Final Import Risk Analysis Report for Fresh Mango Fruit from India

4.4 Fruit flies [Diptera: Tephritidae] – mangoes as a preferred host

Fruit flies are of concern because their larvae generally complete their feeding and development within the host fruit (Fletcher 1989a). Fruit with infestation normally show obvious signs of attack or tissue decay. However, infested fruit cannot always be distinguished from uninfested fruit (White and Elson-Harris 1992). The transportation of infested fruit is regarded as the major means of movement and dispersal of fruit flies (Baker et al. 2000; Iwaizumi 2004) and therefore deserves the most scrutiny in terms of pathways for introduction.

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  Bactrocera caryeae
  
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  Bactrocera correcta – guava fruit fly
  
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  Bactrocera dorsalis – Oriental fruit fly ^EP
  
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  Bactrocera invadens – Asian fruit fly
  
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  Bactrocera zonata – peach fruit fly
  

4.4.1 Probability of entry

Probability of importation

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  Bactrocera caryeae, B. correcta, B. invadens and B. zonata have been reported on mangoes in India (Peña et al. 1998; Kumar and Bhatt 2002; Drew and Raghu 2002; Hanna 2005).
  
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  In the mango production regions of India, adults of B. correcta and B. zonata occur throughout the year and abundance increases during mango ripening and harvest (Srivastava 1997; Peña et al. 1998). Up to 100% of fruit can be infested in unmanaged orchards (Stonehouse et al. 1998).
  
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  Bulleted, Wingdings (symbol), Left: 0 cm, Hanging: 4.2 chFruit fly larvae can survive in harvested fruit and may be present in fruits that are packed for export. As fruit fly eggs are laid internally, infested fruit may not be detected during sorting, packing and inspection procedures. Inspection procedures carried out in the packing houses are concerned primarily with quality standards of fruit with regard to blemishes, bruising or damage to the skin.
  

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  The optimum temperature for storage of mangoes is approximately 13-14^oC, as storage below this temperature results in chilling injury to the fruit (Lederman et al. 1997; Nair and Singh 2004). At low temperatures, development times for fruit flies are extended significantly and mortality increases for all life stages (Duyck et al. 2004). Although development thresholds have not been reported for all species considered here, Duyck et al. (2004) reported that the lower development thresholds for B. zonata eggs, larvae and pupae are 12.7, 12.6 and 12.8°C respectively. Mohamed (2000, as cited in Duyck et al. 2004) calculated lower temperature thresholds of 10, 10 and 11.8°C for the egg, larval and pupal stages of B. zonata respectively. Therefore, immature stages could continue to develop at the optimum storage temperature of 13-14^oC.
  
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  Bactrocera caryeae has been intercepted on mango from India in Japan (Iwaizumi 2004). Bactrocera correcta has been detected during surveillance in California and Florida in the USA (Weems 1987, Weems 2001). In commercial consignments of mango, B. zonata has been intercepted from Pakistan and B. invadens from Senegal in the United Kingdom (DEFRA 2008). This further supports that Bactrocera species can survive transport and storage and could be imported into Australia via the movement of fruit.
  

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  Bactrocera species are typically managed in India by trapping, bait sprays and collection and deep burial of fallen fruit (DAC 2007). These methods will reduce but not necessarily eliminate populations.
  

Probability of distribution

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  Fruit fly eggs or larvae infested fruit arriving in Australia would still need to develop into mature larvae and pupate. Fruit flies develop quickly, with a wide host range and excellent dispersal capabilities (Fletcher 1989a, 1989b).
  
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  Mango fruit from India would be imported during the winter months in Australia. At this time, the coastal regions of Australia north of Sydney may have suitable temperatures to allow the slow development of larvae and pupae (Duyck et al. 2004).
  
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  Most Bactrocera species have a wide host range including horticultural crops and ornamentals (Srivastava 1997; Allwood et al. 1999), and these hosts are widely distributed throughout Australia.
  
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  Fruit flies might enter the environment through:
  

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  eggs developing into larvae within stored fruit, fruit at the point of sale, or fruit that has been purchased. Larvae may then develop into adult flies which are able to move directly into the environment.
  
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  wholesalers, retailers or consumers discarding fruit with spoiled flesh or visible larvae. Infested fruit typically contains several larvae (Kumar and Bhatt 2002) which can complete larval development in discarded fruit, pupate in soil and adults can then transfer to suitable hosts (Fletcher 1987).
  

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  Mangoes would be distributed for sale to multiple destinations in Australia.
  
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  Eggs may develop into larvae within fruit throughout the distribution chain. Wholesalers, retailers or consumers could discard spoiled fruit containing eggs or larvae at multiple locations.
  

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  The intended use of the commodity is human consumption but waste material would be generated. Larvae could complete development in waste material.
  
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  Newly emerged adults contain some energy reserves carried over from the larval stage, which enables them to survive for 1–2 days post-emergence if food is not available (Fletcher 1987).
  
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  Larvae develop into adult flies and are able to move directly from fruit into the environment to find a suitable host. Adult flies typically live for periods of months (Christenson and Foote 1960; Fletcher 1989b).
  

Probability of entry (importation x distribution)

4.4.2 Probability of establishment

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  These fruit flies are capable of surviving and reproducing on a wide host range, including citrus, mango, peach and several other subtropical fruits (White and Elson-Harris 1992; Allwood et al. 1999; Hanna 2005). These host species are widespread in cities, towns and horticultural production areas throughout Australia.
  
