REPORTS AND SUBMISSIONS
- 4.1 Insects
- 4.1.1 The papaya fruit fly (Bactrocera papayae)
- 4.1.2 The incursion of Bemisia tabaci biotype B
- 4.1.3 Western flower thrips (Frankliniella occidentalis)
- 4.1.4 The cucurbit thrips (Thrips palmi)
- 4.1.5 Old world screw-worm fly (Chrysomyia bezziana)
- 4.1.6 Russian wheat aphid (Diuraphris noxia)
- 4.1.7 Honey bees and pollinators
- 4.2 Weeds
- 4.3 Plant pathogens
- 4.4 Human disease organisms
- 4.5 Animal disease organisms
It is likely that Australia receives many new species of plants and animals each year and that, because most of them do not cause immediate and recognised harm to primary industry, they go unremarked. Some indication of the extent of this can be gauged from the experience of the United States where estimates of exotic species have been made (see U.S. Congress, Office of Technology Assessment, Harmful Non-Indigenous Species in the United States,OTA-F-565. Washington 1993).
Estimated number of exotic species in USA
|Insects and arachnids||>2,000|
|Molluscs (non marine)||91|
Many of the species listed in this table are not pests, but the figures demonstrate the overwhelming abundance of arthropods and plants among the exotic species. Some 235 of the exotic insects in USA are regarded as important pests (Schwartz and Klassen, 'Estimate of losses caused by insects and mites to agricultural crops' in CRC Handbook of Pest Management in Agriculture vol 1 pp 155-77. Boca Raton, CRC Press, Florida 1981).
Similarly, in Japan 172 of the 239 exotic insects are pests ( Morimoto and Kiritani, Fauna of exotic insects in Japan, Bulletin of the National Institute of Agroenvironmental Sciences 12: 87-120, 1995).
Unfortunately, comparable figures are not available for Australia, but it is probable that our number of exotic insect pests is similar to that of USA. In the report of the Review of NAQS (Nairn and Muirhead 1995) the arrival in recent times is recorded of 19 insect pests, 1 weed and 7 animal and bee diseases, so that the preponderance of insect intrusions is continuing. Some of these recent incursions are examined in more detail below, in order to provide lessons to be learnt for future preparedness.
Section 4.1 outlines a number of cases where the incursion has involved the entry into Australia of insect species which are likely to have a major adverse impact on sustainable agriculture and the environment. Several of these pests e.g. whitefly and western flower thrips have most likely entered Australia on more than one occasion. Others, e.g. old world screw-worm and Russian wheat aphid have failed to gain entry. Recommendations arising out of these case histories are largely dealt with in Section 3, Routes of Entry, and, to a lesser extent, in Section 5, Key Considerations.
The Oriental fruit fly (Bactrocera dorsalis) is a species complex, the so called 'dorsalis' complex, which has recently been shown to comprise 52 species, of which seven are known to 4 attack cultivated fruits. They are major pests in many areas throughout southeast Asia (their native range) and have invaded islands in the Pacific and parts of North and South America.
Members of this complex have long been recognised to be major potential pests for Australian horticulture; they may 'island hop' into northern Australia, they can travel long distances on small vessels or light aircraft, or arrive as eggs or larvae in infested produce, thereby breaching the quarantine perimeter at more southerly ports in Queensland than Cape York peninsula itself. To confuse the matter there are several native pestiferous fruit flies, which already entail substantial costs in control and the restriction of movement of fruit within Australia and overseas. The most important of the native species is the Queensland fruit fly, Bactrocera tryoni.
In 1974 the mango fly (Bactrocera frauenfeldi), was found on Cape York peninsula. The arrival of this species from PNG resulted in a series of detection traps being established around the coastline from Queensland to Western Australia. In 1975 these traps detected another species, Bactrocera opiliae, on Melville Island off Darwin, which was first identified as the Oriental fruit fly. However, this species, while a member of the 'dorsalis' complex, proved to be a native species, restricted to one native fruit.
The Lindsay Committee, in its Report on aerial littoral surveillance and Northern Australian quarantine strategy (1987) identified the importance of northern Australia, in particular the Torres Strait-Cape York region, as the route of entry for pests and diseases to mainland Australia and noted that, if an exotic pest or disease gained entry by natural means or by human breach of quarantine, it would obviously be important to detect its presence at the earliest practicable opportunity.
