Journal of the Department of Agriculture, Western Australia, Series 3

Volume 1 Number 6 November-December, 1952 Article 18

11-1952

The insect vector in relation to myxomatosis

J A. Button Department of Agriculture

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Recommended Citation Button, J A. (1952) "The insect vector in relation to myxomatosis," Journal of the Department of Agriculture, Western Australia, Series 3: Vol. 1 : No. 6 , Article 18. Available at: https://researchlibrary.agric.wa.gov.au/journal_agriculture3/vol1/iss6/18

This article is brought to you for free and open access by Research Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 3 by an authorized administrator of Research Library. For more information, please contact [email protected]. THE INSECT VECTOR IN RELATION TO MYXOMATOSIS IN AUSTRALIA

By J. A. BUTTON, B.Sc. (Agric), Entomologist.

HE rabbit is undoubtedly the greatest single pest with which agriculturalists T in this country have to contend. It is, therefore, not surprising that any new and promising method of controlling the pest should be greeted with considerable interest. Although a great deal has air eady been written regarding the myxo- matosis virus a brief and co-ordinated summary of the situation as it now exists in Australia, with particular reference to this State, should prove of value as a guide to the wider establishment of the disease next summer.

EARLY HISTORY OF THE VIRUS and covered an area of about 400 square Myxomatosis first appeared in Euro­ yards. Two natural warrens were estab­ pean rabbits in South America in 1897 lished within the enclosure. The re­ and eventually reached California, sults obtained were most encouraging U.S.A. in 1930. The virus was brought and conclusively established the effect­ to Australia about this time for re­ iveness of the disease in a confined search purposes. (Anon a, 1951.) space. Enclosure Trials: The initial work in Of more than 600 rabbits which con­ this country was concerned with ensur­ tracted myxomatosis during the course ing that its release among the rabbit of the trial only two recovered from the population would not be followed by disease. spread to man, domestic animals or Field Experiments: The first field native fauna. (Bull and Mules, 1944.) scale trials in Australia were com­ As a result of this extensive research menced late in 1937 on Wardang Island the non-susceptibility of other native and later at Pt. Pearce. The enclosures and domestic animals was conclusively in both cases covered an area of established. Furthermore, the disease approximately 90 acres. The results of was found to be refractory to all rabbit the trials at Wardang Island failed to species other than the European (to show that extermination by means of which the Australian rabbit belongs). the epizootic was possible even though Subsequently experiments in the a considerable population reduction was Eastern States demonstrated the rela­ achieved. Conditions on the island tive effectiveness of the disease as a were, however, dry and unfavourable to method of rabbit control under various mosquitoes. Furthermore, no stickfast conditions. The first of these took the fleas were present. Greater success was form of enclosure or colony experi­ achieved at Pt. Pearce. Here most rab­ ments conducted with wild rabbits. bits were infested with stickfast fleas. These early trials extended over a The importance of the insect vector period of about two years from early in was clearly illustrated by the exterm­ 1937 to late in 1938. Conditions of the ination of all but 17 of a total popula­ trial were far removed from natural tion of about 500 in 60 days. field conditions. The enclosure was The first unenclosed field trial with completely netted on the sides and top myxomatosis under natural conditions in order to exclude predatory animals, in Australia was subsequently arranged 819 Journal of agriculture Vol. 1 1952 late in 1942 at Mt. Victor, S.A. (3,125 genus Aedes appear to be involved. acres). Unlike the previous trial, These comprise A. vittiger, A. campto- migration of the rabbits was permitted rhynchus, A. alboannulatus, A. theo- under natural conditions thus increas­ baldi and A. sagax, the last two men­ ing observational difficulties. However, tioned being the most prevalent. Others no reduction in the total population of which appeared to be important, the trial area was observed. especially late in the season, were Culex More promising results came from annulirostris and Anopheles annulipes. trials commenced at Melton late in Another Aedes species, A. camptorhyn- 1942. An encouraging kill of over 80 chus (common in south-western Aus­ per cent, was achieved in 32-34 days in tralia), appears to offer promise as a one case. Examination revealed that most useful vector (Anon, 1951). stickfast fleas (Echidnophaga myrme- Stickfast Fleas: It has been demon­ cobii) were present in large numbers strated by Dr. L. B. Bull, of the on the rabbits throughout the experi­ C.S.I.R.O., that Echidnophaga myrme- mental area. No significant spread cobii can act as a vector in myxomatosis from the area was obtained. and, as will be seen subsequently, the The overall picture obtained from the probable importance of Echidnophaga results of these early field trials was not spp. in Western Australia as an agent an optimistic one. There was no indi­ of transmission may be considerable. cation that a spread from warren to warren was possible under natural con­ ditions. However, as a consequence of more recent field investigations (commenced April, 1950) by the Wildlife Section of the C.S.I.R.O., myxomatosis has become established widely in river valleys in New South Wales and the Murray Valley in Victoria and South Australia. It is apparent that the infective agent has been spread by insect vectors, pri­ marily certain mosquito species. Very satisfactory results have been achieved over wide areas along the Stickfast Flea (enlarged). main watercourses and also in the [After Monnlg.] larger irrigation districts. Thus good spreads have resulted along many parts Simulium and Sandflies: It seems ap­ of the Murrumbidgee, Lachlan, Darling, parent that any blood-sucking insect Bogan, Macquarie and Castlereagh whose habits favour its repeated feed­ Rivers in addition to the Murray River. ing on rabbits could behave as a vector in myxomatosis. To be of any signifi­ cance in an epizootic, however, VECTOR CONSIDERATIONS reasonable abundance and a degree of Knowledge obtained by observation in persistance of the species would be the Eastern States definitely indicates required. the importance of insect transmission A species of Simulium (sometimes in the recent myxomatosis epidemics. referred to as sandflies) has been ob­ Furthermore, evidence suggests that served feeding on the ears of rabbits on although other blood-sucking insects the banks of the Murray. It would may have been concerned the chief appear that these flies could transmit vectors are undoubtedly certain mos­ the disease but the importance of their quito species. Various species of the role is uncertain.

