There have been approximately 81 interceptions of scale insects (eg: Chrysomphalus dictyospermi, Parlatoria cinerea, Lepidosaphes sp., Aonidiella sp) on imported limes inspected at the border over the period 2003-2006 (MAF unpubl. 2007)
Other diaspidids and coccids have been intercepted on various Citrus species in this time period (MAF unpubl. 2007)
Scale insects are small and often inconspicuous, usually living around the sepal or under the calyx of the fruit from flowering onwards-eg: Parlatoria pergandii will usually be found near or under the calyx (Smith et al. 1997) (Biosecurity Australia, 2006). Eggs, crawlers and adult
scale insects on fruit would survive the transit time to New Zealand from Samoa (approx. 4 hrs by air freight).
Therefore it is considered the likelihood of entry for all the scale species is considered to be high.
13.5.2. Exposure assessment
The requisites for exposure of scale infested citrus fruit to suitable hosts will be the lifestage of the scale, the environmental conditions and the proximity to potential hosts. A recently mated female or parthenogenetic scale about to lay or already laying eggs could survive in warm, dry or slightly humid conditions allowing the eggs to hatch. Newly hatched crawlers have the greater likelihood of exposure, but are also susceptible to desiccation. Although they actively disperse only over very short distances, scale insects may disperse over several kilometres by wind (Greathead, 1990). In the urban and rural environments near the point of arrival in New Zealand there will be suitable hosts for the scale species considered in this risk analysis.
Infested fruit or peel may be discarded on the roadside, in reserves or open composts. However crawlers are likely to suffer high mortality, therefore the likelihood of exposure is considered to be low but non negligible.
13.5.3. Establishment assessment
The scale insects considered in this risk analysis have a subtropical and tropical range. Those that are also found in temperature regions are usually found in greenhouses or under glass. For most of these scale the optimal temperature range for development is between 22-38˚C with a relative humidity between 50-75% (Andrade and Busoli, 2004; Salama, 1970; Bruwer 1998; Arias-Reveon and Browning 1995; Su and Lin, 1986). Aspidiotus destructor females have a development threshold of 10.5˚C and males 8.7˚C (Zhou et al. 1993). A. destructor can produce 3 generations annually in China, overwintering on Actinidia (Zhou et al. 1993). Unaspis citri has an estimated developmental threshold of 12˚C (Arias-Reveon and Browning, 1995) and Chrysomphalus aonidum 10.6˚C (Klein 1937). Chrysomphalus dictyospermi completes its entire lifecycle in 91 days at 18ºC and 71 days at 25 ºC (Cabido- Garcia 1949). In Turkey Chrysomphalus dictyospermi overwinters as first or second instar nymphs (Tuncyurek and Oncuer 1974) and in Italy as young adults (Vigianni and Iannaconne 1972).
Table 14 Monthly mean temperatures (˚C) for the warmest (February) and coldest (July) months (based on NIWA data for 1971-2000)
February July City
Mean daily
minimum Monthly mean Mean daily maximum Mean daily minimum Monthly mean Mean daily maximum
Kaitaia 15.6 20.0 24.5 8.7 12.2 15.6 Whangarei 15.7 20.0 24.2 7.2 11.2 15.1 Auckland 15.8 19.8 23.7 7.1 10.8 14.5 Tauranga 14.7 19.2 23.8 5.2 9.7 14.3 Gisborne 13.6 18.9 24.2 4.6 9.3 14.1 Napier 14.5 19.3 24.1 4.6 9.3 14.1 Nelson 12.9 17.7 22.4 1.6 7.0 12.4 Mean monthly relative humidity in the above areas range from 73.2 to 88.7%, which is
similar to Samoa (average 80% RH). Citrus fruit coming from Samoa is likely to arrive in Auckland during the summer months.
Some exotic scale species such as Ceroplastes destructor and Lepidosaphes beckii have established in New Zealand despite their tropical/subtropical distribution (Scalenet 2007; Henderson 2001).
