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 Follow this and additional works at: https://researchlibrary.agric.wa.gov.au/journal_agriculture3 Part of the Biosecurity Commons 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.