The unrestricted risk for Howardia biclavis, Ischnaspis longirostris, Lepidosaphes pinnaeformis, Lopholeucaspis japonica, Parlatoria theae, Pseudaonidia duplexand Unaspis euonymi 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 armoured scales of ‘very low’ achieves Australia's ALOP. Therefore, specific risk management measures are not required for these pests.
Mealybugs are sucking insects that injure plants by sucking sap and producing honeydew, which serves as a substrate for the development of sooty moulds. The sooty mould prevents photosynthesis in addition to making the plant, including the fruit, unsightly. Many mealybug species pose serious problems to agriculture, particularly when introduced into new areas of the world where their natural enemies are not present (Miller et al. 2002).
The pathway for entry of mealybugs is that eggs, juveniles or adult females may be present in sheltered areas, such as the calyx or the stem end, of imported fruit.
The mealybugs considered in this import risk assessment are Planococcus kraunhiae, Planococcus lilacinus, Pseudococcus comstocki and Pseudococcus cryptus. These species have been grouped together because of their related biology and taxonomy. In this assessment, the term ‘mealybugs’ is used to refer to these species, unless otherwise specified.
Probability of entry
Probability of importation
The likelihood that mealybugs will arrive in Australia with the importation of fresh unshu mandarin fruit from the production area in Japan is: HIGH.
Mealybugs generally live around the calyx of the fruit from flowering onwards. They generally remain anchored to the host, and due to their small size (0.5–4 mm) may be difficult to detect on fruit during sorting, especially at low population levels (Taverner and Bailey 1995).
Mealybugs have a protective coating and routine packing house procedures (washing and grading) may not remove all mealybugs from the fruit. Although mealybugs may be affected by the washing, they are not destroyed by it. This is particularly true of those adult females and/or nymphs that have found protective spaces around the calyx or are protected by waxy cocoons.
The association of mealybugs with fruit, their inconspicuousness and protective coating to withstand packing house procedures all support a risk rating for importation of ‘High’.
Probability of distribution
The likelihood that mealybugswill be distributed within Australia in a viable state, as a result of the processing, sale or disposal of fresh unshu mandarin fruit from the production area in Japan is: MODERATE.
The pests are likely to survive storage and transportation, as mealybugs are capable of hibernation during cold periods (Smith et al. 1997). Fresh unshu mandarin fruit exported to New Zealand and the USA is shipped from Japan in refrigerated containers maintained at 4ºC to 6ºC for about 2 to 4 weeks (refer to Chapter 3). Pseudococcus cryptus is able to survive for up to 42 days when stored at 0°C (Hoy and Whiting 1997). The distributional range of Ps. comstocki and Pl. kraunhiae includes temperate climatic zones (CAB International 2007). Therefore, these species are likely to survive the temperatures during transportation to Australia.
Unshu mandarin fruit is intended for human consumption. Adults and immature stages may remain on fruit during distribution. Peel is unlikely to be consumed, and its disposal as waste may aid dispersal of viable mealybugs.
Disposal of infested fruit or peel into the environment provides the potential for these pests to transfer to susceptible hosts in the vicinity. All nymphal and adult stages can walk. Male mealybugs are winged at emergence and can fly, though their wings are fragile. Males only live for a short time (2–7 days) (Mau and Kessing 2000).
Crawlers are the primary dispersal phase in mealybugs’ life-cycle (Ben-Dov 1994). The lack of active (by flight) long distance dispersal mechanisms of most mealybug life stages may moderate the rate of distribution of these species.
The ability of mealybugs to survive cold periods by hibernation, their potential to remain associated with fruit peel and their lack of an active dispersal mechanism for most of their life stages all support a risk rating for distribution of ‘Moderate’.
Probability of entry (importation distribution)
The likelihood that mealybugs will enter Australia and be transferred in a viable state to a susceptible host, as a result of trade in fresh unshu mandarin fruit from the production area in Japan, is: MODERATE.
