Probability of establishment

The likelihood that taro beetles will establish within Australia, based on a comparison of factors in the source and destination areas considered pertinent to their survival and reproduction, is: MODERATE.

• 
  Native populations of taro exist in the Northern Territory. Extensive naturalised populations of taro exist in Queensland, as well as in Western Australia and New South Wales. Taro is considered to be one of the 200 most invasive weeds in South East Queensland (Batianoff and Butler 2002).
  
• 
  The climatic conditions in some parts of northern Australia are similar to the conditions in parts of the Pacific where taro beetles are found, such as Papua New Guinea.
  
• 
  Taro beetles (Papuana spp.) have been recorded in Australia several times over the past century, but only Papuana woodlarkiana is considered to be present (Cassis et al. 1992; Brooks 1965). No other taro beetles have become established or spread, despite the presence of numerous hosts including Colocasia esculenta, a favourable climate, the use of various aroids as foliage plants in horticulture, and a taro industry that has existed in some form since the 1850s.
  
• 
  Adult male beetles are the most likely stage to be present in the corms (SPC 2003) but would not establish a population.
  

The likelihood that taro beetles will spread within Australia, based on a comparison of those factors in source and destination areas considered pertinent to the expansion of the geographic distribution of these pests, is: HIGH.

• 
  The experience in the Pacific shows that taro beetles will spread and become a serious pest once established in tropical areas. Thus, if the beetles became established in a commercial taro growing area in Australia and remained uncontrolled, they could spread.
  
• 
  Taro beetle larvae require a damp humic soil environment (e.g. the base of sugarcane clumps, banana plants, compost, sawdust piles or moist taro fields). Adult beetles require taro corms or similar soft trunks to complete their lifecycle. Both types of habitat are readily available in close proximity in northern Australia.
  

The likelihood that taro beetles will be imported as a result of trade in fresh taro corms from any country where this pest is present, be distributed in a viable state to a susceptible host, establish and spread within Australia, is: VERY LOW.

Assessment of the potential consequences (direct and indirect) of taro beetles for Australia is: MODERATE.

The unrestricted risk for taro beetles is: VERY LOW.

Unrestricted risk is the result of combining the probability of entry, establishment and spread with the outcome of overall consequences. Probabilities and consequences are combined using the risk estimation matrix shown in Table 2.5.

The unrestricted risk estimate for the taro beetles of ‘very low’ achieves Australia’s ALOP. Therefore, specific risk management measures are not required for these pests.

Taro planthoppers are pests of cultivated taro, directly damaging the plants through their feeding, as well as indirectly by vectoring viruses causing plant diseases such as alomae and bobone (Vargo 2000; Carmichael et al. 2008). The three recognised species of taro planthopper present in Asia and the Pacific are Tarophagus colocasiae, Tarophagus persephone and Tarophagus proserpina (Matthews 2003). Tarophagus colocasiae and Tarophagus persephone have been recorded in Australia (Matthews 2003).

The life history of Tarophagus proserpina occurs above ground, mostly on taro leaves (Matthews 2003). Eggs are laid in pairs in small holes made by the female in the petioles, petiole bases and the midribs of the leaves (Vargo 2000). There are five nymphal stages, lasting around 19 days depending on weather conditions (Vargo 2000). The young nymphs are creamy white, with black and white marking developing in the final stages (Matthews 2003; Carmichael et al. 2008). The adults are 3–4 mm in length, and black with broad white patches on the back of the thorax and abdomen (Carmichael et al. 2008). Like other Delphacidae planthoppers, for most of the year adult taro planthoppers have only short wings and cannot fly, but long-winged forms are often present during cooler periods, or when the taro host plants mature and die. The long-winged forms of Delphacidae can fly long distances. The rice brown planthopper, Nilaparvata lugens, has been reported flying more than 500 km (Matthews 2003).

Taro planthoppers predominantly feed on taro, although they have been observed on Alocasia spp. and Cyrtosperma spp. (Carmichael et al. 2008). The related Tarophagus persephone has also been collected on the weedy plants Mimosa pigra and Sida cordifolia in Australia, although these are not considered likely to be primary host plants (Matthews 2003). Adult and nymphal planthoppers usually congregate on the underside of the taro leaves, feeding on the sap. Reddish crusts form on the leaf surface where the sap oozes out (Vargo 2000). Heavy infestations can cause the leaves to wilt and turn yellow and, in exceptional cases, cause the plant to die (Carmichael et al. 2008).

The likelihood that Tarophagus proserpina will arrive in Australia with the importation of fresh taro corms from any country where this pest is present is: HIGH.

