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
------------------------------------------------------------------------------------
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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by the Parliamentary Library Web Manager
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