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Fruit fly detections in Auckland - Expert Q&A

Published: Thu 21 Feb 2019 09:43 AM
Two different species of exotic fruit flies have been found in Auckland in the past week. Both pose a risk to New Zealand's horticulture industry and the threat is unlikely to disappear.
News of the second discovery, a species native to Tonga that was found in Ōtara, broke yesterday afternoon. Meanwhile, biosecurity restrictions remain in place in Devonport after a Queensland fruit fly was discovered last week. RNZ reported that the Ministry for Primary Industries has ordered an independent review of its biosecurity systems.
The SMC prepared a Q with biosecurity experts.
Dr Karen Armstrong, Senior Research Officer, Bio-Protection Research Centre, based at Lincoln University.
The Queensland fruit fly has so far been detected five times in the upper North Island in the past decade. Are we likely to see more Queensland fruit flies turning up in New Zealand in the future? Why?
"Yes, we will inevitably see more Queensland fruit flies arrive in New Zealand. This won’t necessarily be more frequently, unless their numbers in SE Australia erupt, but the threat will not disappear.
"Regardless of the relatively extensive pre-, at- and post-border systems in place, it’s impossible to secure New Zealand against this pest which can go undetected inside a piece of fruit, and enter the country through many different routes."
The Queensland fruit fly has been described as one of the biggest threats to New Zealand horticulture. What crops are most at risk from the fruit fly?
"This species is a generalist, with a vast range of fruit that it can develop on and damage. The fruits most likely to be attacked after initial introduction will depend on what is available close to where the first adults emerge.
"But some hosts for Queensland fruit fly are better than others. From a New Zealand commercial perspective apples might be at most risk. Second only in export value to kiwifruit (NZD 1.7 billion), apples (NZD 0.7 billion) are a preferred host. As well as damaging the fruit this species is able to develop well in the fruit and the pest numbers can easily grow. Similarly at risk are citrus, stone fruit, pears, berries and avocado crops.
"Kiwifruit and grapes for wine, on the other hand, are not known elsewhere as preferred hosts for the Queensland fruit fly. They can be attacked but the flies develop poorly such that the numbers are unlikely to proliferate as they do with apples. For example, in grapes overseas, significant fruit damage is only seen when Queensland fruit fly numbers are extremely high. Therefore these crops in New Zealand, because of their high export value, may be the impacted largely by loss of market access and management restrictions."
A second type of fruit fly - a facialis fruit fly - has been found in Auckland. How worried should the horticulture industry be about the discovery of this second fruit fly?
"The horticultural industry should not be more worried than they will already be for the Queensland fruit fly. Fruit fly reaching New Zealand is inevitable, and this is that time of year.
"But with the pre- and at-border systems we have in place, the number getting here is substantially less than it would otherwise be. With the experience we have and world-class surveillance and response systems in place, we stand a high chance of preventing establishment of these pests, as we have before.
"This second species is a significant economic pest in its home range, confined to Tonga. It has been intercepted in New Zealand before. But, in our favour, it does not show the same invasive tendency like the Queensland, Mediterranean and Oriental fruit flies or have as broad a host range, although its hosts do include citrus, peach, capsicum, mango and avocado. The climate in south Auckland will not be as favourable as it is in Tonga."
Is it possible that there are other potentially-damaging species in New Zealand that haven't yet been detected?
"If there are other potentially damaging exotic species here, as yet undetected, it would be hard to know until they became an obvious problem. And for fruit flies that clearly hasn’t been the case. Detections and eradications have always been successful."
What’s the worst-case scenario if a population of Queensland fruit fly were to establish itself in New Zealand?
"New Zealand and Chile are the only major horticultural producing countries in the world that are free from fruit fly species that attack commercial fruit.
"Therefore, no matter which type of fruit the fly was shown to be established on, New Zealand would lose its pest-free status.
"In the immediate term, our biggest fresh fruit exports of kiwifruit and apples, and others such as cherries, avocados and capsicum, could be locked out of trade for a period with their largest markets in Asia, the Americas and Europe until eradication was proven. These regions do not have this fruit fly species which would put their own fruit industries at risk.
"The worst-case scenario would be if eradication was not possible. New Zealand’s standing on the global fresh fruit market would be severely undermined, and our competitive advantage and premium returns eroded through pre-export treatments and loss of fruit quality. Excluding wine exports (NZD 1.7 billion), horticulture is New Zealand’s fourth largest export industry (NZD 2.2 billion, ~6 per cent of total exports), and 80 per cent of our fruit crops are vulnerable to attack. Fruit for processing would also be impacted by production loss and pest management measures.
