Box 1671, Adelaide, S.A. 5001. 37 2. - -. 3. * Proc. Aust. Soc. Anim. Prod. vol. 18 wastes are increasingly topics of public concern. 4. Economic considerations - Optimising the effect of each treatment will reduce both the number of treatments required and the associated labour and chemical costs. and the chance of Ways in which the use of pesticides can be optimised pesticide residues minimised are discussed in this paper. RESIDUESFROM CURRENLY REGISTERED ECTOPAFUJSITICIDES Prior to registration of a pesticide for the treatment of livestock, maximum residue limits (MRLs), which incorporate a large safety factor, are carefully established for residual levels in meat, milk and eggs. MRLs should no be exceeded if pesticides are applied according to label directions and the withholding periods are observed. Most ectoparasiticides currently registered, if absorbed into body tissues at all, are rapidly detoxif Fed and excreted. A number have zero withholding periods. Table 1 Residues of chemicals which are currently registered for the treatment of ectoparasites on domestic livestock - National Residue Survey July 1988 to June 1989 Data in Table 1 show the residues detected in livestock meats, eggs and milk in the National Residue Survey during the 1988/89 year that could possibly have resulted from treatments for ectoparasite control. Of a total of 25,706 samples tested, only 4 (0.016%) exceeded permissable MRLs while 0.26% contained detectable levels of residues below the MRL. Seneviratna and Baton (198-9) note that sheep fed grain treated with fenitrothion or chlorpyriphos, which are extensively used to protect grain from store product pests, can show violative levels for organophosphates if slaughtered within a few days of feeding, Some residues for organophosphates may have resulted from ingestion of contaminated 38 Proc. Aust, Soc. Anim. Prod. Vol. 18 food rather than from use of ectoparasiticides, Of the samples which exceeded -0, those for ivermectin and avermectin resulted from the use of these pesticides on species for which they were not registered whereas the violation for fenitrothion is most likely to have resulted from feeding poultry with treated grain. These figures underline the safety of most of the currently registered ectoparasiticides. Presently the National Residue Survey does not test for amitraz, promacyl or rotenone which are also used in ectoparasite treatments. Testing for synthetic pyrethroid residues has commenced recently, It should be noted that the United States has no MRLs in meat for some organophosphates which are used as ectoparasiticides in Australia, cyromazine, cypermethrin, deltamethrin, promacyl or rotenone. Where levels have not been set an effective MRL of zero is taken. This represents a serious potential threat to meat exports (Pryor 1987). Maximum residue limits have not been developed specifically for pesticide Manufacturers of residues in raw wool, lanolin or other livestock fibres. pharmaceuticals and cosmetics are particularly sensitive to the presence of residues in lanolin although these concerns have been addressed to a large extent by the development of processing techniques to remove pesticides from wool grease and the commercial availability of British Pharmacopoeia specified 'pesticide reduced' and 'pesticide free' lanolin (Reed et al. 1989.) In addition, there is increasing concern in Europe about the presence of pesticides, in particular pyrethroids, in wool scouring effluent (Evans 1988). The possibility of hazards from occupational exposure of shearers and farm workers to pesticides in wool grease has also been noted (Reed et al. 1989). Effective methods of controlling parasites which minimise the levels of residues are necessary to avoid possible future problems. USE OF NON -CHEMICAL METHODS OF CONTROL Physical and cultural controls Physical methods can lasting or permanent under valued and they many cases be because back-up. be effective in controlling parasites and are often long in their effect. However sometimes their usefulness is are often not used to their full potential, This may in of the ready availability of pesticides as a 'quick fix' Mulesing, docking tails to the correct length, crutching, shearing and pizzle dropping are cultural methods used to reduce susceptibility of sheep to flystrike. Many believe that by judicious use of these techniques, breech strike can be controlled in all but the worst seasons, Morley and Johnstone (1984) conclude from a review of the development and use of the Mules operation that levels of adoption of mulesing are well below optimum, particularly in non-Merino breeds, despite abundant evidence of the benefkt of the operation to these breeds. Similarly, though