The Northern Australia Quarantine Strategy (NAQS), established in 1989, was a direct outcome of this Report and took over management of the previous monitoring system. Survey stations were maintained along the northern coast of the mainland and on several islands in Torres Strait. Surveys to identify pests in Irian Jaya and PNG were commenced in collaboration with local people in Indonesia and Papua New Guinea.
The distribution of thirteen traps on islands in Torres Strait and six sites on Cape York (all within 30 km of the Cape) was based on the assumption that fruit flies would cross Torres Strait moving from island to island (island-hopping) and so arrive at Cape York.
The possibility that the flies could arrive at other locations was considered in a report of the Horticultural Policy Council in April 1991, which stated that 'It is of some concern however, to find that such [efficient detection] systems are not being used at many of the most likely entry points for these species around Australia, the major and minor seaports and airports. Consequently, if an exotic species succeeded in gaining entry at one of these ports and becoming established it is probable that its presence would remain undiscovered for a considerable period, perhaps until eradication had become too difficult or too costly to contemplate.' The Report contained the recommendation that monitoring for fruit flies should be conducted at major and minor ports and airports and it listed Sydney, Newcastle, Brisbane, and Cairns as high risk areas. This report was considered by the Standing Committee on Agriculture in February 1992, but no traps were set out in Cairns.
In November 1991 a report commissioned by the then Bureau of Rural Research on behalf of AQIS also contained a recommendation that trapping should be conducted at ports of entry. No traps were set out in Cairns despite this recommendation.
In early 1992 one of the Oriental fruit fly complex, Bactrocera papayae, was identified at Merauke in Irian Jaya and soon afterwards found in PNG, just over its border with Irian Jaya. In early 1993, the papaya fruitfly was trapped on Boigu and Darnley Islands. Traps were set out on many other islands and flies were trapped on Saibai, Dauan and Stephen Islands. Eradication measures were undertaken on Stephen and Darnley islands in Torres Strait and were judged successful.
In early 1995 this species was again detected on Darnley and Stephen Islands, as well as on Murray and Yorke Islands in Torres Strait. Then in October 1995 came the announcement that the papaya fruit fly had been found on the mainland near Cairns. An intensive survey showed that the fly already occupied a large area centred on Cairns, Mossman to Bingil Bay, along the coast and inland to Mareeba, and was presumed to have been present for up to two years.
The main lesson from the papaya fruitfly incursion is that the recommendations of expert committees should be heeded; it was predicted that fruit flies of the 'dorsalis' group, like the papaya fruit fly, would most likely enter Australia through ports/airports, with Cairns as the most likely port of entry, and yet it seems that this pest was present for up to two years in the Cairns area before detection. The AQIS Bulletin for Nov-Dec 1995 maintains that the Northern Australia Quarantine Strategy could not have done more to detect or eliminate this pest. On the evidence the Academy considers that more could have been done, and that it is important to acknowledge this. Eradication would have been much easier and cheaper if the invasion had been detected soon after it began.
Fruit flies have been eradicated from invaded areas more often than any other group. This is because of their attraction to chemical lures; the largest number of species to methyl eugenol or cue-lure. Traps baited with one of these chemicals attract male flies and can be used as a sensitive and efficient system to detect the flies early in the infestation; the earlier they are detected the easier it is to achieve eradication. In addition, techniques have been developed that are aimed at specific weak links in the defences of the flies: to remove males using the chemical lures; to remove females using hydrolysed protein lures; and to use the Sterile Insect Technique to achieve eradication.
These methods have been well developed and successfully employed in Australia to eradicate the Mediterranean fruit fly from Carnarvon and the Queensland fruit fly from Perth. A joint Federal-State programme is underway to research and develop these techniques to control the Queensland fruit fly in southern Australia, in order to maintain fruit fly area-free status, so that exports can continue with minimum disruption. Infestations of the Queensland fruit fly and the Mediterranean fruit fly have been eradicated many times in southern Australia. Likewise, the true Oriental fruit fly, Bactrocera dorsalis, has been found in California more than a dozen times and each time it has been eradicated
However, because of the delay in detection, eradication of the papaya fruit fly from north Queensland will be a major task. The only comparable campaign is in southern Mexico, which aims to prevent the Mediterranean fruit fly spreading northwards from Central America. This campaign has been successful, but the wider aim of pushing the fly out of Central America is in abeyance.
The situation in north Queensland has advantages over Mexico in that the flies cannot spread into our drier inland. Provided the papaya fruit fly cannot maintain high populations in the rain forest fruits, eradication may be possible.
