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The Papaya Fruit Fly - A Failure of Quarantine
Tom Bellas
Consultant to
Science, Technology, Environment and Resources Group
On 17 October 1995, Mr John Crawford, a pawpaw (papaya) grower near Cairns,
found fruit fly maggots infesting his crop. The culprit was identified as
the papaya fruit fly, a species not previously reported from mainland Australia.
This fruit fly has been described as the worst pest of fruit in Asia and
the Pacific. Surveys of the surrounding areas found flies in Mossman to
the north, Bingil Bay to the south and inland at Mareeba.
A quarantine zone was established that extended 500 kilometres along
the coast and up to 200 kilometres inland. Susceptible fruit and vegetable
fruits-and that meant almost all varieties produced in the area-leaving
the quarantine zone for markets in the south had to be treated with insecticide.
Japan and New Zealand banned the import of fruit from the area.
Little is known about the biology of this species and how it will adapt
to Australian conditions. The papaya fruit fly is thought to be capable
of extending its range southwards as did the Queensland fruit fly last
century. The flies are claimed to infest all of the varieties of fruit
grown in the area except pineapples and to infest vegetables such as tomatoes
and melons. Observations to date indicate that it is out-competing the
Queensland fruit fly and attacks fruit that this fly rarely attacks making
it a far worse pest than the indigenous species. Control costs will be
substantially greater than they have been with the existing fruit fly
pests.
The flies almost certainly arrived in Cairns in fruit brought from areas
to the north. The nearest infestation was on islands in northern Torres
Strait 800 kilometres away. It is clear from the distribution of the flies
in October 1995 that they had been present for one to two years.
Male lures provide a sensitive and efficient detection system for the
papaya fruit fly. Traps had been in place in the Cairns area as well as
in other places in northern Queensland from 1976 to 1988 when they were
removed. Despite a recommendation contained in a report of the Horticultural
Policy Council in 1991 that was considered by the Standing Committee on
Agriculture in February 1992 the traps were not replaced.
The reason why this decision was taken is unknown since the papers of
the Standing Committee are confidential. If the reason was related to
cost, the savings of less than $200 000 per year on traps is far less
than the estimated $40-50m cost of an eradication program. Even if an
eradication attempt does not proceed, the cost of measures needed to control
this new pest will quickly amount to more than the cost of a system of
detection traps.
Fruit flies have invaded many areas around the world and they have been
eradicated many times. An efficient procedure for eradication has been
developed using male annihilation, female suppression and the release
of sterile insects. These techniques have been used to eradicate Mediterranean
fruit fly from Carnarvon and the Queensland fruit fly from Perth.
Eradication is easiest to achieve if the infestation is found when the
extent of the invasion is small and before the population has increased
which it would have been in this case if traps had been in place. The
Horticultural Policy Council was concerned that '. . .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 arrival of the papaya fruit fly in Cairns has confirmed
their worst fears.
Population suppression measures were commenced within a month of the
discovery of the fly and these measures have greatly reduced the population.
At the time of writing (May 1996), there has been no decision made about
whether to proceed with an attempt to eradicate the fly.
In December 1995, funding was announced so that monitoring traps for
exotic fruit flies could be set out near airports and seaports in northern
Australia. While that action is too late for the papaya fruit fly, there
are several other pest species in areas to the north of Australia that
would become problems if they were allowed to become established. An adequate
system of traps to detect exotic fruit flies backed up by contingency
plans for their eradication and a mechanism for rapidly putting those
plans into effect will prove of great benefit to Australian agriculture.
Responses to pests and diseases of animals are covered by the Australian
Veterinary Emergency Plan (AUSVETPLAN). There is no comparable plan for
pests and diseases of plants nor does there appear to be any group with
the responsibility to prepare contingency plans for pests like the papaya
fruit fly.
It is highly desirable that there be a co-ordinated program to produce
contingency plans and preparedness plans for pests and diseases of plants.
This program could be organised through the Standing Committee on Agriculture
and Resource Management and use the resources and expertise of the Australian
Quarantine and Inspection Service, the Bureau of Resource Science, State
Departments concerned with agriculture, and the CSIRO.
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ABARE Australian Bureau of Agricultural and Resource Economics
ACIAR Australian Centre for International Agricultural Research
AQIS Australian Quarantine and Inspection Service
AUSVETPLAN Australian Veterinary Emergency Plan
CSIRO Commonwealth Scientific and Industrial Research Organisation
DPIE Department of Primary Industries and Energy
HPC Horticultural Policy Council
Medfly Mediterranean fruit fly
NAQS Northern Australian Quarantine Strategy
OTA Office of Technology Assessment, US Congress
PHC Plant Health Committee
QFF Queensland fruit fly
SCA Standing Committee on Agriculture
SCARM Standing Committee on Agriculture and Resource Management
SIRM Sterile Insect Release Method
SIT Sterile Insect Technique
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Chemical names of specific fruit fly lures
cue-lure 4-(4-acetyloxyphenyl)-2-butanone
methyl eugenol 1,2-dimethoxy-4-(2-propenyl)-benzene
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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 impact of fruit flies on Australian agriculture, Horticultural
Policy Council, April 1991.
The papaya fruit fly, Bactrocera papayae, was found infesting
pawpaw at Yarrabah, near Cairns, in October 1995. A quarantine zone was
promptly established extending 20 kilometres around the Cairns Post Office.
Within ten days the fly was trapped at locations to the north, west and
south of Cairns and the quarantine region had been extended to cover a
region about 500 kilometres along the coast and up to 200 kilometres inland
(see Figure 1). Japan and New Zealand imposed bans on the import of produce
and controls on movement of produce from the area were established within
Australia.
Thus were the first few days after the confirmation that a new, highly
damaging fruit fly pest had arrived on the Australian mainland. The papaya
fruit fly is described by Dr R. A. I. Drew of the Queensland Department
of Primary Industries, one of the world's leading investigators of fruit
flies, as the worst fruit pest in the whole of Asia and the Pacific.
Within days of the discovery a team of people was assembled in Cairns
to investigate the extent and the severity of the infestation. On 16 November
a program was initiated to control the fruit fly (AQIS Bulletin 1995a).
Finance has been provided through the Standing Committee on Agriculture
and Resource Management (SCARM) to enable investigations into the species'
host preferences and into the possible hosts among indigenous fruits.
There are still many areas where our knowledge of the papaya fruit fly
is deficient.
At the time of writing (May 1996), the control program begun in November
has already had an impact on the populations of the fly in areas that
it has infested and the numbers of flies in these areas has been much
reduced. But flies have been found another 50 kilometres further south
at Kennedy.
This paper provides background information on the arrival of this new
insect pest, examines how the the invasion has become as serious as it
is, and looks at the chances of success in repulsing a pest that has the
potential to have a major adverse impact on Australian horticulture.
The name 'fruit fly' has been applied to two groups of flies.
To orchardists and entomologists it means those flies that lay their
eggs in immature or ripening fruits so that their larvae can feed and
grow within the fruit. The damage arising from the feeding of the larvae
makes the fruit unmarketable. These flies are placed in the taxonomic
family Tephritidae (1). These are the fruit flies that are the subject
of this paper.
To geneticists it means Drosophila melanogaster and related
species that have been the subject of their study for many years. The
larvae of most of the Drosophilidae feed on fungi and while the larvae
are found in fruit it is only in those fruits that are over-ripe and decaying
and usually fallen. Entomologists prefer the names ferment flies
or vinegar flies for these insects (Carne et al. 1987).
The papaya fruit fly, Bactrocera papayae, is placed in the family
Tephritidae within the order Diptera (the true flies). There are at least
4 000 species in this family of flies, the great majority of which have
larvae that feed on fruits or on seed-producing heads of plants of the daisy
family (Asteraceae). Of these 4 000 species around 10 percent would be classified
as pests and around 10 percent of these (i.e., about 40) as major pests.