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  Bactrocera correcta has the potential to become a pest of citrus and peach, as well as several other subtropical fruits (Weems 1987; Allwood et al. 1999). Bactrocera invadens
  

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  The survival of these fruit flies in a wide range of climates suggests that regions of Australia are likely to be suitable for the establishment of these species (Espenshade 1990; Gomes 2000; Hanna 2005). Bactrocera species occur throughout the Indian subcontinent (White and Elson-Harris 1992), across climatic zones that are similar to areas in Australia (Espenshade 1990).
  
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  Bactrocera caryeae is distributed in the tropical climatic zone of southern India, and is active at higher altitudes (Allwood and Drew 1997). Bactrocera zonata is a tropical species endemic to India (Drew and Raghu 2002). Each has the potential to establish itself in similar environments in Australia.
  
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  Originally considered to be an exclusively tropical fruit fly, the establishment of B. zonata in Egypt in 2001 demonstrates that B. zonata can also thrive in a Mediterranean climate (Duyck et al. 2004). The B. zonata population in Egypt has demonstrated adaptation in a relatively short time frame (Iwahashi and Routhier 2001), proving its ability to establish and successfully compete in new environments.
  
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  Bactrocera invadens has expanded its distribution from the Indian-subcontinent to tropical Africa (Hanna 2005).
  

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  As these fruit flies are internal pests of fruit, current insecticide spray regimes may not have any impact on their establishment in Australia.
  
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  Integrated pest management programs have been adopted for other fruit flies, including monitoring the emergence and dispersal of adults, using baits, male annihilation and sterile insect techniques (Kuba et al. 1996; CAB International 2007).
  
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  Trapping systems are routinely used in commercial orchards to detect fruit flies (Dominiak 2007). Currently, trapping measures are used in Australia implemented to effectively detect Bactrocera species in Australia.
  

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  Adults of Bactrocera species typically live for several months depending on the species and temperature, for example B. dorsalis can live up to 12 months in cool conditions (Christenson and Foote 1960; Gomes 2000; Dhillon et al. 2005).
  
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  Bactrocera species prefer warm, humid weather and abundance increases as mangoes ripen but the population declines during dry periods (Peña et al. 1998).
  
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  For most Bactrocera species, it is the adults that are best able to survive low temperatures, with a nominal torpor threshold of 7°C, dropping as low as 2°C in winter (OEPP/EPPO 2005). Bactrocera zonata overwinters in the larval or pupal stage (Gomes 2000; OEPP/EPPO 2005) and mating begins after the adults emerge, when the ambient temperature increases.
  
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  The average life span of the adult in the field will normally depend on the existence and presence of natural enemies, on the nature and abundance of available food and on climatic conditions (Gomes 2000).
  
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  The wide host ranges allow these fruit flies to breed actively in the field from the end of winter through to autumn and produce several generations per year. The life cycle is completed in 20 days under optimum conditions but is prolonged by cool temperatures (Gomes 2000).
  

4.4.3. Probability of spread

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  These fruit flies have been reported from a variety of environments. For example Bactrocera correcta and B. zonata are widespread in the tropics (Gomes 2000; Weems 2001) and B. zonata has recently established in the Mediterranean climate of Egypt (Duyck et al. 2004). Bactrocera invadens has established in humid lowland regions of Africa (Hanna 2005). There are similarities in the natural and managed environments of these regions with many of those in Australia.
  
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  These species have a broad host range (Allwood et al. 1999), and the hosts are readily available in Australia.
  
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  The incursion of B. papayae in northern Australia in 1995 demonstrates the ability of introduced fruit fly species to spread. The fruit fly was detected near Cairns and the infested area was found to extend from Kennedy in the south to as far north as Cooktown, with the largest infestations around Mareeba and Cairns. The declared pest quarantine area included 78,000 km² of north Queensland, including urban areas, farms, riparian habitats, coastline and a large part of the Wet Tropics World Heritage Area before it was finally declared eradicated in 1999 (Cantrell et al. 2002). Bactrocera correcta and B. zonata would have a similar capacity to spread in Australia.
  

The presence of natural barriers such as deserts or mountain ranges may inhibit long-range natural spread of these fruit flies. The long distances between commercial host crops in Australia may reduce the potential for long-range natural spread of fruit flies.

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  Bactrocera species adults engage in extensive dispersive movements during the early adult phase prior to host-seeking and mating, and mature flies leave locations where hosts are dwindling in search of new hosts. During these periods, some individuals may move large distances in a few weeks. A dispersal distance of 25 km has been recorded for B. zonata (Gomes 2000). Should these fruit flies be introduced to major commercial production areas of Australia they are capable of short distance spread unaided.
  
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  Bactrocera zonata tends to remain in one area when adequate food and hosts are available (Gomes 2000).
  

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  The major means of dispersal to previously unaffected areas is transport of infested fruits (Baker et al. 2000). Adults and immature forms may spread undetected by this means.
  
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  There are restrictions in place in Australia on the movement of fruit to prevent the spread of fruit flies, including Mediterranean fruit fly, Queensland fruit fly and exotic species.
  
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  Following the incursion of B. papayae in northern Australia in 1995, fruit fly traps for exotic Bactrocera species are now located in Australia at each first port of call to attract and trap these fruit flies. These traps may limit the spread of these species by providing early warning of their presence that would lead to their successful eradication, as occurred with B. philippinensis in Darwin in 1999.
  

4.4.4 Overall probability of entry, establishment and spread

The overall probability that fruit flies will be imported as a result of trade in mango fruit from India, be distributed in a viable state to a susceptible host, establish and spread within Australia, is: HIGH.

4.4.5 Consequences

4.4.6. Unrestricted risk estimate