Given that Aspidiotus destructor, Chrysomphalus dictyospermi, and Pseudaulacaspis pentagona overwinter in cold climates the likelihood that these three species could establish in the northern parts of the North Island, on the East Coast or the northern part of the South Island, and elsewhere in protected environments such as greenhouses or glasshouses, is high. There is evidence that Chrysomphalus aonidum females can survive temperatures down to freezing point before death occurs (Mathis 1947). Numerous authors have reported the fact that freezing temperatures markedly reduce C. aonidum populations (Thompson & Griffiths 1949). Given the development thresholds of C. aonidum, and Unaspis citri, these two species are also likely to establish in the northern parts of the North Island, around the Bay of Plenty, the East Coast, and elsewhere in protected environments such as greenhouses or glasshouses. Lepidosaphes gloveri, Parlatoria cinerea and Parlatoria pergandii, are likely to survive the summer months in favourable microclimates of the North Island and may suffer population reductions over the winter.
Coccus viridis is more likely to be restricted to establishment in the far north or under glasshouse conditions.
Although a tropical species Ischnaspis longirostris has established in cool temperate countries (eg: Ireland, Denmark, Sweden, Northern USA) under glasshouse conditions. Howardia biclavis also established in temperate climes under the same conditions (Watson 2005). These two species could establish in the far north or anywhere under glasshouse conditions.
There is insufficient information on Aonidiella inornata and Pinnaspis strachani, but both are recorded from tropical areas. It is more likely these two species could survive the summer in the far north, and are unlikely to survive the winter unless under glasshouse conditions Therefore the likelihood of establishment for these 13 scale insects is considered to vary from low to high.
13.5.4. Consequence assessment
13.5.4.1 Economic impact
Apart from ornamentals, the crop species most likely to be affected by the establishment of any of these scale insects include kiwi fruit, Citrus, avocado, peach, pears, pine trees, eucalyptus, apple, capsicums, tomatoes, brassicas, olives, Cucumis sp. and grapes. All 13 species of scale considered in this analysis are polyphagous and some highly
polyphagous (eg: C. dictyospermi has hosts belonging to 73 plant families, A. destructor has hosts belonging to 75 genera in 44 plant families and P. pentagona has over 300 hosts in 78 plant families).
Fruit are affected by feeding damage from diaspidids and coccids and production of honeydew by Coccus viridis allows sooty mould development which decreases tree vigour and health. Fruit appearance is affected by sooty mould either reducing the fruit quality or volume available for sale thereby incurring financial loss from export and domestic markets. Severe infestations of diaspidids can form heavy crusts, causing branches or trees to die (CPC 2008). P. pentagona is the subject of quarantine regulations in many countries and
establishment in New Zealand would cause disruption of access to some markets (eg: Western Australia).
Scale insects, especially diaspidids are difficult to control once established due to their protective covering and control measures incur costs to industry.
The economic consequences across forestry, horticulture and nursery sectors is likely to be high.
13.5.4.2 Environmental impact
It is likely most of these scale insects will find exotic hosts within their usual host range as many exotic plants are already present in New Zealand. However 4 of the 28 exotic
Diaspidids that have established in New Zealand have also found endemic hosts in native forest (Charles and Henderson 2002). These authors comment that the polyphagous nature of scale insects should not be underestimated. Overseas, both Chrysomphalus species have been recorded on Dodonaea vicosa. C. dictyospermi and P. strachani have been recorded on orchids (Williams and Watson 1990; CPC 2007).
Many New Zealand native plants are used for amenity and domestic plantings in this country and this increases the availability of natives and a conditioning to them as potential host species. As scale insects often disperse by wind as crawlers, in time it can be expected some will eventually establish in native bush reserve areas within or close to urban areas. The honeydew secreting species such as C. viridis are likely to attract Vespula wasps, (Beggs 2001) which are nuisance species that disrupt outdoor activities. The limiting factor in this spread is likely to be a combination of wet and cold habitats.
Therefore the likelihood of unwanted environmental consequences is considered to be high.
13.5.4.3 Human health impact
Scale insects are not known to directly impact on human health. However honeydew
excreting species can indirectly affect people by attracting nuisance species such as wasps and ants, whose stings and bites can cause severe reactions in people allergic to them.
13.5.5. Risk estimation
The likelihood of scale insects entering the country is high, the likelihood of exposure is low and the likelihood of establishment varies from low to high depending on the species. If they were to establish then the consequences would be high. The risk estimation for all 13 scale insects considered in this risk analysis is non negligible. Therefore these organisms are classified as hazards in this commodity and risk management measures can be justified.