The adults of most species of fruit flies can live for two to six months,
are capable of flying many kilometres-even across water-and produce many
young. Many of the species of fruit flies are restricted to one species,
or a very few closely related species, of host plants. It is from among
this group that biological control agents have been brought to Australia
for the control of Bathurst burr, Crofton weed, Bitou bush and thistles.
Fruit flies are of major significance in almost all fruit growing areas
of the world either because they are already present or because they are
capable of establishing in areas presently free of them. The major pests,
e.g., the Mediterranean fruit fly, attack a wide range of fruits and have
established themselves in regions far from their native range. Quarantine
restrictions have been imposed around the world as countries try to prevent
the spread of the pests into new regions.
Figure 1: North Queensland (4)
The great majority of species in the family Tephritidae are placed in
one of four sub-families: Trypetinae; Tephritinae (seed flies); Dacinae;
and Ceratitinae. The species in the sub-family Dacinae are found predominantly
in tropical and sub-tropical regions and are associated with soft fruits
from a very wide range of plants. The more than 800 species in the Dacinae
are found in Africa (200 species), Asia/South East Asia (300 species)
and the South Pacific (300 species). All of the pest fruit flies native
to Australia belong to the Dacinae.
Several synthetic chemical lures for fruit flies have been found through
accidental discoveries and systematic searching. The Dacinae can be divided
into three groups: those species attracted to methyl eugenol; those attracted
to cue-lure; and those not attracted to either of these compounds (Drew
& Hooper 1981; the systematic names of the two chemicals are given
on page iii). At normal population levels only males are found in traps
baited with methyl eugenol or cue-lure. The range of attraction of methyl
eugenol for papaya fruit fly males is probably only a few tens of metres
downwind although because of the mobility of these flies individuals from
much further away will be trapped over time as they fly into the area
of attraction of the lure (Cunningham 1981).
Several chemicals that attract males of the Mediterranean fruit fly
(in the sub-family Ceratitinae) have been discovered but none is as effective
as the two chemical lures that are active for the Dacinae.
Methyl eugenol and cue-lure provide a sensitive and efficient tool for
detecting low populations of those species of fruit flies that respond
to these chemicals.
The papaya fruit fly is one of a number of pests that were until recently
known collectively as the oriental fruit fly, Bactrocera dorsalis.
Flies with this common name have been recognised for many years as the worst
pest among the Dacinae. They damage fruit in much of east, south-east and
south Asia and on islands to the north of Australia. The oriental fruit
fly has been transported to and has established itself on islands across
the Pacific; it reached Hawaii in 1946. This fly has been eradicated from
California more than a dozen times. This name, however, was applied to a
group of species all very similar in appearance-forming a species complex.
The more than fifty members of the dorsalis-complex occupy many
areas of Oceania and south-east Asia and also infest a wide range of host
fruits. Not all members of the species complex are pests. That there is
a species complex has been known for many years but it was only in 1994
that a definitive publication on this group of flies was published (Drew
& Hancock 1994). Thus the name Bactrocera papayae only dates
from that year.
The home range of the papaya fruit fly is south-east Asia-southern Thailand,
Malaysia and Indonesia-where it infests a wide variety of indigenous and
introduced fruits. Many studies have been conducted on the oriental fruit
fly but because of the confused taxonomy it is not always clear as to
which of the species within the complex was being studied. Thus results
of research on the fly present in Hawaii (which is the true oriental fruit
fly) need not apply to the papaya fruit fly. What is known is that the
papaya fruit fly attacks a wide range of fruits and attacks them earlier
in the ripening process than most other species of fruit flies.
After mating, females lay their eggs just under the skin of the host fruit.
These entry points are known as 'stings'. In summer around Cairns the eggs
will within 36 hours hatch into larvae (known as maggots) which feed and
burrow into the fruit. Up to 30 maggots of the oriental fruit fly have been
found in one fruit. The damage caused to the fruit by the feeding larvae
can lead to premature fruit drop. After about seven to ten days, depending
on the temperature and the quality of the food, the larvae leave the fruit
and burrow into the ground to pupate. Adults emerge from the pupae about
ten to twelve days later. Adults are sexually mature after about a week
or two and can live for three to four months. Provided the females have
access to protein and mates they can reproduce throughout their life. In
the oriental fruit fly the potential fecundity is over 1000 eggs per female
and this is likely to be true for the papaya fruit fly as well. The long
reproductive life of a female means that it can still be laying eggs when
its great grandaughters are attacking their first fruits.
Eighty-four species in the Dacinae have been described from Australia (Drew,
1989). All of the species occur in tropical or subtropical parts of the
country spread across the wetter northern areas and down the east coast.
All are associated with moist forests and depend on the soft fruits produced
within those forests. Several of the species are pests. The Queensland fruit
fly, Bactrocera tryoni, is the most widespread and damaging of
the Australian species. It has become established in New Caledonia and in
some of the Society Islands including Tahiti. It also became established
on Easter Island from where it has been twice eradicated.
Before Europeans arrived with their fruit trees the Queensland fruit
fly occurred probably no further south than northern NSW; a report on
Sydney in 1819 commented on the quality and quantity of stone fruits with
no indication of the presence of pests. But by 1853 maggoty fruit was
reported from Kiama south of Sydney and the present range extends into
East Gippsland (see Drew, 1989). The Queensland fruit fly now infests
inland towns in NSW. In addition the flies have established themselves
many times in irrigation areas along the Murray valley and Adelaide but
they have been eradicated as many times. It was recently eradicated from
Perth (Yeates, 1990) after its first appearance in the metropolitan area.
The Queensland fruit fly in north Queensland breeds continuously provided
suitable fruit is available. It is capable of passing through seven generations
a year in the northern part of its range but in East Gippsland there is
only one generation per year. Around Sydney there can be three or more
generations per year and numbers can increase rapidly over a summer (Meats,
1989).
The Queensland fruit fly's presence has meant that access to many markets
for Australian fruit has been denied or made difficult because of control
and disinfestation measures that have to be applied to comply with the
requirements of importing countries. Several other indigenous species
are rated as significant pests (see Table 1) and other species are occasional
or minor economic pests. There are restrictions and prohibitions on movements
of fruit and vegetables within Australia which aim to prevent the penetration
of the Queensland fruit fly and other species into areas where they do
not normally occur.
Table 1: Indigenous Fruit Fly species that can be major economic pests.
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Name of species
Bactrocera Infests Location Synthetic lure
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aquilonis many fruits N & NW Aust. cue-lure
bryoniae capsicum, mangoes E Qld cue-lure
cucumis melons, tomatoes, pawpaws E Qld, NT none known
jarvisi several fruits NW Aust to NSW none known
melas several fruits Central & SE Qld cocue-lure
musae bananas NE coast, PNG methyl eugenol
neohumeralis many fruits NE coast, PNG cue-lure
tryoni many fruits E coast cue-lure
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Extracted from Economic fruit flies of the South Pacific (Drew et al. 1982)
Across Australia the sum of the costs of fruit fly-induced crop losses plus
the costs of pre-harvest controls and regulatory costs were estimated in
1994 to be in excess of $150m yearly. When the loss of international markets
due to fruit flies was included the estimated cost to Australia was of the
order of $300m per annum (SCARM Workshop, 1995).
The Mediterranean fruit fly, Ceratitis capitata, found its way
to Western Australia before the turn of the century. After Western Australia
it then appeared in New South Wales where it became a major pest around
Sydney. For reasons not known but possibly associated with an increasing
abundance of the Queensland fruit fly, the Mediterranean fruit fly became
less common and the last sighting in NSW was in 1941. It is still present
as a major pest in Western Australia.
In 1974 flies collected on the Cape York Peninsula were identified as
Bactrocera frauenfeldi, a species known from Papua New Guinea
as a pest of mangoes. The arrival of this species in Australia called
attention to the possibility of the arrival of pest species from areas
to the north. In mid-1975 a trapping program specifically for the oriental
fruit fly and the melon fly (Bactrocera cucurbitae) commenced.
The discovery in November 1975 of a fly identified as the oriental fruit
fly from Melville Island brought fears that there had been another invasion.