"For the home gardener keen on their own fruit, there would be the inconvenience and cost of monitoring with traps and increased use of pesticides, bringing additional environmental and health impacts."
How is the Queensland fruit fly able to travel from Australia to an Auckland suburb?
"It is not likely that commercial fruit would be a source. Australian fruit exporters adhere to strict import health standards, and their continued trade with New Zealand is dependent on fruit fly-free fruit.
"Compliance by visitors to New Zealand, on the other hand, depends on how well we get the message out that fruit fly introduced to New Zealand would have serious economic consequences for the country. The major airports are fairly well managed in that regard. But, for example, it is more difficult to monitor visitors arriving on yachts or cruise ships bringing fruit that they may have bought in Australian or Pacific Island markets."
Why have they been most likely to be found in the upper North Island? Are there other regions that are equally at risk?
"Greater number of interceptions in the North Island is likely because of the greater number of people arriving into Auckland from Australia and the Pacific, compared with South Island ports.
"However, the consistently warmer temperature and higher humidity in the North Island will also encourage completion of the flies’ life cycle. So eggs or larvae that arrive in fruit are more likely to reach the adult stage. This is the life stage that our year-round trapping system detects. And, of course, these are also the conditions that suit growth of backyard fruit, which provides convenient and available host material for much of the year.
"Conversely, even if infested fruit is introduced to the South Island, the cooler, dryer conditions of the east coast where the major ports are mean the flies may never emerge. For the same reasons availability of backyard host fruit material is less.
"Climate warming has been predicted to change this, such that the east coast of the South Island would provide more suitable temperatures for the Queensland fruit fly to develop."
What border biosecurity measures are in place, for both international travellers and produce importers, to prevent the fruit fly coming in?
"Information is key. Getting this out to travellers as they enter the country, explaining what to look for and why, and making it easy to mitigate the risk, such as with fruit amnesty bins at the airports, encourage visitors to understand the importance to this country and to comply. But as a backup, fruit detector dogs and X-rays are used for flights and passengers coming from high-risk places such as Queensland and the Pacific.
"Importers of fresh fruit, on the other hand, have a clear and strict import health standard to work with. This includes pre-export inspections and disinfestation treatments, such as keeping the fruit in the cold for a period of time, or low-level irradiation for others such as mangoes. During transit, the produce must be contained in a way that makes it impossible for the fruit to become infested, and once it arrives in New Zealand it’s transported directly to an approved inspection facility for final clearance."
Why is it necessary to place bans on taking fresh fruit and vegetables outside an area where fruit flies have been found?
"Infested fruit are difficult to distinguish from clean fruit until they’re cut or eaten. Therefore moving fruit around increases the risk that adults may emerge in a different place to where the original infestation was introduced.
"This helps the pest spread. But it also makes it harder for authorities to contain and understand the likely distribution of the fly, which is essential for successful eradication.
"The result of not being able to contain fruit to the original area will be geographically wider and longer disruption to the public, small businesses and growers while an eradication programme is in place."
Are there other similar threats to horticulture in New Zealand that biosecurity authorities are on the look-out for?
"Many. Besides the many other damaging fruit flies, such as the Mediterranean and Oriental fruit flies, there is the hitchhiker pest brown marmorated stink bug. This has a large, indiscriminate range of fruit that it feeds on. But in autumn, when they seek shelter to overwinter, they become a severe urban pest, aggregating in the thousands and invading crevices in houses.
"Drosophila suzukii, the spotted wing drosophila, looks like the small fly you find around ripe fruit in your fruit bowl. But this species is unusual in that it attacks ripening fruit before harvest. It attacks a wide range of crops, including grape. Endemic to Asia, it has recently shown a disturbing invasive movement into the temperate regions of the USA and Europe.
"The spotted lanternfly, another species endemic to Asia, is an emerging pest of pip fruit, stone fruit, kiwifruit, and grapes. It has only recently invaded the USA where its numbers have grown rapidly. Also, a hitchhiker that is difficult to detect, it is difficult to control with pesticides.
"The kanzawa spider mite and serpentine leafminer have also been on watch lists for a while with potentially significant economic impacts on New Zealand’s horticultural industry."
No conflicts of interest declared.
Dr David Teulon, Better Border Biosecurity and Plant & Food Research, and Dr John Kean, Better Border Biosecurity and AgResearch.
The Queensland fruit fly has so far been detected five times in the upper North Island in the past decade. Are we likely to see more Queensland fruit flies turning up in New Zealand in the future? Why?
"New Zealand (government and industry) has invested in an extensive fruit fly (including Queensland fruit fly) trapping system in anticipation of continued fruit fly incursions, and to provide assurances to our trading partners of continuing fruit fly freedom.