The likelihood that mealybugswill establish within Australia, based on a comparison of factors in the source and destination areas considered pertinent to their survival and reproduction, is: HIGH.
Many mealybugs, including the four species assessed, are considered invasive and have been introduced into new areas and become established (Miller et al. 2002). These mealybug species have shown that they have the ability to establish after being introduced into new environments. For example Pl. lilacinus is native to the Afrotropical region (Miller et al. 2002) and is now established in the Palaearctic, Malaysian, Oriental, Australasian and Neotropical regions (CAB International 2007). Similarly, the distributional ranges of Pl. kraunhiae and Ps. comstocki, which originate in Asia, have expanded into North America and Europe. Pseudococcus cryptus is spreading in Asia (CAB International 2007) and is particularly a pest of citrus in Israel, into which it was introduced in 1937 (Ben-Dov et al. 2005).
All four mealybug speciesare polyphagous and their host plants include common commercial and ornamental plant species in Australia. Planococcus lilacinus attacks over 65 genera in 35 plant families. Hosts of Pl. kraunhiae include Citrus, Diospyros kaki (persimmon), Magnolia grandiflora and Portulaca; hosts of Ps. comstocki include Citrus, Musa, Pyruscommunis (pear), poplar, honeysuckle and gardenias, and hosts of Ps. cryptus include Citrus, Vitis vinifera (grapes),Mangifera indica (mango), guava and Bauhinia (CAB International 2007, Appendix B).
The peel of infested fruit is likely to be disposed of by commercial or domestic rubbish systems. However, some fruit waste may be disposed of in the home garden, which provides an opportunity for these pests to transfer to susceptible hosts in the vicinity.
The capacity of mealybugs to produce large numbers of offspring and the consequent persistence of these pests makes them successful colonisers, despite their limited ability to self-disperse. Mealybugs have a relatively high reproductive rate, providing the capacity to rapidly establish a significant population after an incursion. Adult females are generally long-lived and fecund.
Reproduction of Ps. comstocki has two generations per year on apple in New York in the USA; and three generations per year on apple in China and Korea (Agnello et al. 1992; Joen et al. 2003; Liu 2004). In Crimea, females lay 100–250 eggs each and the first generation develops in 27–30 days and the second in 45–50 (CAB International 2007). This species overwinters in bark crevices, soil or roots (Agnello et al. 1992; CAB International 2007). Reproduction, survival and longevity are also greatest at temperatures between 22oC and 26oC and reduced at 30oC (Heidari 1999). The gross reproduction rate was 57–249 eggs per female (Heidari 1999). In Russia, low winter temperatures, and fluctuations in temperature and relative humidity in spring, resulted in a low population density during the development of the first generation (Oganesyan and Babayan 1979). Similar climatic conditions can be found in Australia and it is expected that all species would reproduce in the event that they would be introduced.
Information on the biology of Pl. lilacinus, Pl. kraunhiae and Ps. cryptus is scarce. The complete lifecycle of Pl. lilacinus in Java is about 40 days. Regarding Pl. kraunhiae, the lower developmental threshold temperatures for nymphal development on citrus leaves were reported as 8.0C and 519 degree days (Arai 1996).
The generalist feeding behaviour, past invasive history in other countries and relatively high fecundity of these mealybug species all support a risk rating for establishment of ‘High’.
Probability of spread
The likelihood that mealybugswill 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 the pest, is: HIGH.
The Australian climate is likely to be conducive for the spread of all four mealybug species. The world distribution suggests that all species could be expected to become widespread once established in Australia (see Establishment, above; CAB International 2007).
As all four species are polyphagous (see Establishment, above), susceptible hosts are likely to be available adjacent to sites of establishment, and therefore increase the potential for spread.