However this fly was not found in commercial fruits and an intensive study
found that it was not the oriental fruit fly but an indigenous species
restricted to one local fruit, Opilia amentacea (Morschel 1979).
This species is now known as Bactrocera opiliae.
A series of trapping stations was established across the northern coastline
from Derby to the Torres Strait. This program, known as the Northern Monitoring
Program, also incorporated monitoring for the oriental screw worm and
was largely conducted by the States and the Northern Territory using funds
provided by the Commonwealth Government.
In 1983 on Christmas Island, nine males of oriental fruit fly were collected
at methyl eugenol baits as part of a survey conducted by the Western Australian
Department of Agriculture. These specimens were later determined to be
the papaya fruit fly (Drew & Hancock 1994). This is the earliest known
incursion onto Australian territory.
In 1987 a major review of quarantine in Australia was conducted by a
committee headed by Professor David Lindsay of the University of Western
Australia. The report of the review was published in 1988 (Department
of Primary Industries and Energy 1988). The review was conducted after
the reorganisation and consolidation of quarantine functions within the
Department of Primary Industries and Energy.
In an interim report (Quarantine Review Committee 1987) the committee
noted the special problems associated with Australia's northern coastline.
The use of motors on boats and the use of aircraft had increased movements
of people and produce between the islands of Torres Strait and between
the islands and the mainlands of Australia and Papua New Guinea. There
was also an increasing movement of pleasure boats and yachts in the area
as well as increased international and domestic tourism. The nearness
of Papua New Guinea and the changing practices and variety of agriculture
there would thus cause an increase in the number and types of pests that
are that much closer to Australia.
As a result of this inquiry there was established in 1989 the Northern
Australia Quarantine Strategy (NAQS). It was under this program that the
Australian Quarantine and Inspection Service (AQIS) began to conduct surveys
in Papua New Guinea in 1989 and also in Irian Jaya, the easternmost province
of Indonesia adjacent to PNG. Also in 1989 a series of trapping stations
was set up across Torres Strait. Initially there were eight: Boigu, Saibai,
Yam, Badu, Thursday, Yorke and Murray Islands, and also at Bamaga on Cape
York to monitor the populations of fruit flies and to check on the species
present.
In August 1995 the NAQS maintained monitoring stations on thirteen islands
in Torres Strait and six locations on northern Cape York Peninsula as
well as six stations in Western Australia and nine in the Northern Territory.
The Torres Strait stations were on the following islands: Badu, Boigu,
Darnley, Dauan, Deliverance, Gabba, Horn, Murray, Saibai, Stephen, Thursday,
Yam, and Yorke, with all but Deliverance being checked monthly. The southernmost
of the six stations on the mainland was Bamaga (Nairn, 1995) (see Figure
2).
In April 1992 the presence of Bactrocera papayae was reported
from Merauke, Irian Jaya, to the south-west of PNG. In May 1992 the species
was collected in Papua just over the border from Irian Jaya (AQIS Bulletin
1992).
By March 1993 the papaya fruit fly had reached Australian territory
in Torres Strait when it was found on Boigu Island just off the Papuan
coast and on Darnley Island further to the east. Within a few weeks traps
had been placed on another 58 islands and further flies were trapped on
Saibai, Dauan and Stephen Islands. Control measures were commenced and
an eradication program applied on the two islands furthest from the Papua
New Guinea coastline since reinfestation was certain on the islands close
to the coast. Darnley and Stephen Islands were declared free of Bactrocera
papayae after no flies were trapped for several months. In early
1995 flies were again detected on Darnley and Stephens Island and soon
afterwards on Murray and Yorke Islands. It is thought that seasonal strong
winds had carried the flies to these islands from Papua New Guinea. A
control program was initiated on these four islands (AQIS Bulletin 1995b).
In October 1995 came the announcement that the flies had been found
near Cairns. The extent of the infestation, from Mossman in the north
to Bingil Bay to the south and inland to Mareeba would indicate that the
flies had been present for many months and had dispersed widely. Cairns
seems to have been the hub of the infestation.
It is unlikely that the flies that were responsible for the original
infestation near Cairns arrived unaided. The nearest natural infestation
was on islands in the northern Torres Strait. And while fruit flies have
been known to cross more than 100 kilometres of water it is far more likely
that a batch of infested fruit was brought into Cairns from an already
infested area to the north. The fact that flies have not been found between
Mossman and Cape York, nor on the islands just to the north of the Cape
shows that they did not island-hop across Torres Strait onto the mainland.
The most likely route for the entry of the papaya fruit fly into Cairns
is by aircraft from one of the Torres Strait islands but other routes
such as pleasure craft cannot be discounted.
Figure 2: Torres Strait
In south-east Asia the papaya fruit fly infests a wide range of commercial
and native fruits (White & Elson-Harris 1992). Many of those tropical
fruits are also grown in north Queensland. The fly is said to be capable
of breeding in all fruits except pineapples; and most vegetable fruits (tomatoes,
squash etc.). The rainforests of Queensland have many species of plants
in the same plant families as those that occur in south-east Asia so it
is likely that this fly will be able to maintain itself on rainforest fruits.
Traps placed in rainforest have captured male papaya fruit flies but it
is not known whether the flies are breeding in the forests.
The papaya fruit fly attacks fruits that the Queensland fruit fly rarely
infests, such as mango and pawpaw. In fruits that both species attack
the newcomer appears to be out-competing the Queensland fruit fly. This
may be because the papaya fruit fly attacks fruit a few days earlier than
the Queensland fruit fly and thus gains an advantage.
The original observation at Yarrabah was in pawpaw. The grower had not
had to spray because of fruit flies for several years so when he saw an
infested fruit he asked for advice. It was his observation that brought
the infestation to notice.
The home range of the papaya fruit fly is Southern Thailand, peninsular
Malaysia, Borneo and some other Indonesian islands. It has a more tropical
distribution than Bactrocera dorsalis, the oriental fruit fly,
which has a distribution range to the north of this species (Drew &
Hancock 1994).
The Queensland fruit fly proved to be able to adapt to cooler climates
in extending its range from northern NSW to east Gippsland. It seems that
the genetic makeup of the species allowed it to adapt to the cooler conditions
(Meats 1989). If this is also true of the papaya fruit fly then it could
range much further south than the range in south-east Asia would suggest
and many important fruit growing areas could be infested by this new pest.
The gross value of annual production in Queensland of fruit and vegetables
that are potential hosts of the papaya fruit fly is estimated at $486m
(ABARE 1995). Around 70% of the produce is sent outside the State, mainly
to southern destinations, but there is a growing market for this produce
overseas. Sales to southern markets from within the quarantine zone are
continuing following post-harvest disinfestation of the fruit and vegetables.
The re-establishment of overseas sales will depend on convincing the importing
countries that adequate control measures are in place and that disinfestation
procedures currently in use to combat indigenous flies (e.g., for mangoes,
by heating them with steam) will also work for this new pest. Regions
which are currently free of papaya fruit fly will have to establish a
monitoring program to prove that the fly is not present to permit current
exports to continue.
Fruit flies have been eradicated from areas where they have invaded more
times than any other group of insects. The first time this was achieved
was in 1929 in Florida when the Mediterranean fruit fly made its first incursion
into North America. The earlier methods relied on fruit removal and widespread
spraying with arsenical insecticides. Since then efficient methods have
been developed to achieve eradication and it has become almost routine (Bateman
1982).
Three methods have been developed which are usually applied in combination
to achieve eradication.
Annihilation of males. This method makes use of the synthetic
chemical lures that have been discovered. Traps baited with a lure and
containing an insecticide (usually malathion) are placed throughout an
area (see Figure 3). Any males that are attracted to the lures are killed.
Because the females can mate with several males a very large proportion
(more than 95%) of the males has to be removed to reduce the size of the
next generation. Provided enough traps are installed this is not difficult
and reductions by more than 99% have often been achieved. Because the
flies can live for months it may be several weeks before there is a decline
in the number of females.