The silverleaf or poinsettia whitefly, Bemisia tabaci is a serious pest of horticultural crops and cotton and has the potential to cost these industries more than $300 million annually. It can cause damage through feeding, through the transmission of plant viruses, and by fouling produce with honeydew and sooty mould. The B biotype is especially difficult to control as it is resistant to most of the insecticides currently registered in Australia against whiteflies. Furthermore, it has a wide host range, rapid rate of development and produces up to 300 eggs/ female, attributes which together enable populations to increase in size rapidly.
Bemisia tabaci biotype B was first detected in Darwin in October 1994. The chain of events leading to the Northern Territory detection is unclear and probably will never be known. However, on the basis of circumstantial evidence, it is likely that it was introduced sometime between mid-1992 and early 1993, well before its detection in October 1994. At that time, poinsettia cuttings were imported into Australia from the USA by a nursery operator in Coffs Harbour, passing through the normal fumigation with methyl bromide and 3 month quarantine period, without the whitefly being detected. Plants were then propagated and sent to nurseries in New South Wales, Queensland and the Northern Territory. In June 1993 Delta Nursery in Queensland suffered a whitefly infestation, which was uncontrollable with organophosphate and synthetic pyrethroid treatment. The timing of the outbreak in Delta Nursery coincided with the purchase of a shipment of poinsettia from Brindley Bros in Coffs Harbour, the only purchase of poinsettia made that year. They then purchased Encarsia formosa (a parasitic wasp used to control a different species of whitefly) from Biological Services in Loxton. After the release failed to control the infestation they then sent infested material to James Altman of Biological Services in Loxton, who identified the whitefly as Bemisia tabaci. The fact that applications of insecticides failed to control the infestation suggests that the whiteflies were not the native form of Bemisia tabaci (which is easily controlled by these insecticides), but rather was the new B biotype. Also material from a culture set up using whiteflies collected in mid-1993 has subsequently proven to be the B biotype.
Since the original introduction was legal and went through the standard methyl bromide fumigation and 3 month quarantine, we must ask why the methyl bromide fumigation failed, and why was the whitefly not detected during the 3 month quarantine period?
There are several possibilities. Firstly, since there is no evidence that methyl bromide fumigation is ineffective when applied correctly, the failure may have been due to an incorrect, lower dosage being used or to the duration of exposure being shorter than necessary.
Secondly, methyl bromide fumigation may not have been carried out. Several nursery operators involved in the initial introduction have suggested that, because poinsettia cuttings suffer adversely from methyl bromide fumigation, the cuttings were dipped in an insecticide/oil mix rather than being fumigated. If this was so, the insecticide used could have been ineffective against this biotype, or packaging around the cuttings (it is not known whether there was any) may have impeded penetration of the fumigant and so reduced its effectiveness.
Thirdly, biotype B is known to have resistance to the chemical said to have been used. It is known that pest species, like whitefly, can readily evolve resistance to commonly used pesticides, so pesticides, to which the species has long become resistant in its region of origin, cannot be relied on for control in Australia
Dr P. de Barro, author of a dossier (1995) on the whitefly and its implications for Australia (de Barro, Bemisia tabaci biotype B: a review of its biology, distribution and control, CSIRO Division of Entomology, Technical Paper number 33, July 1995), provided some further possibilities why whitefly was not detected during the 3 month quarantine. Some nursery operators consider that post-fumigation quarantine inspection is inadequately performed, citing several examples: on more than one occasion no inspections were carried out over the 3 month period; inspections were so brief that very few plants could have been checked; some quarantine inspectors did not know what to look for because, due to restructuring, several experienced in veterinary-related diseases were transferred to plant quarantine without the necessary training; a single thorough inspection was made very early in the first month but was not followed by a later inspection. The latter is crucial, as the time of the year that the importation is made can directly affect the rate of development of the whitefly. This is temperature-dependent. Since most nurseries do not have heated quarantine glasshouses, a 3 month period at low temperatures would be insufficient to allow development to be completed. It is thus possible for any whiteflies surviving fumigation to pass through quarantine undetected. This problem is compounded by the fact that whitefly eggs and nymphs are minute and, when in low numbers, can easily be overlooked, especially on light coloured foliage. This is of course aggravated if the inspector does not know where on the plant to look for a cryptic species like Bemisia tabaci.
