Final Import Risk Analysis Report for Fresh Mango Fruit from India

4.5. Fruit flies [Diptera: Tephritidae] – mangoes as a non–preferred host

4.5.1. Previous policy: Melon fruit fly – Bactrocera cucurbitae [Diptera: Tephritidae]

Melon fruit fly has previously been assessed for the importation of mango from Taiwan with an unrestricted risk rating of ‘low’. The existing policy for Melon fruit fly is adopted for the importation of mango from India as the risks of importation and distribution are judged to be similar. Therefore, melon fruit fly is not considered further in this policy.

4.5.2. Previous policy: Pumpkin fruit fly – Bactrocera tau [Diptera: Tephritidae]

Pumpkin fruit fly has previously been assessed for the importation of mango from Taiwan with an unrestricted risk rating of ‘very low’. The existing policy for Pumpkin fruit fly is adopted for the importation of mango from India as the risks of importation and distribution are judged to be similar. Therefore, Pumpkin fruit fly is not considered further in this policy.

4.6. Armoured scales [Hemiptera: Diaspididae]

The crawlers wander around finding a suitable place to settle. Once settled, they secrete a scale cover by producing waxy filaments that are laid down in a circular fashion by rotation of the body. The male scale is smaller and more oblong than the female and at the final moult produces a tiny winged male that slips out from beneath the scale and flies off to find a female that needs mating.

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  Abgrallaspis cyanophylli – Cyanophyllum scale^EP
  
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  Parlatoria crypta – mango white scale
  

4.6.1. Probability of entry

Probability of importation

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  Mango white scale has been reported in India on mangoes (Ben-Dov et al. 2006).
  
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  Armoured scales are quite small and may be difficult to detect, particularly in low numbers. Female adults of mango white scale are approximately 1.25 mm long and 1 mm wide (Ben-Dov et al. 2006).
  
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  First instar nymphs (or crawlers) are capable of movement onto fruit where they permanently attach and commence feeding (Beardsley and Gonzalez 1975). Subsequent instars are sessile (Watson 2007). The normal post-harvest practice of washing fruit to remove sap (Morton 1987) may remove some mango white scale on the fruit at the time of harvest, but the effective removal of all scales may be difficult (Taverner and Bailey 1995).
  
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  The detection of mango white scale on Pakistani mangoes on arrival in the United Kingdom (DEFRA 2008) demonstrates that post-harvest cleaning and washing will not remove all scales and quality control inspectors within the packing house may miss some infested fruit.
  

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  As the development of armoured scales is strongly dependant on temperature (Beardsley and Gonzalez 1975), the development of nymphs would be slowed or halted by cool storage. However attached adults and nymphs can remain viable during transport and storage as the fruit would provide an ample supply of food during transit.
  

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  Armoured scale species can be controlled with the use of insecticides that hinder the normal formation of the protective scale cover (Foldi 1990).
  
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  Crawlers are mobile, with the ability to disperse and settle on twigs, leaves, fruit and the bark of tree trunks (Timmer and Duncan 1999). Once settled, the crawlers penetrate the plant with their piercing stylets and feed on the juices. Females become sessile for the remaining nymphal instars (Carver et al. 1991). It is likely that fruit sent to be packed for export will contain some of these pests, as field control does not provide complete control of scales (Taverner and Bailey 1995).
  
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  Mango white scale has been intercepted on mango fruit, showing that armoured scales can survive existing pest management procedures.
  

Probability of distribution

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  The stages associated with imported fruit would be immature forms or adults. However, during developmental stages scale insects are firmly attached to their host and are usually incapable of independent movement (Carver et al. 1991).
  
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  Either mated female scales would need to arrive in Australia with mango fruit, or male scales would need to complete development, emerge and locate a female for mating, before eggs could be laid.
  
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  There are two principal means by which armoured scales may transfer to a suitable host: active dispersal of crawlers and the action of wind (Beardsley and Gonzalez 1975). Birds, insects and other animals, including humans, may also act as vectors.
  
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  Emerging crawlers (first instars) would need to locate a suitable host to infest. While crawlers are capable of independent movement, and can be moved by wind (Carver et al. 1991), they generally move for a limited period of time and do not move far before settling to feed (Ker and Walker 1990). Abiotic factors such as unsuitable temperatures strongly influence the survival rate for crawlers during the dispersal stage (Watson 2007).
  
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  Although, crawlers may travel up to 150 m, they usually settle within several dozen centimetres of their hatching site (Koteja 1990).
  
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  Mango white scale has a wide host range (Ben-Dov et al. 2006). Thus there is a good chance of a suitable host being available in Australia.
  

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  Mangoes would be distributed for sale to multiple destinations in Australia.
  
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  Wholesalers, retailers or consumers could discard infested fruit at multiple locations. Mango will presumably be shipped all over Australia, so a portion of the pests that enter the country are likely to reach areas of host abundance.
  

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  The intended use of the commodity is human consumption, but waste material will be generated. Immature stages could complete development on discarded waste.
  
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  The nymphal stages associated with imported fruit waste may develop into adults. However, adult female scales are firmly attached to their host and are usually incapable of independent movement (Carver et al. 1991).
  