This method used alone was successful in eradicating the oriental fruit
fly from the 85 square kilometres island of Rota in the Marianas Islands
in 1965. The usual technique is to load a mixture of the lure and an insecticide
into a medium which can be a block of porous material, a length of cord,
or viscous fluid formulations (Cunningham 1989).
Insecticidal bait sprays (female suppression). This method
is based on the need in female flies for a meal of protein before they
can develop their full load of eggs. By providing a source of protein
and adding insecticide to it, females can be selectively removed from
the population. The most common lure is a hydrolysed protein solution.
The mixture can be placed as individual lures or spot baits or more commonly
sprayed over the foliage of host trees (Bateman 1982). This method is
capable of achieving eradication but requires an intensive effort (Scribner
1983).
Sterile Insect Technique. Neither of the preceding methods
is selective. The use of male lures means that other fruit fly species
that respond to the same chemicals will be attracted to the baits and
the protein hydrolysate is attractive to other fruit flies as well as
other types of insects. The third method is selective in that only flies
of the pest species are the target of the technique.
Figure 3: Fruit Fly Trap
The sterile insect technique (SIT)-or sterile insect release method
(SIRM) as it was earlier called-was conceived by E. F. Knipling in the
1930s and was first applied against the New World screwworm fly in the
USA in the 1950s. The theory behind the technique is that if sufficient
sterile male flies are released then the chances of a wild fertile fly
mating with a fertile male are reduced. Matings with a sterile male would
result in sterile eggs and no progeny. The method worked very well against
the screwworm because in that species each female mates only once. However
it has been shown that even with species where females mate many times,
as with fruit flies, provided enough sterile males are provided the technique
can still work. The method requires the production of very large numbers
of insects that are sterilised by irradiation before their release into
the environment (Gilmore 1989).
It is best to apply the SIT when the population is low. This can be
during a part of the year when the numbers are normally low or it can
be achieved by applying first one or both of male annihilation or bait
spraying. The lower the population the easier it is to achieve the high
ratio of sterile males to fertile males necessary for the method to work.
The people who conducted the successful eradication of oriental fruit
fly from the island of Guam took advantage of the fact that there had
been two hurricanes which had drastically reduced the amount of fruit
on the island and had blown most of the fruit flies off the island.
The ratio of sterile males to fertile males should be as high as possible
but there is no firm information on a minimum value. A ratio of 50 or
more to 1 appears to be necessary for success: values lower than this
have rarely given the desired result (Hooper 1982). It is suggested that
for the Queensland fruit fly a ratio of around 1000:1 would be required
(Horticultural Policy Council 1991, p. 106). Eradication is not claimed
until no flies are trapped at lures for a period of time equal to three
generations under the prevailing conditions.
Most of the successful eradication exercises have been conducted on
islands or with infestations caught early before the numbers have increased
or the flies have dispersed very far. The oriental fruit fly has been
eradicated from California at least 13 times: in each case the flies had
arrived from Hawaii. This species has been eradicated from Japan where
it was present on several islands in the vicinity of Okinawa. The Japanese
campaign commenced in 1968 but was not completed until 1986. The melon
fly has been eradicated from Rota and a few of the southern Japanese islands.
Fruit flies have been eradicated many times in Australia. The Queensland
fruit fly has often infested fruit growing areas in southern NSW and in
Victoria and South Australia over the years and in each case eradication
has been achieved. Adelaide has been the scene of many successes. A major
eradication was achieved in Perth in 1989-1990 after the first ever infestation
was discovered in the Perth metropolitan area.
An area of about 300 square kilometres was treated. The program involved
using all three of the methods outlined above. The population was suppressed
using bait blocks (with cue-lure as the attractant) and protein foliage
sprays and then, over a period of ten months, 1 504 million sterile flies
were released. The operation commenced in February 1989 when the flies were
discovered and the program was declared successful when no further flies
were discovered after December 1990. The operation had a budget of $5m.
It had been estimated that the annual cost of control measures in addition
to those already in place to combat the Mediterranean fruit fly would be
about $2m per year (Yeates 1990; Ayling 1989). Some of the techniques used
in this campaign were developed in the successful project to eradicate the
Mediterranean fruit fly from Carnarvon in 1984 (Fisher 1985). Traps baited
with cue-lure are now in place to detect any further arrivals of the Queensland
fruit fly in and around Perth.
The Mediterranean fruit fly was discovered in Brazil in 1904. From that
infestation the fly has spread over most of South America and into Central
America. It was detected in Costa Rica in 1955. An attempt was made to stop
it spreading northwards but in 1975 it appeared in Honduras, El Salvador
and Guatemala. In 1977 it was detected in Mexico in the State of Chiapas
just north of the border with Guatemala. In order to protect the large Mexican
horticultural industry and to prevent the pest's movement northwards an
international program was launched with the support of international organisations
(Organizacin de los Estados Americanos, Organism Internacional Regional
de Sanidad Agropecuaria, Food and Agriculture Organisation, International
Atomic Energy Agency) and the co-operation of three countries: Guatemala,
Mexico, and the USA. The stated aims of the program were to halt the spread
of the fly, to eradicate it from Mexico and Guatemala and ultimately to
eradicate it from Central America. By 1979 the flies had penetrated into
the next State north (Oaxaca) about 250 kilometres north of the border and
efforts to eradicate the flies were intensified.
From 1977 the program employed bait spraying from the ground and from
the air, and confiscation of fruit from infested trees to reduce the population.
Fumigation of fruit was conducted to prevent spread of the flies. Vehicles
were inspected and fumigated at ports of entry into Mexico. A large mass-rearing
facility was constructed at Metapa in Mexico and came into operation in
1979. After some initial fine tuning this facility from 1981 to 1985 produced
on average 500 million sterile flies or more per week (Schwartz et al.
1989). In addition to servicing the local campaign several thousand million
flies were provided to California where two infestations had been discovered
in 1980 and where a campaign was conducted until 1982 when the insect
was declared eradicated (see Appendix) (Scribner 1983).
At its peak the project was being conducted over 4 600 square kilometres.
Northward expansion of the fly was stopped by 1980. In 1982 the fly was
declared eradicated from Mexico and the major campaign moved into Guatemala.
However small numbers of flies were occasionally found in Mexico and some
areas had to be re-treated.
Because of social, political and financial problems the ambitious long
term objective of eradicating the fly from Central America has been indefinitely
postponed. The program at its peak in 1981 cost US$19m a year but this
was reduced to about US$10m per year within two years. The money was provided
by Mexico and the USA (Schwas et al. 1989).
An analysis of the economics of the program in the Mexico/Guatemala border
regions was reported in 1989 (Vo 1989). The direct control costs were given
as being US$62.76m. The estimate of the benefit/cost ratio with the benefits
calculated up to 1991 is given as 49:1. A similar analysis had been conducted
for the campaign against the Mediterranean fruit fly in Santa Clara county,
California, that began in 1980. High and low benefit scenarios were estimated
as at 1991 and the benefit/cost ratios are calculated as between 19.62 and
12.75 at these limits (2). The figures quoted in the original publication
(Conway 1982) have been reassessed in 1991 (OTA 1993).
In December 1995 the Australian Bureau of Agricultural and Resource
Economics published a report on a cost-benefit analysis of a proposed
eradication program (ABARE 1995). The analysis was conducted using a set
of fourteen fruits and vegetables (3) which account for 84% of Australia's
total gross value production of potential papaya fruit fly hosts. The
lack of knowledge of the biology of the papaya fruit fly in the Australian
environment means that firm predictions cannot be made of the possibility
of eradication so there are considerable uncertainties in the analysis.
If the papaya fruit fly is capable of spreading into southern fruit-producing
areas then high benefits are obtained. If however the fly will not spread
much further southwards then lower benefits arise. The analysis used a
variety of scenarios. These comprised two estimates of the cost of the
eradication campaign, differing estimates of the chances of success of
the eradication and allowing only half the number of sprays recommended
by the Queensland Department of Primary Industries. The results showed
that the publicly funded eradication campaign yielded positive net benefits
for most of the scenarios considered.