Journal of agriculture Vol. 1 1952 True sandflies (Ceratopogonidae) re­ At the time the investigation was main still to be established as a signi­ begun the season was well advanced ficant vector in transmitting the disease and many cool nights were encount­ (Anon, 1951). ered, thus rendering it extremely diffi­ cult to arrive at very definite conclu­ MYXOMATOSIS IN WESTERN sions. AUSTRALIA Nevertheless, despite the difficulties The initial work done in Western encountered the following summary has Australia (Jenkins, 1944) was in the been prepared in the hope that it will nature of a stickfast flea survey under­ prove of some interest and perhaps taken with the object of determining serve in some measure as a guide to whether fleas were sufficiently wide­ future efforts aimed at establishing the spread to serve as vectors of the rabbit disease. It is also hoped that the fol­ virus. This work showed the stickfast lowing will emphasise the difficulties flea (E. myrmecobii) to be widely (imposed by climatic and other factors) established among rabbits in various which are likely to be encountered in parts of the State, with the exception this State. of the more southern regions. The first sample of the myxomatosis Northampton virus was obtained in Western Australia This locality was surveyed in mid- in March, 1951, and was immediately March. Myxomatosis was established injected into laboratory rabbits. over a li mile front on the Bowes River Although it was recognised to be too where a 90 per cent, kill had been late in the season to hope that any de­ achieved, and the first evidence of the gree of natural spread of the disease disease in the Nokenena Creek area was would be achieved at this stage, it was becoming apparent. considered that useful experience and All confirmed reports of the disease knowledge could be gained by carrying in this area can be accounted for on out limited trials. the basis of the existing mosquito Sites at Muresk and Bejoording were population. Stickfast fleas (E. gallina- accordingly selected as suitable for ob­ cea) were, however, present in large servational purposes. Both were con­ numbers. sidered to have fairly high mosquito and rabbit populations. The trials were Geraldton Region primarily aimed at providing experience The north-western margins of the in swabbing and injection techniques. Glengarry estate were found to be prac­ At the commencement of the last tically waterless but some isolated season, however (commencing in Aug­ soaks with a few mosquito larvae pres­ ust, 1951) infection centres were estab­ ent were observed. The area extending lished in various parts of the State. over several square miles had, six Selected sites were those considered to months previously, carried a very dense provide the most favourable conditions rabbit population. No evidence of rab­ for the satisfactory development of the bit life could now be found and the disease. disease was estimated to have been at Commencing in March, 1952, a series least 98 per cent, effective. Local re­ of surveys was made in the areas in ports maintained that the mosquito question with the view to throwing population of the area had been insig­ more light on the insect transmission nificant but that stickfast fleas had mechanism operating. In cases where been dense. the disease had failed to give satis­ It seems unlikely that mosquitoes factory results it was hoped that the could have been the most important investigation would disclose some ex­ vector in the spread of the epizootic in planation for the failure. an area such as this.