Lack of a longer range active dispersal mechanism may moderate the rate at which mealybugs spread. However, first instar nymphs which are the primary dispersal phase within the mealybug’s life-cycle, are capable of active dispersal by crawling and passive dispersal by wind currents and movement of adults or nymphs on infected plant material or on animals (Ben-Dov 1994). Females are wingless, but retain legs and mobility until ovisac development and egg production commences (CAB International 2007). Adult males, although winged are fragile, non-feeding and short-lived (2–7 days) (Mau and Kessing 2000).
From experience in the USA, after establishment of second and subsequent generations of mealybugs, they are likely to persist indefinitely and will spread (Miller et al. 2002).
Polyphagy, dispersal of nymphs and adults, and the past history of spread in other countries of all four species all support a risk rating for spread of ‘High’.
Probability of entry, establishment and spread
The likelihood that mealybugs will be imported as a result of trade in fresh unshu mandarin fruit from the production area in Japan, 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 mealybugs for Australia is LOW.
Internationally, all four mealybug species, i.e. Planococcus kraunhiae, Planococcus lilacinus, Pseudococcus comstocki, and Pseudococcus cryptus areeconomically significant pests of many crops (refer to Appendix B; refer to Establishment, above).
Theycan cause direct harm due to their extraction of sap from their hosts. This direct damage and the development of sooty mould that grows on honeydew excreted by these species can reduce fruit quality, photosynthesis, tree vigour and productivity (CAB International 2007). Although the mouth parts of mealybugs rarely penetrate beyond the fruit epidermis, spotting of fruit at feeding sites and fruit distortion can occur (CAB International 2007).
Existing biological control programs and insecticide treatments would reduce the impact of these pests in commercial production.
All four mealybug species have a wide host range, which includes commercial fruit trees, ornamental shrubs and creepers, amenity trees of tropical, subtropical and temperate distribution and natives (Appendix B; refer to Establishment, above). These mealybug species are therefore likely to become widespread if introduced into a new environment.
They also could compete with native mealybugs, disrupt natural biocontrol methods for other pests, and alter aspects of the biotic environment such as native invertebrates and species known to predate mealybugs (CAB International 2007).
The wide host range and potential for some impact on plant vigour suggests that impacts on amenity plants and ecological communities are likely.
Eradication, control etc.
Impact score: D – significant at the district level
Additional programs to minimise the impact of these pests on host plants may be necessary. Existing control programs can be effective for some hosts (for example, broad spectrum pesticide applications) but not all hosts (for example, where specific integrated pest management programs are used). Existing IPM programs may be disrupted because of the need to re-introduce or increase the use of organophosphate insecticides. Alternatively, new bio-control agents may need to be introduced to supplement IPM programs to control these mealybug species. This may result in a subsequent significant increase in cost of production. Additionally, costs for crop monitoring and advice by consultants to manage the pest may be incurred by the producer. Attacked fruit is considered of lower quality and is often unmarketable.
Impact score: D – significant at the district level
Domestic trade is likely to be disrupted as a result of the entry, establishment and spread of exotic mealybugs. Furthermore, interstate trading restrictions may be introduced, leading to a loss of markets for a number of commodities, which in turn would require industry adjustment. The scope and severity of restrictions are difficult to estimate. However, these pests are polyphagous and therefore impacts are likely to be felt on a broad range of industries. The presence of any of these mealybugs on a commercial crop may result in intrastate and interstate restrictions on the sale and movement of a wide range of fruit and other commodities.
Impact score: D – significant at the district level
The presence of these pests in commercial production areas of a range of commodities that are hosts to these mealybugs may limit access to overseas markets where these pests are absent.
Environmental and non-commercial
Impact score: B – minor at the local level
Mealybugs introduced into a new environment will compete for resources with native species. While existing mealybug eradication programs, which include biological control, may contain introduced mealybugs, additional pesticide applications or other activities would be necessary to manage these pests on susceptible crops. Any additional insecticide usage may affect the environment.