Western Flower Thrips (WFT), originally from south western USA, has become widespread around the world in the past 10 years, largely as a result of the trade in cut flowers (see Section 3.3). First recorded in Australia in 1993, it represents a major threat to plant production in this country because it is exceptionally aggressive and capable of feeding on a wide range of plants. The disease it carries, tomato spotted wilt, has been known in Australia since the 1920's, to be carried by two other introduced thrips species. However, neither of these thrips feeds to any great extent on native Australian plants.
The risk with western flower thrips is that, because it is so invasive, it might introduce the disease to native plants. This would not only increase the available pool of infection for cultivated plants, but could also have serious implications for the native Australian flora. Unfortunately, this thrips seems to exist as a series of biological strains that can only be distinguished biochemically, although they can have very different biological properties. Biochemical work at the Biological Chemical Research Institute, Rydalmere has demonstrated that WFT has been introduced into Australia from at least two sources, and a third strain which lives only on lupins, has been known in New Zealand for many years. WFT currently seems to be undergoing a phase of establishment in Australia, and is not expanding rapidly from the few foci that have been identified. This is not without precedent with immigrant pests, and should not be taken as any form of consolation. Moreover, the existence of different strains of the species suggests that the horticultural trade could easily introduce further strains to this country if quarantine restrictions are not maintained.
The lessons to be learnt from the pest incursion into Australia have been dealt with in Section 3.3.
Thrips palmi (cucurbit thrips) has become abundant throughout the Oriental region only in the past 20 years. Originally described from Sumatra in 1921 this invasive thrips is a serious pest of cucurbits, but also attacks eggplant, potato, tobacco, cotton and many other plants: it has also been implicated as a vector of tomato spotted wilt virus (Houston, K.J., Mound, L.A. and Palmer, J.M. 1991. Journal of the Australian Entomological Society. 30: 231-232). Thrips palmi has spread rapidly throughout the Pacific, including New Caledonia.
The first record of Thrips palmi in Australia was at Darwin, NT, in June 1989, where a serious outbreak was reported in a field of melons at Berrimah, south of Darwin. A monitoring programme revealed that it was established on properties at Berry Springs, Howard Springs and Humpty Doo, and occupied an area approximately 10 kilometres wide and winding 45 kilometres south of Darwin. Later records reported it 20 kilometres further west on the Adelaide River plains, and Katherine, 270 kilometres south of Darwin (Layland, J.K., Upton, M.S. and Brown, H.H. 1994. Journal of the Australian Entomological Society. 33:169-173).
In July 1990 a single severe outbreak was recorded in Queensland, confined to cucumbers in a glasshouse near Ormiston, some 20 kilometres south west of Brisbane. This infestation was believed to have been eradicated. However, in May 1993 a serious outbreak of Thrips palmi was discovered on capsicums at Wellington Point, only a few kilometres to the north of the first infestation. No action to eradicate this outbreak was made, and by 1995, Thrips palmi had been found throughout the surrounding Redlands horticultural district and also to the north of Brisbane in the Caboolture district.
The outbreak in the Northern Territory had serious repercussions for the economy of the Territory, not only due to the damage inflicted on the crops, but also due to quarantine restrictions imposed against the Territory by the States. In 1988 horticultural exports from the Territory were worth close to $7m; by 1992 this had dropped to little more than $2m, and the viability of NT horticulture was at stake. In the initial outbreaks the thrips populations were so high that some crops were either abandoned or ploughed in. Subsequently, properties on which T. palmi was found, during an intensive monitoring program that followed the initial discovery, were prevented from marketing their produce in other States. The fact that the effects of these infestations have declined markedly in subsequent years to the extent that, in 1993, it was claimed that Thrips palmi no longer caused significant losses under Australian managerial practices, should not be any reason for complacency: this might not have occurred, and it may well become a serious pest in any new outbreak area. The possibility of eradication was considered in 1989 but rejected because of the wide range of host plants and the area of distribution at the time of detection.
Considering the rapid and well reported international spread of this thrips in other countries over preceding years, its absence from any AQIS priority list, is incomprehensible. Furthermore, the fact that amaranth, chicory and endive, all of which are known hosts of T. palmi, are allowed to be imported into Australia from countries in which the insect was known to occur, probably accounts for both the NT and Queensland introductions, rather than having arrived on monsoonal winds. A further problem in the Northern Territory stems from the closure by AQIS of its quarantine facility in Darwin, where imported plant material could be safely grown until cleared of any pest or disease. It is now far too costly, and quite impracticable, for NT growers to pay for the use of the full-cost-recovery facilities in southern States, thereby putting pressure on importers to introduce material illegally (see Section 5.4).