Usually a decision would wait until firmer information was available
but under the circumstances a decision may have to be made assuming the
worst case as being most likely.
The area infested by the papaya fruit fly in north Queensland by early November
(from Mossman, 70 kilometres north of Cairns, to Bingil Bay, 110 kilometres
south, and to Mareeba, 30-40 kilometres inland) is already comparable to
the area treated in Mexico. Use of both male lure baited traps and protein
bait treatments can drastically reduce the population of the papaya fruit
fly. But it will do little to reduce the area of infestation or stop the
fly from invading new territory particularly if the flies can breed in rainforest
fruits.
The conditions in Queensland offer some advantages for eradication over
southern Mexico. The rainforests are bounded to the west by dryer country
and few fruit trees thus limiting the spread of the flies in that direction.
The social and political conditions that caused problems around the Mexico/Guatemala
border do not exist (Schwarz et al. 1989). The population is well educated
and the fruit growers are eager to participate.
The first steps towards eradication were initiated on 16 November 1995
by the Queensland Department of Primary Industries which is overseeing
a program using methyl eugenol baited traps and protein bait spot treatments
in areas where breeding populations have been identified or where they
could become established (AQIS Bulletin 1995a). 'The next stage involves
a study by relevant Commonwealth and State agencies to examine the feasibility
of broad-scale eradication measures' (from the same bulletin). These measures
would involve the use of the sterile insect technique and the building
of a mass-rearing facility for the production of the very large number
of flies that will be required for the area that has been infested.
As in Mexico the first aim of a SIT program would be to prevent the
extension of the area infested: in this case towards the large fruit growing
areas to the south. The first step has been the establishment of a quarantine
zone from which only fruit that has been treated is allowed to leave the
quarantined area. Thus the first areas to be covered using the SIT method
would be just to the south of the area known to contain flies. As fruit
fly-free zones are established then the treatment area would be moved
northwards until fly-free areas are reached. The southern Torres Strait
islands would be treated if by that time the flies have invaded them.
Any population suppression measures using insecticide have to be applied
in advance of the SIT area so that sterile flies are not removed before
they have a chance to do their job.
The number of sterile flies required and hence the size of the breeding
program (and the size of the factory) will depend on the population of
the papaya fruit fly. In orchard and urban areas control measures can
lower the population as has already been achieved but there are greater
problems, including effects on non-target organisms, in reducing the population
in rainforest areas. If it becomes necessary to attempt to attack the
flies in the rainforest then the attack will have to be conducted so as
to minimise damage to non-target insects and other animals. The decision
on the feasibility of eradication will depend on accurate estimates of
the numbers of papaya fruit flies in the rainforest.
An analysis of the cost of conducting an SIT program was conducted for
a Horticultural Policy Council report (Horticulture Policy Council 1991
p. 118). For the production of 20 million flies per week for at least
40 weeks a year the annual production costs were estimated to be $230
500. The construction and set-up costs of the factory were calculated
as $475 000. The costs for conducting the eradication program were estimated
as $382 000. These estimates were made in 1989 for eradication of the
Queensland fruit fly in southern Australia. These costs were compared
with the then costs of eradication activities in NSW, South Australia
and Victoria which were calculated as $590 000 a year. In addition there
were suppression campaigns which cost an additional $400 000 a year. An
advantage of the proposal was that when sterile flies were not required
for eradication they could be redirected towards suppression thus giving
overall savings. These figures were estimates made for small outbreaks.
The successful eradication of the Queensland fruit fly from 300 square
kilometres of Western Australia operated with a budget of $5m over two
years.
An eradication campaign against the papaya fruit fly would be substantially
larger than any conducted previously in Australia. Figures of $35m and
$52.5m were used in the ABARE benefit-cost analysis as estimates of the
cost over five years.
If the papaya fruit fly cannot be eradicated then in those areas it occupies
it will have to be controlled to enable the production of fruit and vegetables
to continue. The aim of control is to maintain the population at a level
below which the damage can be tolerated ('the economic threshold').
A well established program for the control of indigenous fruit flies
already exists (Beavis et al. 1989; Thwaite et al. 1995). Where the flies
are endemic, or where an infestation has become established, cover sprays
with systemic insecticides are the usual recommendation for most fruits.
Systemic insecticides are absorbed by the plants and will translocate
into the fruits where the fruit fly maggots are hidden from other types
of insecticides. Male annihilation and protein bait sprays and spot treatments
can all have their place in the control of fruit fly infestations, particularly
in those areas where fruit flies are not always present (Bateman 1982).
The SIT method could have a place in the control of small outbreaks and
the maintenance of zones free of flies (Horticulture Policy Council 1991,
pp. 74-76).
The recently established Tri-State Fruit Fly Strategy will employ the
SIT method to control and eradicate the Queensland fruit fly in the Riverina,
Sunraysia and Riverland areas of south eastern Australia so as to maintain
fruit fly-free status that will allow the export of produce without the
need for disinfestation.
Mr John Crawford, the grower who found the first infestation by the
papaya fruit fly just south of Cairns is reported to have said that he
had not had to use sprays for several years (Roberts 1995). He will now
have to undertake measures in order to control this new fruit fly and
it has been estimated that even small growers will face additional costs
of $15 000 a year (Granger 1995). A substantially greater effort will
be needed than before if the papaya fruit fly becomes established.
In some fruits cultural practices also play a role in reducing the impact
of fruit flies. In bananas the technique of bagging the bunches at an
early stage affords significant protection from fly attack. Removing infested
fruit from the trees and the collection and treatment of fallen fruit
are important factors in reducing the numbers of flies that emerge.
Exports of fruit from fruit fly infested areas are still possible provided
that the importing country can be convinced that the produce has been
treated to ensure its freedom from living flies. Various disinfestation
methods currently in use include dipping or flood-spraying with insecticides;
fumigation; low temperature storage; and various heat treatments by exposure
to heated vapours or hot air; or by dipping in hot water, all of which
add considerably to costs incurred by the producer. Irradiation has been
proposed as a method for disinfestation but it is not currently used.
In 1904 the Western Australian Government sent Mr George Compere to
search for biological control agents for the Mediterranean fruit fly which
by then had established itself as a severe pest in the state. He was the
first of many to conduct such searches. He introduced several potential
agents but few became established and little impact on fly populations
was observed. While no fruit fly pest has ever been under complete classical
biological control the use of these agents has contributed to significant
reductions in populations of some pest species. The most successful was
the introduction of parasitic wasps to Hawaii where populations of oriental
fruit fly and the Mediterranean fruit fly were reduced and the incidence
of attack on the less favoured hosts of the flies declined. The major
agent was the wasp Fopius arisanus but when this species was
introduced into Australia its effect was negligible on the Queensland
fruit fly even though it was successfully established (Waterhouse 1993).
It is not known whether this species of wasp has any effect on the papaya
fruit fly.
Sex pheromones. In many species of insects interactions between
the sexes are governed by volatile chemicals known as pheromones. In moths
the females produce blends of chemicals which result in males of the right
species being able to find the females from many metres distance. These
substances have been used to specifically detect males of pest species to
provide early warning of their presence and in some cases have provided
a means of controlling the pest. In southern districts of NSW and in Victoria,
the oriental fruit moth, a major pest of peaches and nectarines, is controlled
without the application of insecticides by using this approach (Thwaite
et al. 1995).
Tephritid fruit flies are known to possess sex pheromones. From a gland
attached to the hind gut the males produce a blend of chemicals that is
released during courtship. The identity of the chemical compounds involved
has been established for several species. While the chemicals undoubtedly
have a role it seems that sight is the most important factor in establishing
contact between the sexes. To date pheromones have not been used in controlling
the pests although a place may still be found for them in an integrated
pest management system.