the importance of docking tails?0 a mediumlong length to prevent wool staining and subsequent flystrike has been recognised since the work of Gill and Graham (1939), surveys summarised by Morley and Johnston (1984) suggest that, in some areas, more than 50% of producers dock tails too short. These authors suggest that new extension approaches may be needed to increase adoption of correct tail docking and mulesing procedures. The use of trapping to reduce populations of livestock pests has been attempted with many species. Bait bins used early in the season as sheep blowflies (Lucilia cuprina) emerge from over wintering, or placed at strategic sites where populations of flies persist, may be effective in reducing strike incidence in pastoral areas (Anderson 1990). However, traps are likely to have little effect once strike waves have begun, or in wetter areas where fly populations are higher, unless used at impractically high densities (Mackerras et al. 1936). Traps for buffalo flies (Haematobia irritans exigua) may be 39 Proc. Aust. Soc. Anim. Prod. Vol. 18 effective in maintaining fly numbers below economic thresholds on dairy cattle which walk through the trap each day (Roberts 1952; Anon. 1986). As the cattle walk through, brushes dislodge the flies which then fly up to a transparent dome where they are killed. Traps have been reported to reduce the levels of worry caused by various species of biting flies attacking cattle in the United States (Wilson 1968; Meifert et al. 1978) although Drummond et al. (1988) conclude that their usefulness as a practical technology is still to be determined. Sticky traps, baits and 'electrocutor' type traps are sometimes used in integrated programmes to control flies in intensive pig and poultry houses and dairies. Careful sanitation and removal of waste from around dairies and areas where animals are housed removes breeding sites for house flies (Musca domestica) and biting flies such as stable flies (Stomoxys calcitrans), thus reducing the need for pesticide treatments. Conditions which allow rapid drying of poultry manure 'are unfavourable for fly of larvae but favcurable for the various predators'and parasites of fly eggs, 'larvae and pupae (Axtell 19.86). Barriers such as screens, plastic strips and airlocks on entry doors can be used to exclude flies in animal housing areas and barriers of dense vegetation have been shown to impede the spread of biting flies (Tabanus nigrovittatus) from salt marsh breeding sites to cattle grazing areas in the U.S.A. (Morgan and Lee 1977). Wilkinson (1964) showed that moving cattle into a paddock which had not been stocked for 4 months in May, when ticks produced few progeny, and subsequently alternating them between paddocks at 4 monthly intervals controlled cattle ticks (Boophilus microplus). Harley and Wilkinson (1971) reported a modification of this technique which used small tick-free disinfection paddocks to house cattle until all ticks had dropped from them; the cattle were then moved to the main grazing paddocks before they were reinfested by the progeny of the dropped ticks. Both of these methods reduce the need for chemical treatment but, as appears to be the case with most physical and cultural methods, are not used to their full potential (Elder et al. 1980, 1985). Biological control Two categories of biological control can be distinguished, classical or innoculative biocontrol in which an introduced biological agent is expected to persist in the ecosystem keeping the target pest at low levels,and innundative biocontrol where very large numbers of the agent are applied as a 'biological pesticide', Innoculative control programmes, once established, are cheap and reasonably permanent, They do not result in eradication of a pest but may reduce it to below economic levels, either through their own effect or as a part of an integrated programme. However, the possibilities for using innoculative bio-control against ectoparasites with no off-host phase are limited as the control agent must either be very closely associated with the target, such as with a vertically transmitted micro-organism, or must have very sophisticated host locating mechanisms. Those parasites with an off-host phase, such as dung breeding Diptera, are more likely to be amenable to innoculative biocontrol. The most wide ranging biological control programme undertaken in Australia for the control of livestock pests is the introduction of dung breeding insects and mites to control buffalo and bush flies (Bornemissza 1976). The project was initially undertaken following the partial success of a similar project to control horn flies (Haema tobia irri tans irritans), which are closely related to h%f falo flies, in