The sterile insect strategy for the eradication of old world screw-worm was based on this species' possible entry into Australia from Papua New Guinea (PNG) via Northern Australia, especially Cape York Peninsula. Following the interception of this species on a returning livestock ship in Darwin in the late 1980s, it is now recognised that this pest could enter via any major port in either temperate or northern Australia. Most of this marine traffic originates in the Middle East or Asia, rather than PNG, and consequently the biotype entering Australia could be quite different from PNG strains of screw-worm. This realisation has major implications for early detection strategies and eradication attempts using sterile males.
In the last 15 years severe damage has been caused to the wheat and barley industries of South Africa, the USA and Canada by the appearance in these countries of the Russian Wheat Aphid (RWA), Diuraphis noxia. Before 1935 it was not known outside the Ukraine and central Asia. It spread west in the 1940s into the Mediterranean and thence into Africa in the 50s reaching South Africa in 1978 and North America by 1986.
Australia can expect at some future time to host this major pest of wheat and barley, and its continued absence is a credit to AQIS. This illustrates the value of pre-emptive action. A workshop was convened in 1986 and a set of measures were agreed upon, aimed at placing Australia in the best position to contain RWA on its arrival in Australia and to minimise its economic impact. These included:
- collation of all relevant information on RWA in the published literature and its availability to interested workers.
- CLIMEX predictions of likely distribution and pest status of RWA in each area.
- registration of appropriate pesticides for prompt action on RWA's arrival.
- introduction of natural enemies of RWA on other cereal aphids, ready for transfer to RWA populations .
- isolation from commercial wheat cultivars of genes that provide resistance or tolerance to the toxic effects of RWA.
Australia is now better prepared to cope with RWA if and when it enters Australia. However, there is a danger of this information being lost or becoming less useful in the absence of a 'RWA incursion' contingency plan. This would prevent the loss of 'corporate memory' if the incursion is some years off.
In the case of biological control of RWA, parasites were introduced into Australia, but there is no evidence of their successful establishment on other cereal aphids. However, shipments of these parasites, obtained by CSIRO from the USSR, were sent to South Africa, where they have successfully established on populations of RWA. Studiesin South Africa also suggest why the parasites did not establish on other cereal aphid species in Australia. South Africa currently represents a source of parasites for rapid introduction into Australia if needed. Similarly, genes have been identified in commercial cultivars of Australian wheat, which confer partial resistance or tolerance to RWA in host plants. This work, conducted in CSIRO's Montpellier laboratory in France, demonstrated that all the useful genes were isolated from cultivars whose ancestry could be traced back to the center of origin of the RWA in southern Russia and Afghanistan. Wheat breeders are now better placed to select wheat cultivars known to be tolerant to RWA, although this need has yet to be exploited. A comprehensive synopsis of information on RWA was completed in 1988 and updated in 1996. Much of this research was funded by the precursor of the Grains R and D Corporation.
The pre-emptive work on RWA shows how Australia can be prepared for incursions of major arthropod pests of crop plants. In this regard, Australia is much better prepared for incursions of pests and diseases of livestock than for pests of plant species that are important in horticulture, crops, pastures and forests. The Review Team should address this imbalance in Australia's preparedness to cope with invaders.
The Academy urges the Review Committee to investigate why Australia appears better prepared to cope with certain livestock diseases than with adverse plant health and environmental impacts of incursions of unwanted pests and diseases into Australia. This imbalance appears to have a historical basis and should be redressed as a matter of urgency.
The greatest value of honey bees (Apis mellifera) to Australia is in the work they perform as pollinators of commercial crops and other plants. The economic importance of exotic diseases and pests of Australian honey bees should not be underestimated.
A set of strategies to be used as guides for controlling economically important exotic diseases and pests of Australian honey bees, once they are detected in Australia, are an integral part of the Australian Veterinary Emergency Plan (AusVetPlan, Edition 2.0). These strategies relate to the potential pests of honey bees, Tropilaelaps mite, Varroa mite, Braula fly, and tracheal mite, and to the potential competitors, Asian honey bees and Africanised honey bees. The strategies were approved by the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) and are reviewed regularly. However, these diseases and pests of honey bees are not included in the Commonwealth/States cost-sharing agreement for the eradication of certain exotic animal diseases. The Academy does not understand this omission.