• 
  Taro planthopper adults, nymphs and eggs are associated with the above ground parts of the taro plant, including the petioles and petiole bases (Matthews 2003).
  
• 
  Untopped taro corms with the petiole bases and small tuft of petioles intact could harbour adults, nymphs and eggs.
  
• 
  Taro planthoppers can survive long journeys as unhatched eggs or juvenile forms inside or on their host (Matthews 2003).
  
• 
  The importation of taro planting materials was likely to be responsible for the introduction of Tarophagus proserpina into Polynesia (Matthews 2003).
  
• 
  The female taro planthopper makes small holes in the leaf midrib, petioles or petiole bases into which two eggs are laid. The eggs would be difficult to detect. They hatch after 14 days (Vargo 2000), so it is possible that corms could arrive with eggs in the petioles. However, the outer petiole sheaths, which are most likely to have oviposition punctures, are typically removed during pre-export processing, thereby removing most eggs.
  
• 
  Young nymphs are minute, almost clear and difficult to see (Carmichael et al. 2008) and could be present feeding amongst the petioles.
  
• 
  Both adult and nymphal planthoppers are active and hop readily if they are disturbed (Vargo 2000). They feed on sap on the undersides of taro leaves, or on young unfurling leaves emerging from the petioles (Vargo 2000). The leaves are removed from the corm at harvest. Most adult and nymphal planthoppers will be disturbed during harvest and processing prior to export and hop from the corm, but some may remain amongst the petioles.
  
• 
  Tarophagus proserpina is one of the most commonly intercepted pests on topped taro corms imported from Fiji (AQIS interception data).
  

The likelihood that Tarophagus proserpina will be distributed within Australia in a viable state to a susceptible part of a host, as a result of the processing, sale or disposal of fresh taro corms from any country where this pest is present, is: HIGH.

• 
  The eggs of the planthopper hatch after 14 days (Vargo 2000), so any eggs laid in the petioles or petiole bases in the days before the corms are harvested are likely to remain undetected and subsequently hatch some time after arrival in Australia.
  
• 
  The movement of Tarophagus proserpina into Polynesia may be largely due to transport on planting materials, followed by establishment in taro gardens (Matthews 2003).
  
• 
  Some adults and nymphs may remain concealed amongst the petioles.
  

• 
  Corms will be distributed to many localities by wholesale and retail trade and by individual consumers.
  
• 
  Individual consumers could carry small quantities of taro corms to urban, rural and natural localities. Small amounts of corm waste could be discarded in these localities.
  
• 
  Some corms will be distributed to areas where taro or other aroid species grow.
  
• 
  Small amounts of corm waste will be discarded into domestic compost.
  

• 
  Infested corms that escaped detection during processing and entry are likely to be distributed in the wholesale and retail supply chain.
  

The likelihood that Tarophagus proserpina will enter Australia and be distributed in a viable state to a susceptible host, as a result of trade in fresh taro corms from any country where this pest is present, is: HIGH.

The likelihood that Tarophagus proserpina will establish within Australia, based on a comparison of factors in the source and destination areas considered pertinent to its survival and reproduction, is: HIGH.

• 
  Eggs laid in the petiole bases are a major source of infestation since propagation is by means of corm tops with petiole bases (Matthews 2003). Imported corms with intact petiole bases could be diverted from consumption purposes to be used as planting material, significantly increasing the risk of establishment.
  
• 
  Taro planthoppers are typically host-specific to taro, but are occasionally associated with other related plants such as Alocasia spp. and Cyrtosperma spp. (Carmichael et al. 2008). A number of species of these genera are common in many parts of Australia.
  
• 
  Other taro planthopper species have established in wild taro populations in Queensland, typically around lowland swamps and watercourses. As the commercial cultivation of taro in Australia has been relatively limited up until recently, these planthopper populations in wild taro may pre-date the modern introduction of taro cultivars (Matthews 2003).
  
• 
  The entire lifecycle takes place on the above ground parts of the taro plant. If the infestation is severe enough to kill the host plant, adults may seek out new hosts in which to oviposit.
  
• 
  Cyrtorhinus fulvus, the mirid predator of taro planthoppers that regulates the pest population in much of the Pacific region (Fatuesi and Vargo 1995), is absent from Australia. Information on Australian mirid species that may potentially feed on Tarophagus proserpina is not available.
  

The likelihood that Tarophagus proserpina will spread within Australia, based on a comparison of those factors in the source and destination areas considered pertinent to the expansion of the geographic distribution of this pest, is: MODERATE.