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Journal of agriculture Vol. 1 1952 The original depot of the Greenough upper reaches of the river, but in the River area had been situated on the south it had achieved an excellent river at "Glengarry". At the time of control and was at a standstill. Mos­ this survey it was claimed that a con­ quito larvae were found at various trol of 98 per cent, or more had been places along the river, indicating a fair achieved. It was also claimed that the population of mosquitoes distributed mosquito density had been negligible over this area. At one locality mos­ during the flare which commenced as quitoes were trapped coming from early as September and reached its most of the rabbit burrows along a height during December and January. half-mile front. The mosquitoes were It was suggested that the sand-fly had found to be all the one species (A. been largely responsible for the early annulipes). Subsequently this species flare and that the flea population, was also observed in similar circum­ which became dense during December stances at a locality some eight miles and January, continued to spread. The distant from the above. mosquito, it was said, was insignificant until the end of January. Claims such Broadly speaking, most of the affect­ as these, however, obviously need to be ed areas in the East Chapman region investigated. were in close proximity to the river or similar water supply. Fleas were re­ A report of some interest came from ported to be present in the area but, this area and is worth recording. It is nevertheless, the mosquito population asserted that when the disease was quite sufficient to account for the actually flared at "Glengarry" it was disease spread over most of this region. confined within a rabbit-proof fence From the entomological viewpoint which divided the river flats from the the method of artificial spread employ­ outer margins. The disease spread ed throughout these areas is of some rapidly along the river but could not be significance. The vermin inspector induced to start outside the fence. responsible concluded, after repeated Finally the rabbit-proof gates were failures to start the disease, that the opened and within a week a spread cage method of spread recommended outside was achieved. by the C.S.I.R.O. was unsatisfactory for This report is of interest because, on local conditions. He found, and has it the surface, it appears to strengthen seems demonstrated, that the most the case for the stickfast flea as an effective technique of bringing about an important vector in this region. initial flare is to release numbers of in­ The so-called drier region to the fected rabbits at intervals along the north between "Glengarry" and the course of the selected stream. The Mullewa Road was the site of a very adoption of this technique it is claimed extensive spread of myxomatosis which led to a most satisfactory result where was still progressing. Most of the area the previous method had failed. This was some miles from any watercourse: again, if its authenticity can be estab­ however, numerous soaks were observed lished, also tends to add weight to the in the gullies. Examination revealed theory of the flea as an important that some contained mosquito larvae, vector. but it did appear that the spread of the disease was such as to suggest that Bejoording some vector other than the mosquito was also significant. At the time of the survey the opening rains had already occurred. In con­ The last distinct site of the disease sequence many of the smaller brooks examined was an area which stretched and streams had commenced to flow for about ten miles along the margins and this could be expected to have had of the East Chapman River. The dis­ an adverse effect on the mosquito lar­ ease . was still progressing towards the vae population.