Hawaii. Fifteen species of beetle and a mite, which-attacks the immature stages of the buffalo fly, are now established in northern Australia, and seven species are established in south-western Australia. Dun,g dispersal by the beetles has reached high levels in some areas, and buffalo fly numbers are significantly reduced at times of the year when beetle activity is 40 Proc. Aust. Soc, Anim. Prod. Vol. 18 high (Anon. 1986). Hughes and Morton (1985) failed to detect any significant difference in the number of bush flies over wintering in southern Queensland before and after the introduction of dung beetles. However, Ridsdill-Smith and Mathieson (1988) noted an 88% reduction in bush fly numbers in January following the introduction of summer active dung beetles into south-western Australia. Programmes to introduce spring active dung beetles to prevent early season build-up of bush fly numbers are underway (Ridsdill-Smith pers. corn.), Biological control is an important component of integrated programmes to control flies in poultry houses. Hymenopterous pupal parasites, predaceous beetles, mites and entomophilic nematodes which attack fly eggs, larvae and pupae have been identified. In most programmes in Australia bio-control is achieved simply by the adoption of manure management programmes which allow sites for naturally occurring predators and parasites to carry over, Release of parasitoids to augment natural populations is used on some North American poultry farms although Axtell (1986) notes that this is not always successful. Entomophilic nematodes, which can be reared in large numbers and can be applied to manure as a spray, have been used to control flies breeding in poultry manure with some success in Canada (Belton et al. 19871, but results have been less favourable in other environments (Geden et al. 1986). In the early 19008, at which time it was believed that the majority of L. cuprina bred in animal carcasses, a number of parasites and predators including a pupal parasite (Nasonia vitripennis) a larval parasite (Alysia manduca tor) As the and a number of predaceous beetles were introduced (Anon. 1933). majority of L. cuprina breed on live animals and few emerge from carcasses (Waterhouse 1947), these methods were doomed to failure. The use of Bacillus thuringiensis, a bacterium which has been successfully used to control a range of agricultural pests, is presently being investigated for the control of sheep blowflies and lice. Initially the aim is to use it as an innundative biocontrol agent, but in the longer term it is hoped to incorporate the plasmid, which codes for the toxic principal in Bacillus thuringiensis, into bacteria which grow in the fleece during fly risk periods (Pinnock 1988). In addition, the potential of an introduced protozoan pathogen Octosporea muscaedamestiae, for reducing blowfly numbers is under investigation (Cooper et al. 1985). An entomophilic nematode, Heterotylenchus autumnalis, was released in California to reduce populations of the face fly (Musca autumnalis) (Anon 1969). A similar nematode parasitizes bush flies in Australia, but does not seem to exert a major regulating effect on bush fly numbers (Nicholas and Hughes 1970). Wharton and Norris (1980) note that B. microplus is predated by birds, scavenging rodents, poultry and ants, but conclude that the potential for innoculative bio-control is poor. Various pathogens ranging from entomophilic nematodes to fungi, bacteria and viruses have been investigated overseas for the control of mosquitoes, black flies and biting midges which can cause losses amongst livestock and can transmit diseases (Lacey and Undeen 1986; Molloy 1981; Platzer 1981). These have been at best partially successful but may assist control when used in integrated programmes. Breeding livestock for resistance to parasites Variation in resistance or tolerance to ectoparasites both amongst breeds and amongst individuals within breeds has been recognised for many livestock species. Sometimes this has a physical basis. For example sheep with wrinkly breeches are mere susceptible to breech strike (Seddon and Belschner 1937) and catt-le with darker coloured coats have been observed to be more attractive to various species of blood feeding flies (Taschiro and Schwardt 1953; Holroyd et al. 1984). Often there also appears to be an immunological basis. The most spectacular use of between breed variation to reduce problems caused 41 Proc, Au&. Soc. Anim. Prod. Vol; 18 by ectoparasites in Australia is the use of BOB indicus cattle in crosses with B. tauruls to increase resistance to B. microplus (Utech et al. 1978). In southeastern Queensland, B. taurus cattle require six spray treatments at 21 day intervals