"It is impossible to eliminate all risk of Queensland fruit fly (QFF) entering NZ without stopping trade and travel (tourism and returning New Zealanders). QFF is present in Australia, French Polynesia and New Caledonia. Increasing trade and tourism to New Zealand mean that the risk of detections or incursions of QFF will remain."
The Queensland fruit fly has been described as one of the biggest threats to New Zealand horticulture. What crops are most at risk from the fruit fly? What’s the worst-case scenario if a population were to establish itself in New Zealand?
"QFF infests a wide range of crops in Australia and is of concern for many horticultural crops in New Zealand (see MPI’s website). The GIA Fruit Fly Council – a NZ government/industry group that aims to reduce the potentially devastating impact of a fruit fly incursion (including QFF) - represents about 12 industry groups.
"A worst-case scenario would be the establishment of a permanent breeding population of QFF in New Zealand. Such a scenario could potentially stop exports of host crops from a given region, depending on the responses from the country where the exports are being sent. Such a situation could also see QFF spoiling the fruit in home gardens. This scenario has not occurred in New Zealand due to our multi-layered biosecurity system of prevention, inspection, surveillance and eradication."
How is the fruit fly able to travel from Australia to an Auckland suburb?
"The principal means by which fruit flies travel long distances is as eggs or larvae inside fruit.
"Potential pathways include trade, tourism, returning NZers, and mail, for which New Zealand has a layered biosecurity system to prevent the establishment of fruit fly in NZ.
"It is highly unlikely that QFF adults can spread to NZ naturally (e.g. by wind from Australia)."
Why have they been most likely to be found in the upper North Island? Are there other regions that are equally at risk?
"For several reasons. The upper North Island is the area of focus for entry of traded goods and international travellers (i.e. the main pathways and points of entry). The climate is also favourable for many fruit flies. MPI and industry recognise the relatively high risk in this area by deploying the greatest concentration of traps for detecting QFF and other fruit flies. The fruit fly trapping system covers all of NZ, with trap numbers proportional to assessed risk."
What border biosecurity measures are in place, for both international travellers and produce importers, to prevent the fruit fly coming in?
"Biosecurity is a multi-layered system with each layer contributing to the reduction in the probability of fruit fly entering New Zealand. There are multiple measures in place to prevent fruit fly arriving through commercial pathways (e.g. pest-free areas of production, pre-export inspection, border inspection etc.). Passenger arrivals are managed via the processes we are familiar with at the airport."
Why is it necessary to place bans on taking fresh fruit and vegetables outside an area where a Queensland fruit fly has been found? What factors go into deciding how long to maintain a ban?
"Fruit flies travel as eggs or larvae inside fruit and these are not always obvious externally. Movement controls help to minimise potential spread of fruit flies if a population might be present. This is a necessary part of any successful eradication programme. These controls are removed when it is clear that no population is present."
Are there other similar threats to horticulture in New Zealand that biosecurity authorities are on the look-out for?
"The biosecurity community (government, industry, researchers) is continually scanning the world (by various means) for information on pests, diseases and weeds that might negatively impact New Zealand agriculture.
"Some of the current pests of concern for NZ horticulture include: brown marmorated stink bug, spotted winged drosophila, spotted lanternfly, and Pierce’s disease (Xylella fastidiosa). But there are potentially many more."
A second fruit fly has been found in Auckland, though it is a different species to the Queensland fruit fly. How worried should the horticulture industry be about the discovery of this second fruit fly?
"We believe that the horticulture industry is worried about any economic fruit fly entering and establishing in NZ. To address this, the Government Industry Agreement Fruit Fly Council has a vision for New Zealand to remain free from economically-significant fruit fly."
Is it possible that there are other potentially damaging exotic species in New Zealand that haven't yet been detected?
"With respect to fruit flies, this seems to be very unlikely. It has not happened before. All previous fruit fly incursions have been located in time for eradication and NZ is considered to be fruit fly free.
"From a broader point of view, it is impossible to keep all pests, diseases and weeds out of NZ without stopping trade and international travel (tourists and returning NZers) and even then some organisms may be blown in by wind. There are a number of occurrences when potentially damaging species have been found in NZ too late for any chance of eradication. Recent data would suggest that the rate of establishment of invasive species is going down relative to the increase in trade and tourism. Nevertheless, given the resources and tools we have in NZ it is important for us to target the high impact species, such as fruit flies, where we have a good chance of success."
Conflicts of interest: Dr David Teulon (Director B3 and Plant & Food Research) and Dr John Kean (Theme Leader B3 and AgResearch) undertake research on invasive species as part of the Better Border Biosecurity (B3) research collaboration which includes research, government and industry parties.
ends
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