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Journal of agriculture Vol. 1 1952 The survey was commenced at chief operating factor in the spread "Glendearg" the property of Mr. Lude- achieved. man. In isolated pockets the disease Other reported outbreaks were in­ was found to be still active but over vestigated but no significant facts most of the property a Grade I condi­ emerged nor could the reports be con­ tion had been established. firmed. The creek along the northern margin of this property was inspected and no Bolgart mosquitoes or larvae could be found. The creek banks showed evidence of A reported outbreak at Bolgart on the previously harbouring a moderately property of Mr. Manuel was investi­ dense rabbit population, although in­ gated. Here infected rabbits had been dications suggested only very slight obtained from Bejoording, penned and present activity. Although no mos­ released after seven weeks. The pens quitoes could be found, mosquito-like had been located between two salt Chironomids were observed in the bur­ channels of the Bolgart Brook. The rows. These are not blood-suckers and first evidence of spread was seen about could not therefore behave as vectors. a week after closing the pens and at the time of our examination had been Probably the most significant ob­ working for about one month. In some servation made on this property was places good Grade I proportions had that the rabbit population appeared been achieved. A spread about two never to have been particularly dense miles up both the Bolgart and Yulgan (as compared, for example, with the Brook and downstream about one mile Geraldton area). This fact may well from the site of the pens had been have been the most important factor obtained. Larval specimens were ob­ in the relatively poor progress of the tained from the pools and a high mos­ disease throughout this area. quito population was reported. An The disease was found to have spread absence of stickfast fleas was main­ successfully over a property owned by tained. Mr. Blakeston to the •west of "Glen­ The most significant feature of the dearg". The owner claimed that spread in this area would appear to be abundant mosquitoes were present in the way in which the disease is con­ the vicinity of soaks on his property fined to the creek margins; the mos­ but that no stickfast fleas had been quito population is high along the observed to be present on rabbits ex­ creeks; there is an apparent absence of amined for them. fleas in the drier adjacent areas and An examination of the One Man Road the disease has made no progress what­ locality some miles south of Bejoording ever in these parts. Siding revealed no evidence of the disease further than about one mile south of the centre. A. healthy rabbit Muresk was shot and examined in this locality; Results achieved at Muresk have only one flea identified as E. gallinacea been very disappointing. Odd infected could be found. rabbits have been found on various Over most of the Bejoording townsite parts of the property for a considerable area a Grade I condition had been ob­ period but no worthwhile flare has been tained. This area adjoined and was obtained. The failure at Muresk is continuous with "Glendearg". The difficult to explain. Mosquitoes have affected area, then, in the vicinity of been prevalent for some months and it the centre was no more than two miles may be that the rabbit population itself square. is insufficient to bring about a real flare, Despite conflicting reports it seems or that results have been obscured by clear that the mosquito vector was the inwardly migrating rabbits.

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Journal of agriculture Vol. 1 1952 Beverley measure of control. In these places the At Beverley the myxomatosis centre control has been as high as 90 per cent. was situated on the Dale River at the However, this has been offset to a con­ property of Mr. Norris who was respon­ siderable extent by the invasion of sible for the pens. Mr. Norris was migrating rabbits from neighbouring contacted on April 8 and he was able unaffected areas. A feature of these to furnish much valuable information. few successful outbreaks is the appar­ From this and information gathered ent inability of the disease to progress from extensive operations made over naturally for any significant distance the course of two days, it was possible to localities. Only on two or three pro- complete a general overall picture of from the infection pens even though the progress of the disease in the area. the watercourses on which these were situated provided apparently ideal con­ The disease was confined to the mar­ ditions. gins of the Dale River and there was no real spread further than two miles COMMENTS from the river. The affected areas The differing results in various loc­ along the river were in the main river alities suggest significant environ­ flats bounded by either rocky hills or mental dissimilarities. This, however, sand plain heath, both of which pro­ was not the case. Where the disease vided excellent natural breeding was apparently being maintained in grounds for rabbits. The most striking only a smouldering state environmental feature of the disease in this region was conditions did not appear to differ the continual reinfestation of dead markedly from those prevailing where warrens on the river banks, as a result the results had been more satisfactory. of rabbit migration from the surround­ In both cases pens were located in fav­ ing breeding grounds which had been ourable positions adjacent to creek or little affected by the disease. river pools and mosquito activity had apparently been quite high. Further­ Mr. Norris has observed the disease more, stickfast fleas were generally clean out one particular warren five prevalent in most areas. times after reinhabitation by migrating rabbits. Clearly, then, the "smouldering" The stickfast flea would seem to have condition is not easily accounted for, been not as prevalent as in previous but it is possible that the results of years and in some parts had been the disease, in certain localities at entirely absent. It is possible that this least, were partly obscured by rapid re- factor may have been partly responsible infestation of migrating rabbits in the vicinity. for the poor progress made away from the river. It seems possible that more suitable However, on the river about 15 miles weather conditions may occur in future south of the centre fleas were reported seasons. The two inches of rain which to have been present in large numbers fell in the district in December by dis­ on the rabbits all the season. Further­ turbing the stagnant condition of the pools, may temporarily have had an more, mosquitoes were numerous. How­ adverse effect on the mosquito popula­ ever, despite satisfactory vector con­ tion. ditions no spread of the disease had been obtained. Even so indications suggest that be­ cause of the coolness of the nights, and Gnowangerup perhaps other limiting factors operat­ The survey of this area revealed dis­ ing in this part of the State, more appointing results. The disease is per­ difficulty may be encountered in mak­ sisting in a smouldering condition in ing use of myxomatosis as a means of numerous isolated and very confined rabbit control. The potential value of perties had the disease achieved a the disease would appear, nevertheless,