The AusVetPlan technical response plan for bee diseases details biological and pathological aspects of each exotic disease and pest, outlines principles of control and eradication and states the policy and rationale for control and eradication. The plan leaves Australia well prepared to respond to the discovery of an exotic honey bee disease or pest.
The AusVetPlan technical response plan for bee diseases is also presently being used by AQIS as a guide for assessing risks and developing protocols associated with proposals to introduce to Australia lucerne pollinating leafcutter bees, Megachile rotundata, for commercial purposes. For these proposals, AQIS has also consulted and met with relevant industry groups, CSIRO, Government bodies and the Australian Nature Conservation Agency (ANCA). These highly commended actions show the positive benefits that can flow from having a set of comprehensive strategies in place for responding to exotic pathogens and pests of a particular insect.
It should be noted that much of the underpinning research on Asian honey bee species and their diseases is financed by ACIAR. This PNG-based research is one example of many funded by ACIAR which either reduced the risk of exotic diseases or pests entering Australia or places the country in a better position to cope with these incursions should they eventuate (see Section 5.1.3).
'Weeds are an insidious, complex problem of national dimensions. Every year they exact an enormous toll on the Australian economy and environment, a toll that is steadily increasing while our capacity to deal with it is piecemeal and deteriorating.
In 1992, Australia spent $463 million on herbicides compared with $138 million on insecticides and $66 million on fungicides. This was just part of the estimated $3,300 million annual costs of weeds to the nation. This estimate itself only represents the direct and indirect costs in lost production and control, and does not take into account the externalities of erosion, non-target environmental damage, health and safety issues and the effect of weeds on the natural environment, biodiversity, the urban environment, amenity values and tourism.
Virtually every agricultural industry in Australia (collective worth in excess of $21,000 million) is affected, either by lost production, contamination of produce or by poisoning of livestock. Some recent estimates of direct and indirect costs include; $600-800 million to NSW, $400 million to Victoria, $650 million to South Australia and nationally, $600 million to the wool industry. Exotic weeds are responsible for over 90% of these losses. Product quality is an issue of increasing importance for export markets and high herbicide usage sits poorly with Australia's clean green image and community expectations.
Compounding this situation is the rapidly increasing incidence of herbicide resistance. Unknown twenty five years ago, this phenomenon is now widespread, with more than 2,500 properties affected in Australia and increasing numbers of cases of multiple resistance across many herbicide classes.
In Australia's natural environment, the devastating impact of weeds on native vegetation and associated native fauna has only begun to be appreciated in recent years and information is still very incomplete. Some 15% of Australia's flora of 15-20,000 species are alien, of which approximately half invade native vegetation and a quarter are already, or likely to become, weeds.
In a country where the natural environment is one of the biggest attractions and ecotourism is the fastest growing sector of the tourism industry, the increasing degradation of our natural bushland by invasive alien species is of serious immediate and long term concern to this industry.
The Landcare movement is one of the recent success stories of community concern and involvement and has identified weeds as their biggest single issue. Weeds are a symptom and an agent of land degradation and landowners are desperate for advice and the means to ameliorate the problem. Weeds are also the biggest single concern for urban bushland community groups.
Several weeds are toxic to humans and, while sensible precautions prevent tragic results, an increasing number of weeds are being implicated in debilitating allergic reactions. The pollen of widespread species, (e.g. ryegrass, Paterson's curse) is a major source of irritation and species like parthenium weed can cause major problems with members of the population who become sensitised.
To further exacerbate a near disastrous situation, new species are entering Australia and establishing at the rate of 4-6 species p.a. and, because of the lag time that is normal between establishment and realisation of weedy potential, there are already enough species sitting waiting to pose new weed problems into the foreseeable future. Further, weed spread is usually exponential. Minor problems today become major problems tomorrow.
Collectively, weeds pose a problem of enormous magnitude for Australia, a problem that is on the verge of being out of control in many areas. Their management is crucial to Ecologically Sustainable Development and to Conservation of Biodiversity, both fundamental planks of Government policy for agriculture and the environment'.
(CRC for Weeds Management Systems, 1995)
For a discussion of the search for solutions to weed problems, see R J Adair (1995) in Conserving Biodiversity ed. R A Bradstock, Surrey Beatty, NSW. pp 194-201.