Host odours. Female flies have to be able to locate fruit so
that they can lay their eggs. Further the fruit has to be at the right
stage of development to provide the best environment for the growth of
the larvae. Fruit flies use both sight and smell. Smell is of more importance
with flies with narrow host ranges. The apple maggot fly, Rhagoletis
pomonella, of eastern USA, is attracted by odours produced by apples
and in the olive fly, Bactrocera oleae, a major pest of olives
around the Mediterranean, smell plays a major role. In both of these species
the performance of traps is improved by the addition of host odours. Nothing
is known of the behaviour of the papaya fruit fly in this regard.
Improved lures. While protein hydrolysate has been very useful
it loses its effect after a two or three days exposure on leaves. The
search for lures with improved performance is underway in several places
around the world. There are similar projects in Australia and, while the
immediate target is the Queensland fruit fly, a successful result will
be of benefit in the program against the papaya fruit fly.
Three pest fruit fly species have found their way to Australia: the Mediterranean
fruit fly late last century probably from Africa or India; and two species
from north of Australia, the mango fly by 1974 and now the papaya fruit
fly. There are several other species of fruit flies in Asia, Papua New Guinea
and Oceania that could become serious pests if they established themselves
in Australia (Table 2).
The melon fly, Bactrocera cucurbitae, is rated as one of the
world's most serious pests and the most important pest of vegetables especially
melons (Waterhouse 1993). It is present in Irian Jaya, mainland Papua
New Guinea and several islands to the east of there as well as on Hawaii.
Soon after emergence the adults are capable of very long flights-30 to
60 kilometres but even longer flights over water have been recorded. The
150 kilometres gap between Papua New Guinea and Cape York is not a substantial
barrier to this species.
The oriental fruit fly, Bactrocera dorsalis, has very similar
capabilities to the papaya fruit fly. It is a major pest in Hawaii and
from there makes regular incursions into California. This fly could infest
many fruit growing areas in southern Australia. It would be wise to maintain
both cue-lure and methyl eugenol baited traps at all cities which receive
direct flights from Honolulu.
While it is easy to detect those species that respond to the synthetic
chemicals cue-lure and methyl eugenol there are two species (Bactrocera
atrisetosa and B. decipiens) that are listed in Table 2
that do not respond to either of these. Like the Australian fruit flies,
B. jarvisi and B. cucumis, their presence will only
be detected after they are found in fruits at the new location and have
already been in the area for some time.
Table 2: Pest species of fruit flies known from areas to the north of Australia
-------------------------------------------------------------------------------
Species name BactroceraRegion Hosts Chemical lure*
----------------------------------------------------------------------------------------
albistrigata SE Asia many fruits cue-lure
atrisetosa PNG melons none known
cucurbitae PNG/Asia melons cue-lure
caudata SE Asia melons cue-lure
decipiens PNG melons none known
dorsalis Asia/Hawaii many fruits cue-lure
facialis Tonga many fruits cue-lure
kirki Tonga, W Samoa many fruits cue-lure
passiflorae Fiji, Tonga many fruits cue-lure
tau SE Asia melons cue-lure
trivialis PNG many fruits cue-lure
umbrosa SE Asia/PNG/ Melanesia many fruits methyl eugenol
xanthodes Fiji, Tonga many fruits methyl eugenol
----------------------------------------------------------------------------------------
Adapted from
The impact of fruit flies on Australian horticulture (Horticultural Policy Council 1991).
* Drew 1989; Drew (pers. comm.)
In the Lindsay Report of 1988 it is pointed out that no quarantine system
can guarantee total exclusion of pests and diseases while there is trade,
movement of people, natural movement of pests and diseases, and intentional
or unintentional breaking of the law. The Report suggested a system of
risk management to allow the quarantine system to be most effective within
these constraints (Lindsay Report, chapter 3).
The NAQS, whose origin arose from the considerations of this committee,
has been active in education about quarantine among the people who live
in Torres Strait and other parts of northern Australia and also among
travellers through the region (Baldock 1989). Information about quarantine
has been provided via various media: radio and videos, and also in print
to air travellers, to schools, and to the 18 communities that live on
the islands of Torres Strait (AQIS Bulletin 1992). The public awareness
created by this 'Topwatch' program has been rated a definite achievement
(Nairn & Muirhead 1995).
The papaya fruit fly could have arrived in Australia as adults using
their own flying abilities perhaps assisted by favourable winds as has
been suggested for their arrival on islands in the eastern Torres Strait
in 1995 (AQIS Bulletin 1995b). This can be called a natural process and
although such arrivals cannot be prevented contingency plans can be in
place to repulse the invasion. The alternative is an assisted passage
for the eggs or maggots in fruit brought into the country by a traveller.
There is some possibility of preventing such occurrences.
The disposition of the thirteen monitoring traps in Torres Strait and
the six on the mainland (see Figure 2) indicate that the expectation was
that if there was an invasion by the papaya fruit fly or other fruit fly
species that they would progress from island to island across the strait
in the form of a natural invasion. If the assisted passage was from island
to island these traps would have provided warning but they could not if
the entry by-passed these traps altogether.
This possibility was considered in the Horticultural Policy Council
Industry Report No 3, The impact of fruit flies on Australian horticulture,
published in April 1991, which contained a recommendation (No 14) that
Detection systems for threatening exotic species should
be established around the most likely entry points (major and minor seaports
and airports) throughout Australia.
Some port cities already had extensive monitoring traps in place (Adelaide,
Darwin and Perth) and the report names Sydney, Newcastle, Brisbane and
Cairns as 'obvious high risk areas where detection systems are seriously
needed'. The report suggested that each trapping station should have three
traps: one cue-lure, one methyl eugenol and one capilure (a synthetic
chemical lure for the Mediterranean fruit fly).
The report was submitted to the then Minister for Primary Industry and
Energy who passed the report onto the Standing Committee on Agriculture
(SCA). The SCA asked for a critical assessment by the Plant Health Committee
(PHC) which analysed the report and found Recommendation 14 (and most
of the others) acceptable. The PHC response was considered by the SCA
at the meeting held in February 1992. Despite this recommendation
no traps were put in place between that date and October 1995.
It has not been possible to ascertain what discussion occurred at this
meeting or the reasons why no action was taken as the papers of the meeting
are regarded as confidential and will only become available after thirty
years have elapsed.
The Queensland Department of Primary Industries had placed monitoring
traps in Cairns and some other coastal cities between 1976 and 1988. This
system was funded by the Commonwealth Government. The trapping at these
locations was discontinued when AQIS took over the direct management of
the northern Australia surveys.
The HPC Report expressed concern that detection trapping was not being
conducted at many of the most likely entry points (Horticulture Policy
Council 1991, p. 48).
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.
That is just what appears to have happened with the papaya fruit fly
at Cairns where it is likely that the fly has been present for at least
one year and perhaps as long as two years.
The Report stated that the detection system should be an integral part
of Australia's quarantine system and that it should be funded by AQIS,
planned in consultation with fruit fly biologists and carried out by staff
of the local state departments of agriculture (Horticulture Policy Council
1991, p. 49).
On 14 December 1995 a media release announced the provision of $14.7m
over three years to strengthen quarantine barrier surveillance in northern
Australia. Among the measures mentioned was '. . .the development of lures
and monitoring for exotic fruit flies around airports and seaports. .
.' (Collins 1995).
If monitoring for exotic fruit flies had been in place at Cairns in
1994 the probability of detecting the papaya fruit fly soon after its
arrival would have been high, as the monitoring systems installed in California
for the oriental fruit fly have proven. The infestation would most likely
have been confined within Cairns and a relatively minor campaign for its
eradication would have been required. The delay in its discovery has fulfilled
the fears of the authors of the Horticultural Policy Committee's report.
As far as we know the papaya fruit fly is the latest pest insect to arrive
in Australia. Since 1971 forty-eight species of insects from overseas are
known to have become established in Australia and the great majority of
these are pests (Clarke 1996, pers. comm.). It is precisely because they
are pests that they have been noticed.