or four pour-on treatments at 35 day intervals commencing in spring whereas B. indicus breeds need only one pour-on or two dip or spray treatments in autumn when their natural resistance begins to wane (Kearnan 1988). Genetic gains in resistance can also be made by selecting the more resistant bulls and cows within herds (Hewetson 1972). In south-eastern Queensland from 1977-78 to 1982 the proportion of producers running pure or crossbred B. indicus cattle increased from 47.8% to 60% (Elder et al. 1985). However, there was no difference in the number of ticks tolerated before animals were treated between owners of B. taurus and B. indicus cattle. Thus in many instances increased use of B. indicus cattle was not translated to reduced chemical treatment. There are well documented variations between strains of Merino in resistance to fleece rot and bodystrike (McGuirk et al. 1978) and estimates of the heritability of liability to fleece rot suggest that genetic gains will be made from selecting within strains (McGuirk and Atkins 1984; James et al. 1987). Sandeman et al. (1986) present evidence which suggests that the type and extent of immune response to L, cuprina larvae is genetically determined. Nelson et al. (1970) divided cattle into three groups on the basis of their response to infestation by the shortnosed sucking louse (Haematopinue eurysternus) : (a) susceptible animals carrying high louse burdens which increased to a point where acute anaemia developed and action had to be taken to save the lives of cattle; (b) carriers that had chronic infestations year round but seemed to suffer no ill effects and (c) resistant animals with few lice despite being housed with louse-infested cattle. Nelson and Baron (1982) suggest that breeding may be a suitable method for improving resistance to sucking lice on livestock and to the sheep ked (Melophagus ovinus). Hall and Goss (1975) present evidence of genetic variation between strains of cockerels in susceptibility to northern fowl mite (ornithonysus sylvarium). Treatment with insecticide masks expression of natural variation in susceptibility and reduces the opportunity for selection of the more resistant animals. This was well demonstrated in Zimbabwe where, prior to independence, a very intensive programme for tick control in cattle operated. This allowed development ,of tick susceptible strains of cattle and when the programme ceased, it resulted in widespread tick infestation and endemic disease (Allen 1979). It is seldom that absolute resistance or tolerance to ectoparasites would result from selection. However, increased resistance delays the time until economic thresholds for treatment are reached, thereby reducing the number of chemical applications required. Immunization Vaccination to protect against ectoparasites is presently the subject of intensive research world wide, Vaccination of cattle with a crude extract of partially fed adult cattle ticks reduced the number of ticks developing on cattle by in excess of 90% in some studies and reduced the size and egg producing potential of ticks that did complete feeding (Johnston et al. 1986). Vaccination stimulates a different immunological response to that induced by natural tick infestation and so does not simply substitute for naturally acquired immunity (Kemp et al. 1986). Field trials to test a recombinant vaccine are presently underway in Queensland (K. Bremner pers. corn.). O'Donnell et al. (1981) demonstrated that circulating antibodies were produced in response to administration of an extract of ground up L. cuprina larvae, but no protection was conferred against larval implants. Sandeman et al. (1986) showed that resistance was induced in approximately half of a group of sheep 42 Proc, Aust. Soc. Anim. Prod- Vol. 18 exposed to four or more consecutive infections with L. cuprina larvae. Possible mechanisms for this resistance are discussed by Bowles et al. (1987). Whereas these researchers are investigating the secretory and excretory products of L, cuprina larvae for antigens that could form the basis for a vaccine, CSIRO Division of Tropical Animal Science is using a 'concealed antigen' approach. This approach aims to find an antigen in the blowfly larvae to which the sheep is not normally exposed, similar to the antigens in the guts of ticks which are the basis for the cattle tick vaccine. Similar methods are being utilised towards developing a vaccine for buffalo fly (K. Bremner pers. corn.). Burrell (1985, 1989) showed that immunisation with an experimental Pseudomonas aeruginosa vaccine prevented exudative fleece rot and subsequent flystrike. Field trials are continuing to test whether vaccination can protect against the range of serotypes and