In the last 20 - 30 years a significant number of new plant diseases have appeared in Australia. The best known example of economic importance was the appearance of stripe rust of wheat (Puccinia striiformis) in 1978. This disease added significant costs to wheat production in Australia, both in terms of direct yield losses during epidemic years and through the added costs of breeding for disease resistance. The prevention of initial invasion is a highly cost effective method of protecting Australian crops and the natural biota from fungal disease. As with insect pests, eradication campaigns are difficult, and their success is largely dependent on how quickly after initial invasion a disease is identified. It is therefore important to identify risk areas and to formulate strategies to deal with outbreaks of disease that are potentially catastrophic to a particular Australian industry. Although resistance to stripe rust of wheat has been bred into many Australian wheat varieties, those grown in Western Australia are still susceptible because the disease has not reached there. A sudden introduction of stripe rust into Western Australia could have disastrous effects on the wheat harvest in that State. The risk from bulk grain imports as stock feed was referred to in Section 3.1.
Rice production in the Murrumbidgee Irrigation Area in New South Wales is another example of an effective and profitable primary industry at risk from introduced diseases. Currently, the rice industry has none of the fungal diseases that beset rice production in other parts of the world. This is because of a combination of different growing conditions and geographic isolation. While these factors, particularly the difference in climate for Australian rice production, have led to the introduction of varieties that are suitable for Australian growing conditions, these varieties contain no resistance to fungal pathogens and there is a danger of complacency, because these diseases are currently not present in Australia. Contingency plans need to be developed to ensure the survival of the rice industry should fungal diseases of rice appear.
To date, Australia has been fortunate in that few introduced diseases have moved on to native Australian species: Phytophthora cinnamoni in Western Australia is a major exception. A number of exotic diseases are known that will attack Australian native species. These include various diseases of Myrtaceous species that will attack Australian species in the same family. A particularly good example is that of Puccinia psidii (guava rust) which attacks a range of eucalypt species growing in plantations in Brazil and other South American countries. In those situations epidemics of the pathogen cause substantial defoliation. In South-East Asia, several canker diseases, unknown in Australia, have been found in plantations of Eucalyptus camaldulensis. In some plantations in Vietnam the effect of these is so great that plants are reduced from a forest tree to a multi-stemmed mallee form. None of these pathogens currently occur in Australia but their arrival could have substantial and irreversible effects on natural communities.
Again, as with insect pests, the north of Australia needs to be recognised as a major potential source of incursions and an increase in vigilance in this area for introduced diseases should be a major AQIS priority. The development of emergency plans for fungal diseases that become established in Australia should also be a high priority.
Papaya ringspot virus, an aphid-transmitted potyvirus, was first found in Australia in 1991. It causes a debilitating disease of all commercial papaya cultivars, and severely limits pawpaw production in most tropical and sub-tropical countries, especially in south-east Asia. Its appearance in Australia caused considerable concern, especially because it was first found in a small crop near Brisbane International Airport, suggesting that it had come from overseas and somehow breached quarantine controls at the airport.
PRSV and another potyvirus, watermelon mosaic virus 1 (WMV1), which was first recorded in Australia in 1978, are biotypes of the same virus species. They are only distinguished by their host ranges; WMV1 infects a wide range of cucurbits, but not papaya, whereas PRSV infects papaya and few cucurbits.
Staff at the Queensland University of Technology (in collaboration with the A.N.U.) sequenced the virion protein genes of several isolates of PRSV and WMV1 from Australia and the likely source countries overseas. They found that the Australian PRSV isolates had probably evolved from an Australian WMV1 isolate, and probably on only a single occasion. Thus PRSV probably did not breach quarantine, but evolved from WMV1 within Australia. It seems that this has happened independently in other countries, as more recent QUT/ANU research has shown that in Thailand there is also the same close relationship between PRSV and WMV1 isolates, as in Australia.
This example illustrates the principle that all apparent quarantine incursions should be followed up to try to determine if and how the quarantine barriers were breached.
Alfalfa mosaic virus was probably introduced into Australia in lucerne seed early in the period of European colonization. It was recorded from white clover in Queensland in 1945 and subsequently elsewhere. However, sporadic surveys of lucerne in south-eastern Australia in 1966-75 did not detect it. Incursion of the spotted alfalfa aphid and blue-green aphid was first reported in 1977 and the pea aphid was first reported in 1981. The main Australian cultivar of lucerne, Hunter River, proved to be very susceptible to colonization and damage by these aphids, and so large amounts of seed of American lucerne cultivars, selected for their resistance to aphids, was imported. Six out of eight seed lots imported directly from the USA, and tested at the ANU proved to have up to 1.9% AMV infection. The three immigrant aphids all proved to be vectors of AMV, infection of lucerne crops throughout south-east and western Australia has greatly increased, and the virus has become common in a wide range of crop and weed species. AMV causes a 5-20 % decreased yield in lucerne.