Journal of agriculture Vol. 1 1952 to be high. It is clear in a district revealed in this survey, is of interest. A such as this that a factor of the utmost number of previous records have been importance is the co-operation of every reported but several of these have sub­ farmer. No worthwhile results can be sequently been shown to be based upon obtained if the efforts are isolated and erroneous identifications (Seddon, the pens widely separated. It is neces­ 1951). The Western Australian speci­ sary for each individual farmer to co­ mens referred to by Seddon were sub­ operate in a concerted and patient mitted for identification to Dr. Jordan attempt to spread the disease. If such of the British Museum. is attempted a considerable degree of control can be expected. Lice of the Family Haematopinidae (probably Haemodipsus ventricosus) SUMMARY have recently been recovered from Generally, results achieved this rabbits at Bridgetown and Manjimup. season have been most encouraging, H. ventricosus has been shown by the especially those obtained from the C.S.I.R.O. to transmit the disease under Greenough area. In many of the other laboratory conditions. districts the main factor limiting suc­ There is an apparent need for further cess would appear to be apathy on the study of the vector factor in myxo­ part of the local farmers matosis in this State. A greater under­ In most regions the mosquito appears standing of this aspect of the disease to be the chief agent responsible for is important in order that the poten­ the spread of the disease, the most tial application and value of the epi­ prevalent species being A. camptorhyn- zootic in Western Australia can be chus, A. alboannulatus, C. fatigans and more accurately assessed. A. annulipes. The stickfast flea ap­ pears to have played a significant role in parts of the Greenough area and ACKNOWLEDGMENT may in subsequent seasons become The author is indebted to Mr. D. J. more important in other parts of the Lee, School of Public Health and State. Tropical Medicine, Sydney, for valuable The prevalence of the poultry "stick- assistance in the identification of mos­ fast" (E. gallinacea) on the rabbits, as quitoes submitted to hm.

RECORD OF BLOOD-SUCKING INSECTS FROM MYXOMATOSIS AREAS (SEPTEMBER, 1951 - AUGUST, 1952)

Spring Summer Autumn Winter Sept -Nov. Dec.-March April-May June-August Aedes alboannulatus 12 1. 6, 7, 10 3, 14, 4, 15 A. camptorhynchus 1. 2, 8, 12 8, 9 6 3 A. aegypti 4 6 A. notoscriptus 10 Culex fatigans 6, 12 1. 3, 6. 7 3, 6 3. 14 C. annulirostris 10, 11 Anopheles annulipes 1, 6, 9. 10 3, 6 3 Echidnophaga myrmecobii 3, 8, 6 6, 8 14 E. gallinacea 1 1, 3, 8 3, 14, 1 Key to Centres: 1. Geraldton 4. Kellerberrin 7. Narrogin 10. Donnybrook 13. Manjimup 2. Moor a 5. Muresk 8. Gnowangerup 11. Coolup 14. Moonijin 3. Bejoording 6. Beverley 9. Bridgetown 12. Kojonup 15. Cunderdin 828

Journal of agriculture Vol. 1 1952 REFERENCES Anon a, Dept. Agric. S. Aust. (1951), Beaurespaire Aragao (1943) — "The Press Bulletin No. 9/51. Virus of Myxomatosis in the Wild Rabbit and its Transmission." Mem. Jenkins, C. F. H. (1944)—"Notes on the Inst. Osw. Cruz. 38. Fasci., pp. 93-99, Distribution in S.W. Australia of Rio de Janeiro. Echidnophaga myrmecobii." Bull, L. B., and Mules, M. W. (1944)— Ratcliffe, F. N., and Fenessy, B. V. "An Investigation of Myxomatosis (1951)—"Mosquito Borne Myxoma­ Cuniculi with Special Reference to tosis." Press Bulletin, C.S.I.R.O. the Possible Use of the Disease to Control Rabbit Populations in Aus­ Seddon, H. R. (1951)—"Diseases of tralia." J. Coun. Sci. Ind. Res. Domestic Animals in Australia," Pt. 2, (Aust.), Vol. 17, No. 2, May, 1944. Service Publication (Division of Vet­ Anon, Com. Sci. Ind. Res. Org. Rabbit erinary Hygiene), No. 6, Common­ Myxomatosis (1951): Progress Re­ wealth of Australia, Dept. of Health, ports Nos. 1-5. p. 154.

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Journal of agriculture Vol. 1 1952