species of bacteria which can predispose sheep to bodystrike in the field. Nelson and Baron (1982) conclude from studies with sheep ked and sucking lice that resistance is locally mediated in the skin and that circulating antibodies to parasite secretions, though often present, are of little importance. Acquired resistance appears to be locally mediated and operates by causing constriction of the blood vessels on which the keds are feeding. As it appears that non-immune systems are most important in the development of acquired resistance to keds, these authors suggest that genetic selection of livestock for resistance may be a more feasible non-chemical approach to control than immunization. However the concealed antigen approach to developing a vaccine may also be a worthwhile avenue for research with these species (K, Bremner pers. corn.). Genetic control of insect populations Genetic control, or manipulation of a pest's genome for its own destruction, has been investigated for use against a number of species of livestock pests since the unparalleled success of the sterile male technique in eradicating the new world screw worm (Cochliomyia hominivorax), a major pest of livestock industries, from Curacao, the Virgin Islands, Puerto Rico and the U.S.A. (Graham and Hourrigan 1977). The sterile male technique consists of flooding the wild population with successive releases of sterilized male flies until the chance of a fertile female locating and mating with a fertile male is effectively reduced to zero. The technique would be economically impractical for use in the eradication of most livestock pests in Australia because of the large areas involved, although it could be useful for regional suppression in some instances. In an attempt to overcome this problem the CSIRO Division of Entomology have developed a number of strains of genetically altered sheep blowflies which transmit genetiq defects to succeeding generations (Whitten et al. 1977). The most successful strains have been the FKS or 'field *emale killing system' strains, The males of these strains are semi sterile when mated to normal sheep blowflies and transmit a number of mutations that result in blindness of females in subsequent generations, The blind females fail to survive to reproductive age while the male progeny continue to mate with normal females and spread the genetic defect. In a trial on Flinders Island in South Australia, release of the FKS strains reduced sheep blowflies to negligible levels at the end of the 1985/86 season and fly numbers increased only slowly again the next year. Further trials are presently underway on Flinders Island in Bass Strait. Results of computer simulation studies suggest that it will be possible to eradicate sheep blowfly from Tasmania and other physically bounded areas using this system but that on the mainland a strategy of ongoing releases aimed at suppression in selected high risk areas may be a more cost-effective approach (Foster et al. 1988). 43 Proc. Aust. Soc. Anim. Prod. Vol. 18 Eradication quarantine and legislative control Eradication of a pest is the most permanent method of control if it is supported by effective quarantine procedures. A number of instances of successful eradication of livestock pests using the sterile male technique have already been cited and others are reviewed by Graham and Hourrigan (1977). The most successful instance in Australia is eradication of the sheep scab mite (Psoroptes ovis) prior to 1896 (Seddon 1964). A programme which aims to eradicate sheep lice (Damalinia ovis) is currently underway in Western Australia (Wilkinson 1986). Eradication of sheep lice would eliminate the major reason for application of ectoparasiticides to sheep in Australia (Reed et al. 1989). Tick-free areas are maintained in both Queensland and New South Wales and strict legislative requirements are enforced for the movement of cattle into these areas. Movement of animals into tick-free areas, whether for sale or slaughter, requires a number of pesticide treatments at short intervals, and there have been instances of pesticide residues resulting from this practice. Reid (1987) recommends that the chance of residues occurring can be minimized by using low risk chemicals such as synthetic pyrethroids at the maximum interval of 7 days before clearance. Although regulatory control and eradication programmes may depend on intensive use of pesticides, in the longer term they significantly reduce insecticide usage. Quarantine requirements are often imposed following eradication, not only to prevent the re-introduction of the pest but also the introduction of other pests. The importance of quarantine procedures to containing costs of production and