• 
  Climatic conditions in parts of northern Australia are similar to conditions in the Pacific countries where the planthopper is found.
  
• 
  Tarophagus spp. have been associated with wild taro as well as cultivated taro (Matthews 2003). Host plants are widely available in many parts of Australia. Some spread could be anticipated if it became established.
  
• 
  Adult planthoppers are capable of long distance migration under certain conditions, usually during cooler periods or when healthy host plants become scarce.
  
• 
  Tarophagus spp. have extended beyond their natural range to the islands of Polynesia, Micronesia, Fiji, Vanuatu and Samoa where taro is an introduced crop (Matthews 2003).
  
• 
  Two other species of taro planthopper are already present in northern Australia. These have not spread to southern Queensland or New South Wales, even though suitable hosts are widespread and common.
  

The likelihood that Tarophagus proserpina will be imported as a result of trade in fresh taro corms from any country where this pest is present, be distributed in a viable state to a susceptible host, establish and spread within Australia, is: MODERATE.

Assessment of the potential consequences (direct and indirect) of Tarophagus proserpina for Australia is: LOW.

The unrestricted risk of Tarophagus proserpina is: LOW.

Unrestricted risk is the result of combining the probability of entry, establishment and spread with the outcome of overall consequences. Probabilities and consequences are combined using the risk estimation matrix shown in Table 2.5.

The unrestricted risk estimate for Tarophagus proserpina of ‘low’ exceeds Australia’s ALOP. Therefore, specific risk management measures are required for this pest.

1.10Paraputo mealybugs

Paraputo aracearum; Paraputo leveri

Paraputo is a genus of about 80–85 species of mealybugs of the New World, south Asia, China and the Pacific (Williams 2005; Ben-Dov et al. 2011). Only two species from the Pacific have been reported to be associated with taro. They are attended by ants, which milk them for honeydew, but very little is known of their lifecycles or epidemiology. Paraputo aracearum is known to feed exclusively on taro plants. Paraputo leveri is only a minor pest of taro, and is mostly associated with tree roots.

These two mealybugs have been grouped together in this pest risk assessment because of their similar biology (Williams 2005). Their lifecycle and behaviour are not well described, particularly for Paraputo aracearum, which so far has only been found in Fiji (Williams 2005). Paraputo leveri has a broader host range and geographical distribution.

The likelihood that Paraputo spp. will arrive in Australia with the importation of fresh taro corms from any country where these pests are present is: MODERATE.

• 
  Paraputo spp. of concern are distributed in South East Asia and the Pacific region.
  
• 
  Paraputo aracearum is only recorded from Fiji (Williams 2005). It has been intercepted twice in California (in 1994 and 1996) on taro corms entering the USA from Fiji (Williams 2005).
  
• 
  Paraputo leveri has been reported on taro in Papua New Guinea and Solomon Islands (Ecoport 2011). However, it is mainly found in association with tree roots, particularly coconut (Cocos nucifera) and coffee (Coffea spp.), on stems of bishopwood (Bischofia javanica), and on Tahitian chestnut (Inocarpus edulis), Balanophora sp. and Ficus sp. (Williams 2005).
  
• 
  Paraputo leveri is often found on roots and may be carried on plant material (Williams 2005).
  
• 
  Paraputo leveri has been intercepted on taro entering Hawaii from Western Samoa (Williams 2005).
  
• 
  Mealybugs would mostly feed on the smaller roots, rather than the corm. These roots are removed from the corm before export.
  

The likelihood that Paraputo spp. will be distributed within Australia in a viable state to a susceptible part of a host, as a result of the processing, sale or disposal of fresh taro corms from any country where these pests are present, is: MODERATE.

• 
  Mealybugs that escape detection at the border are likely to remain attached to the corms and be distributed via the wholesale and retail supply chain. They are unlikely to be treated or destroyed in the retail supply chain unless the infestation is conspicuous.
  

• 
  Corms will be distributed to many localities by wholesale and retail trade and by individual consumers.
  
• 
  Individual consumers will carry small quantities of taro corms to urban, rural and natural localities. Small amounts of corm waste could be discarded in these localities.
  
• 
  Some corms could be distributed to areas where taro or other aroid species grow.
  
• 
  Small amounts of corm waste will be discarded into domestic compost.
  

• 
  Some corms of small corm taro may be planted for domestic cultivation instead of being consumed.
  

The likelihood that Paraputo spp. will enter Australia and be distributed in a viable state to a susceptible host, as a result of trade in fresh taro corms from any country where these pests are present, is: LOW.