There may well be many other insect species that have arrived but they,
being more cryptic, have not announced themselves. Early in 1995 the cause
of damage to greens and fairways at the Steelworks Golf Course in Newcastle
was identified as a South American mole cricket known to cause many millions
of dollars damage to turf annually in the USA. This pest is now known
to have been in Australia for at least thirteen years since a specimen,
unidentified at the time, was collected in 1983.
In the USA over the period 1980 to 1993 a total of 159 insect and mite
species of foreign origin were introduced or first detected. For the 62
species where a pathway had been identified the great majority arrived
unnoticed on plants. Of these 159 species 41 were rated as harmful introductions.
This list does not include those insects introduced in the same period
as biological control agents (OTA 1993).
No similar list is as yet available for Australia. Dr G. M. Clarke of
the Division of Entomology, CSIRO, has been seconded to the Animal and
Plant Health Branch of the Bureau of Resource Sciences to produce a report
entitled "Exotic insects in Australia: introductions, risks, and
implications for quarantine". His report is expected to be completed
in June 1996.
There are many insects which would prove important pests if ever they
were able to establish a foothold in Australia. A list of pests of tropical
crops, prepared in 1991, is included in the report of the review of NAQS
(Nairne and Muirhead 1995). For some of these potential pest insects there
are specific lures such as sex pheromones but for the majority the only
weapon is vigilance.
Cue-lure and methyl eugenol make the detection of many of the pestiferous
fruit flies an easy task. Unfortunately the detection of almost all the
other potential new pests is usually only made after the invasion when
the pest has established itself in its ecological niche and calls attention
to itself, as indeed was the case with the papaya fruit fly at Yarrabah,
and as was also true for another two insects that will prove very damaging
over many parts of Australia.
The silverleaf whitefly, Bemisia tabaci biotype
B, was first detected in Queensland in October 1994. It is now well established
in that State as well as the Northern Territory and New South Wales and
has been detected in Tasmania. It is a damaging pest to many vegetable
crops as well as a wide range of ornamentals. It is on ornamental plants
that it has travelled the world. International trade in poinsettia has
been a major route.
It has had its major impact on crops grown under intensive agriculture
and in greenhouses. In the Imperial Valley in California between October
1991 and February 1992 crop losses to this insect amounted to US$111m
and in addition there were about 6 000 fewer jobs in January 1992 than
there were in January 1991 (De Barro 1995). By 1994 another 3 000 local
jobs had disappeared and total damage was then estimated as US$300m (OTA
1995, p. 117).
The silverleaf whitefly has a wide host range (more than 600 species),
can increase in numbers very rapidly, is resistant to several insecticides,
is highly damaging to its hosts, and it is a vector of several plant viruses
that, up to date, have lacked an efficient vector in Australia (De Barro
1995).
The western flower thrips, Frankliniella occidentalis
was detected in Perth in May 1993 on mixed flower crops (AQIS Bulletin
1993). Restrictions on the shipment of flowers to eastern States were
imposed but the insect quickly appeared in the east as well. The thrips
on the east and west coasts are not genetically identical so it seems
that there have been two separate invasions, both likely to have been
on imported cut flowers (Stapleton 1995). This thrips infests a wide range
of crops and its feeding causes growth distortions in the host plants.
It can also act as a vector for viruses. It is already resistant to a
range of insecticides.
Both the silverleaf whitefly and the western flower thrips are expected
to be at least as costly as the papaya fruit fly. And as with most insect
pests that have found their way to Australia they are here to stay and
Australia's horticulturists will have to learn to survive in their presence.
The Quarantine Review Committee (Lindsay Report 1988) recommended that immediate
action should be taken to develop a strengthened, planned and co-ordinated
approach to responding to outbreaks of exotic pests and diseases of plants
(Recommendation 34). The Committee further recommended that the Bureau of
Rural Science (a forerunner of the Bureau of Resource Sciences) should be
responsible for developing plans for outbreaks of exotic pests and diseases
of animals and plants and for co-ordinating responses (Recommendation 43).
Responses to pests and diseases of animals are covered by the Australian
Veterinary Emergency Plan (AUSVETPLAN) which is managed within the Livestock
and Pastoral Division of the Agriculture and Forest Group in the DPIE.
There is no comparable plan for pests and diseases of plants nor does
there appear to be any group with the responsibility to prepare contingency
plans for pests like the papaya fruit fly.
Currently each outbreak of a plant pest is considered after it occurs
by the SCARM and the Plant Health Committee which reports to the Standing
Committee. The PHC usually forms a Consultative Committee (as it did for
the papaya fruit fly) to obtain expert advice on the particular pest or
disease. Although the Queensland Department of Primary Industries responded
promptly after the identification of the papaya fruit fly, control and
suppression with funding through SCARM commenced four weeks afterwards
(almost a generation on) and a decision on the implementation of eradication
procedures is still under consideration (more than three generation times
after the discovery). The question of funding is always contentious.
The papaya fruit fly has a generation time of four to five weeks. The
suppression measures put in place have greatly reduced the population
of the flies but these measures are unlikely to prevent natural spread
of the flies at the periphery of their range where suppression measures
are unlikely to have been applied so that the area of the infestation
will be increasing.
The major inhibition to the development of contingency plans for pests of
plants is the very large number of organisms that could become pests if
they were able to establish in Australia. This was recognised by the Quarantine
Review Committee (Lindsay Report 1988, p. 114) but nevertheless it still
recommended that the effort should be made. The Committee recommended that
the then Bureau of Rural Science be responsible for this task but this was
never taken up by them or their successors.
The NAQS maintains a target list of exotic insects that is currently
being revised and brought up to date. The insects are grouped under high,
medium and low priority headings. There are no contingency plans even
for those insects in the high priority group. The recent review into NAQS
(Nairn and Muirhead 1995) contained as recommendation No 17
that NAQS scientists develop preparedness plans for
all the targeted pests and diseases of plants and work with other stakeholders
to develop contingency plans for a limited number of more important targets,
over a period of five years.
The NAQS reviewers noted that it is often difficult to find an effective
forum for development of such plans until a crisis developed but suggested
that the NAQS scientific staff are in an excellent position to develop
these plans (Nairn and Muirhead, p. 28). Whether the current scientists
have the resources or the time to apply to the development of the plans
is questionable. The NAQS list covers those insects that occur in areas
to the north but insects from other areas could be covered by AQIS or
by people in State departments.
It is highly desirable that there be a co-ordinated program to produce
contingency plans and preparedness plans for pests and diseases of plants.
This program should be organised through SCARM and use the resources and
expertise of AQIS, BRS, State Departments concerned with Agriculture,
and the CSIRO. The costs of preparing these plans will be minuscule compared
with the damage that results from the arrival of a single pest like the
silverleaf whitefly on an unprepared horticultural industry.
Another approach is to anticipate the arrival of a pest. It is to Australia's
advantage if a pest that occurs in a neighbouring country that is capable
of establishing on Australian territory is brought under control in that
country because then there is less likelihood that it will find its way
to Australia and, if it does, then a control method is already available.
This approach has been undertaken with some insect pests which will
at some time in the future arrive in Australia. The banana skipper caused
much damage in Papua New Guinea but an ACIAR funded program conducted
by the Division of Entomology, CSIRO, has introduced an effective biological
control agent that has greatly reduced its incidence (CSIRO 1992, p. 50).
The Russian wheat aphid when it arrives in Australia will have a very
damaging effect on wheat production just as it did in the USA and in South
Africa. A CSIRO program based in the Republic of South Africa has identified
biological control agents that will be introduced as soon as possible
after the discovery of the aphid here (CSIRO 1992, p. 47). The sex pheromone
of a sugar cane borer causing damage in Papua New Guinea has been identified
and this can be used to give early warning of the presence of the pest
and it might even be able to be used as the basis of a control program
(Whittle et al. 1995).
The present invasion is a major rather than a minor problem because of the
delay in detecting the papaya fruit fly on mainland Australia caused by
the failure to have monitoring traps in place in the vicinity of airports
and seaports.
The Lindsay Report noted that a 'no risk' policy was untenable and undesirable
and that a policy of 'acceptable risk' was preferred. It also noted that
the assessment of risk should be scientific and objective.