maintaining markets, but also to reducing pesticide usage, cannot be overstated. For example, the invasion of the screw worm fly (Chrysomyia bezziana) or re-introduction of sheep scab would wreak havoc with Australia's livestock industries and significantly increase the use of pesticides. At the peak of reliance on the use of pesticides for pest control, treatments were applied at the first sign of a pest, when conditions were suitable for a pest outbreak, or sometimes preventatively on a calendar basis at regular intervals, regardless of the presence of pests. Pesticides are now generally used more strategically. Applications may be timed when levels of an infestation exceed an economic threshold, when it is predicted from a knowledge of'the pests population dynamics that economic thresholds will be exceeded if treatment is not conducted, or at a strategic time in the life cycle of the pest to gain a lasting effect. Treatments must also, as far as possible, be planned to minimise residue levels at the time of sale. Application with regard to economic thresholds Little formal work based on cost benefit analysis has been carried out to establish economic thresholds for livestock pests. However, Sutherst et al. (1983) calculated economic thresholds for the treatment of B- microplus for a range of tick damage coefficients, beef prices and treatment costs. An economic threshold of 79 ticks per side was calculated for B. indicus x B. taurus steers assuming product values current at that time, Haufe (1981) noted two different biological responses to horn flies that affected productivity of cattle, one at 12 and one at 230 flies per animal, Between 12 and 230 flies per animal, growth rate was depressed by a relatively constant 17% to 20%, while numbers above 230 depressed growth rate by up to 45%. He concluded that it was necessary to virtually eliminate an infestation to prevent the 17-20% loss in potential growth rate. Results of studies of the 44 Proc. Aust. Soc. Anim. Prod. Vol. 18 effect of buffalo fly on weight gain have been less conclusive. However, Reid (1989) recommends that buffalo fly treatments should be applied when the number of flies exceeds 200 per side on beef cattle and 100 per side on dairy cattle. Arends and Robertson (1986) describe a monitoring system for flies in poultry houses using white cards. Chemical control is commenced when the number of spots per card per week exceeds 50. However, the authors' point out that this ie an arbitrary figure and that thresholds should be established based on the individual farm's needs. It appears that in many instances Damalinia bovis and Linognathus vituli, the major species of cattle lice in Australia, cause little production loss (Arundel and Sutherland 1988). Treatment may be warranted to prevent damage to hides and fences and other fixtures which can result from cattle rubbing. H. eurysternus can have more severe effects and may even cause anaemia and death (Nelson et al. 1970). However, Scharff (1962) found that the proportion of cattle severely affected was less than 2% and that treatment was seldom justified in more than 5%. It may be prudent to cull highly susceptible animals which are a continuing source of infection to avoid having to continually retreat with insecticides. In most instances itchmite in sheep (Psorergates ovis) cause little production lose. Normally special treatments for itchmite will not be warranted (Johnson pers. corn.). Where itchmite become a problem, treatment will be beet timed to coincide with treatment for other parasites, for example a drench of ivermectin for internal parasite control, or when dipping post shearing for louse control. Johnson et al. (1989) indicate that better control is obtained when this treatment is carried out in spring rather than in autumn. Though current estimates suggest that between 20% and 30% of the nation's flocks are infested, treatment for sheep lice is conducted routinely after shearing by approximately 85% of wool growers (Anon. 1988). Approximately 180 million chemical treatments are applied for louse control each year (Reed et al. 1989). This seems to be an inefficient exercise involving considerable unnecessary use of pesticides. Routine treatment of all sheep post-shearing has been necessary in the past for 3 main reasons: 1. 2, 3. Until recently there was no registered method of controlling mid-season infestations other than shearing and treating. It is extremely difficult to detect very light infestations and thus to determine which sheep are infected and which are not. Post-shearing treatment for lice has been a legal requirement in most States of Australia until comparatively recently. The availability of products for long wool l