This illustrates the need for quarantine vigilance at all times and that, giving in to short term pressure from industry, may merely alleviate short term pain for a long term cost.
The history of quarantine in Australia as it pertains to human health, has been covered in Section 2.1.1. The human quarantinable diseases recognised by the Quarantine Act 1908 were 'Smallpox, Typhus Fever, Yellow Fever, Plague and Cholera'. Arriving ships were required to notify the Quarantine Officer of the presence aboard of any quarantinable diseases, and the Quarantine Officer often boarded the ship with the pilot and carried out inspections of any sick persons, and sometimes of all passengers and crew for evidence of smallpox, before allowing disembarkation to proceed.
In the 1950s the administration of human quarantine measures was changed in response to the replacement of ships by aircraft as the principal method of introduction of people to Australia. Inspection of incoming passengers concentrated on their possession of a valid certificate for vaccination against smallpox and, if they came from Africa or South America, a certificate of vaccination against yellow fever. With the global eradication of smallpox in 1977, the requirement for smallpox vaccination disappeared. Shortly after this, the administrative apparatus for quarantine of human diseases was dismantled, but in 1982 microbiologically secure ward isolation and laboratory facilities were established at Fairfield Hospital in Melbourne to facilitate the investigation of exotic human diseases.
Currently (1996), the quarantinable human diseases are yellow fever, plague, cholera, rabies and four of the viral haemorrhagic fevers (Crimean-Congo, Lassa, Ebola and Marburg). The problem of yellow fever and the viral haemorrhagic fevers are dealt with by the issue of warning notices to incoming passengers, and suspected cases may be placed under quarantine. As a precaution against the importation of arthropod vectors of human diseases, every Australian international airport maintains mosquito control measures within a 400 metre perimeter, and Australia requires all arriving aircraft to be disinsected using approved methods.
The Academy believes there are, at present, no major issues of concern for human disease organisms. However, it does note that, with the transfer of human quarantine from the Department of Health to DPIE, there has been an erosion of capacity in this aspect of quarantine. For example, medical officers have been reduced in number and are normally not present at major ports of entry; rather, they are available on call. With global warming and changing ecological suitability of regions of Australia for disease vectors, and with the increased movement of people, especially in northern Australia, we could find ourselves unprepared to deal with a new threat to human health. Indeed, it is possible that Australia, more by default than the result of some explicit policy, might lose the ability to anticipate a human health challenge and to prepare adequately for such an eventuality. (For a discussion of the increasing likelihood of human pandemics, see Mimms. 1995. Epidemiol. Infect. 115: 377-386.)
The Academy is concerned that Australia, more or less by default, is lowering its capacity to exclude the entry of exotic diseases of humans. It recommends that the Government's advisory council contain at least one medically qualified member.
Protection of Australia's farm animals from exotic diseases has been a major function of the quarantine authority since the last century and continues to be so. AusVetPlan was established as a contingency plan to deal with an outbreak of FMV, blue tongue or rabies and it is discussed at Section 5.3. The recent occurrence of Bovine Spongiform Encephalopathy (BSE) in Britain has served to emphasise the inestimable value of Australia's isolation. BSE is closely related, if not identical to Scrapie, a disease of sheep that is endemic in Britain but absent from Australian sheep. In an editorial of 28 March 1996 the Canberra Times draws the important lesson from this:
'If ever Australia needed a lesson on the importance of maintaining the highest quarantine and other safety standards for its food products it is surely provided by the disaster facing Britain in the mad-cow disease panic.
The Howard Government must take note: user pays, privatisation and other economic rationalist nostrums have no place in this area. This government must act for the national interest.'
While the occurrence in 1994 of an undescribed equine virus and its transfer to humans may not come under the terms of the present review, it does illustrate in dramatic form the response of the relevant institutions to an unexpected disease outbreak. In this case the virus was isolated, characterised and demonstrated to be the disease agent within four months (K. Murray et al. 1995. Science, pp 268, 94-97) of its first appearance. This was a signal vindication of the establishment of the Australian Animal Health Laboratory and the role it can play in any future occurrence.
Lessons from escape of the Rabbit Calici Virus (RCV) from Wardang Island in October 1995 are still to be fully assessed. The Academy expects that other submissions to this review will deal with animal disease organisms more fully.