If the withdrawal of traps from Cairns in 1988 and the refusal to reinstate
them in 1992 despite the recommendation of the Horticultural Policy Council
was based on risk analysis, then surely the arrival of the flies in Torres
Strait should have rung the alarm bells and led to a reversal of those
decisions. The failure to do so has produced the current situation.
In early 1996 a trap baited with cue-lure at Cottesloe in suburban Perth
caught one male melon fly. The trap was part of an array across the metropolitan
area that was established to detect new invasions of Queensland fruit fly
after the successful eradication of the species from Western Australia in
1990. More intensive monitoring was established but no further melon flies
were detected. It is unknown how the fly came to be in Western Australia
but the lack of further captures after two months indicates that there is
not a breeding population. But for the necessity to monitor for the Queensland
fruit fly the arrival of this species in Western Australia would have passed
unnoticed.
On the other side of the continent a shipment of mangoes and chillies
from Fiji was seized and destroyed this year following the detection of
fruit fly larvae in the chillies. This was despite the shipment having
been supposedly treated with ethylene dibromide as a disinfestation treatment
for fruit flies. Imports of ethylene dibromide-treated produce from Fiji
were suspended (DPIE, Primary Resource, Issue 96/2).
By the end of March male papaya fruit flies had been found over a wide
area but still well within the quarantine zone. Surveys have been conducted
for flies breeding in wild guava which is widespread throughout the hinterland
of Cairns but only in the vicinity of Cairns, Mossman and Mareeba have
breeding populations of papaya fruit fly been found. There have been no
flies found breeding in rainforest fruits which indicates that there will
not be significant populations of flies within the rainforests. Population
suppression measures have greatly reduced the population relative to its
level at the time of its discovery. No decision has been made about proceeding
with eradication. A meeting of the Consultative Committee is scheduled
for June (by which time there will have been about seven generations of
flies since the discovery at Yarrabah) (R. A. I. Drew, pers. comm.). Meanwhile,
the Federal Government and Queensland are funding the $6 million papaya
fruit fly detection and suppression program up to 30 June 1996.
- The tephritid fruit flies discussed in this report are given their
current scientific names. Prior to 1989 all of the species now in the
genus Bactrocera were placed in the genus Dacus and literature before
then will refer to these species under this generic name (Drew, 1989).
- The estimates were published in 1982 before the program has been brought
to finality. The cost is given as US$64m whereas the final cost was
close to US$100m (Scribner 1983). The benefit/cost ratios are thus overestimated.
If the calculated ratios are in direct proportion to the assumed costs
then the benefit/cost ratios calculated with the actual cost are 12.56
and 8.16.
- Bananas, mangoes, pawpaw, citrus, apples, pears, wine grapes, table
grapes, grapes for dried vine fruit, apricots, peaches, tomatoes, pumpkins
and cucumbers.
- On 20 October 1995 a quarantine zone was declared over the area 20
km around the Post Office at Cairns. On 26 October a regulation was
published (No 301 of 1995) to establish a larger zone above 18 20'
south and on 5 November, with regulation No 305, the zone was extended
to 19 south. Regulation No 301 contained an error since it referred
to a point on longitude 144 15' west and the regulation
was probably defective because of that. The zone shown in the map assumes
that the intended point was on longitude 144 15' east.
Mediterranean fruit fly eradication from California, 1980-1982:
an example of the difference between early and late detection.
On 5 June 1980 males of the Mediterranean fruit fly were trapped at
two locations in California.
In Los Angeles the identity of the one fly caught was established the
next day. More traps were installed and more flies captured nearby thus
confirming the presence of a breeding population. The infestation was
discovered in its first or second generation and at the time of the discovery
was confined to one loquat tree. Because of the success of a SIT program
in 1975 it was decided to use this method again. In July the release of
sterile flies commenced and continued until October. The flies were released
over an area of 258 square kilometres corresponding to a circle of radius
about 8 kilometres around the site of the infestation. Just over 205 million
flies were released and eradication was declared in December 1980. This
area treated was entirely urban.
In Santa Clara county at the southern end of San Fransisco Bay the two
flies were not identified until twelve days later. Subsequently flies
were found throughout a 13 square kilometres area. The infestation was
probably in its third or fourth generation. Until 1980 it was believed
that the Mediterranean fruit fly could not survive during the cooler months
in the Bay area and traps were removed in autumn and replaced in late
spring. It is suggested that the flies had arrived about the time that
the traps were removed and consequently they were not discovered until
at least two generations had passed (Gilmore 1989).
The area of infestation was initially underestimated and the number
of sterile insects released was too small to be effective. One major problem
was the detection of wild flies among the very large number of sterile
flies captured in monitoring traps. Even though the sterile flies were
marked with fluorescent dusts an inefficient procedure caused an underestimation
of the number of fertile flies. This in turn led to low population estimates
and the release of too few sterile flies.
Bait spraying was commenced early in the campaign but there were problems
of access to backyard fruit trees. The area of infestation increased until
it covered several counties around the southern end of the Bay. The total
area that required treatment was almost 3 400 square kilometres. After
it was realised that the SIT was failing it was decided that aerial spraying
should be the method employed.
As well as technical problems with the eradication method and the way
in which it was conducted there were numerous others. Because the area
was largely urban there was much opposition to the proposed spraying.
There were many public meetings opposing spraying and eventually court
proceedings. The State Governor initially refused permission to conduct
aerial spraying but the possibility of a declaration of a total quarantine
on California caused the Governor to grant permission and spraying was
allowed. The spray program commenced in July 1981 and continued for just
on 12 months. The flies were declared eradicated in September 1982 (Scribner
1983).
This successful eradication program became an immense undertaking and
cost about US$100m. In contrast the Los Angeles infestation which was
found early the cost was only a small fraction of this amount.
There were many organisational and technical problems that hindered
success (Scribner 1983). A detailed account of the campaign and its problems
is given by Jackson and Lee (1985). An account of problems, particularly
those of the different approaches of the scientists and managers, that
gave rise to misunderstandings and conflicts within this program, is given
by Lorraine and Chambers (1989).
The northern and the southern incursions offer a salutary lesson in
the advantages of catching an infestation early. Although both infestations
were eradicated there was probably a hundred-fold difference in the costs
due to finding the Santa Clara infestation just a few months too late.
Successful as the 1980-1982 campaigns were there was only a short respite.
In 1986 a single fly was captured in Los Angeles which under the established
protocols was not enough to initiate action. But every year since then,
there have been further catches and despite extensive efforts at eradication
using mainly the Sterile Insect Technique there are at present some 4
100 square kilometres of the Los Angeles basin under quarantine.
All of the recent eradications of the Mediterranean fruit fly have depended
on the widespread application of pesticides before applying the SIT (Carey
1994). In this largely urban area this option has not been applied. Unlike
the chemical lures for the oriental fruit fly and the papaya fruit fly
there is no really efficient lure for males and this has proven a major
weakness both in early detection of new areas of infestation and the attempts
to eradicate the flies. It has been suggested that the Mediterranean fruit
fly is on its way to becoming established in the Los Angeles basin (Carey
1991).
In 1983 State quarantine officials discovered that large quantities
of illegal produce was being brought into California through Canada. One
shipment of longans had travelled from Seattle via Vancouver, Toronto,
New York and Miami, where it was repacked into Florida boxes, to California
where it was detected at a border inspection station. The identification
of this previously unidentified route of infestation and a change in tactics
will, it is hoped, lead to eradication of this pest (Dowell 1994).
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Acknowledgements
I thank Carol Kenchington of the Parliamentary Library and Jon Prance of
the Black Mountain Library for their assistance in locating and retrieving
information from a wide variety of sources. Dr R. A. I. Drew provided the
photograph of the female papaya fruit fly taken by Mr Steve Wilson of Mt
Nebo, Queensland.
Comments to: web.library@aph.gov.au
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19 July, 2004
by the Parliamentary Library Web Manager
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