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  The principal dispersive stage of scale insects is the first instar crawlers (Carver et al. 1991). Adult males, while capable of independent flight are incapable of laying eggs and thus would not be able to move the scale infestation onto a new host.
  

Probability of entry (importation x distribution)

4.6.2. Probability of establishment

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  Parlatoria crypta is capable of surviving and reproducing on a wide potential host range (Ben-Dov et al. 2006). Host species include horticultural crops and ornamentals that are widespread in cities, towns and horticultural production areas in Australia.
  
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  Armoured scales can be highly polyphagous (Beardsley and Gonzalez 1975), with many potential host species present in Australia.
  

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  Armoured scales are distributed in a wide range of climates (Ben-Dov et al. 2006; Watson 2007), and regions of Australia are likely to be suitable for the establishment of these species (Espenshade 1990).
  
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  Climatic conditions, particularly temperature, humidity and rainfall strongly influence the development of armoured scales (Beardsley and Gonzalez 1975). Temperature influences both the initiation and rate of crawling, as well as crawler survival. The threshold for crawler activity appears to be between 13°C and 20°C (Beardsley and Gonzalez 1975). Therefore most of Australia would be suitable. Low humidity and extreme temperatures limit the establishment and spread of Diaspididae species (Beardsley and Gonzalez 1975).
  

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  Scales are external feeders and existing pest management practices such as pesticide application may impact the establishment of scales in Australia. Scales are often controlled by predators such as small parasitic wasps and beetles (Dreistadt et al. 1994).
  
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  Chemical controls in commercial orchards may impact on the establishment of these scales, but would not be applied in all the environments where these scales could establish, particularly in urban environments. Broad spectrum insecticides applied to control scales and other arthropods may also reduce population numbers of natural enemies of armoured scales (Dreistadt et al. 1994).
  

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  Reproduction in Diaspididae species is bisexual (Beardsley and Gonzalez 1975), so a mating pair is not needed.
  
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  No specific information is available on the biology of mango white scale, but related species have many generations per year and produce high numbers of offspring. For instance, P. pergandii populations in Queensland, Australia, produce five to six generations per year (Smith et al. 1997).
  
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  The survival of Diaspididae species is strongly influenced by relative humidity and temperature (Beardsley and Gonzalez 1975). They cannot survive well under low relative humidity and high temperatures. Several species of Parlatoria are already established in Australia, suggesting that mango white scale may also be able to establish.
  
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  Adult males are short-lived, winged and capable of weak flight. They lack functional mouthparts and cannot feed. This stage generally lives for only a few hours (Beardsley and Gonzales 1975).
  

4.6.3. Probability of spread

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  Parlatoria species have been reported from a variety of environments. For example mango white scale is present in parts of Asia and Africa (Ben-Dov et al. 2006). There are similarities in the natural and built environments of these areas with those in Australia.
  
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  Mango white scale has a broad host range (Ben-Dov et al. 2006) and many of these hosts occur in Australia.
  
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  The spread of Parlatoria species depends on relative humidity and temperature (Beardsley and Gonzalez 1975). The number of days for each developmental stage and the number of generations per year depend on temperature, humidity and rainfall (Beardsley and Gonzalez 1975). They cannot spread and establish well under low relative humidity and high temperatures.
  

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  The presence of natural geographical barriers such as deserts or mountain ranges will prevent long-range natural spread of these armoured scales.
  
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  Crawlers are the primary dispersal stage and move to new areas of the plant or are dispersed locally by wind or animal contact. Mortality due to abiotic factors is high in this stage (Beardsley and Gonzales 1975). Dispersal (particularly long distance dispersal) of sessile adults and eggs occurs almost entirely through human transport of infested plant material.
  
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  If mango white scale is introduced to major commercial production areas of Australia the monoculture will favour slow natural local spread.
  

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  Movement of infested planting material or produce is the main way by which armoured scales have been introduced to other countries (Beardsley and Gonzalez 1975).
  
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  Adults and nymphs may be spread through agricultural practices (Dreistadt et al. 1994), including movement of plant material, equipment, and personnel within and between orchards or other commercial production sites.
  
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  The most common mode of dispersal of sessile stages is on plant parts transported by human activities (Beardsley and Gonzalez 1975; Watson 2007). In particular, long-range dispersal of the sessile female scale can only occur by transport of infested plant material. Passing animals or people can also vector crawlers over great distances (Beardsley and Gonzalez 1975; Watson 2007).
  
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  Short-range dispersal may occur through the movement of crawlers in wind currents or by biological or mechanical vectors (Willard 1974).
  

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  Several natural enemies that attack scales occur in Australia. Aphytis wasps parasitise the eggs, nymphs and adults of Parlatoria species and the chilocorus ladybird (Chilocorus circumdatus) is a common predator of armoured scales (Smith et al. 1997). The wide distribution of some Parlatoria species in Australia suggests that these parasites are unlikely to be effective in preventing establishment and spread of mango white scale.
  

4.6.4. Overall probability of entry, establishment and spread

The overall probability that mango white scale 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: LOW.

4.6.5. Consequences

4.6.6. Unrestricted risk estimate