(*of regional quarantine concern to Western Australia; ^of regional quarantine concern to Northern Territory, Tasmania; #of regional quarantine concern to Northern Territory, South Australia, Tasmania, Western Australia)
Some Thysanoptera (thrips) species are pests of commercial crops, due to damage caused by feeding on developing flowers, leaves and fruit (CAB International 2007). Their mouthparts are used to rupture and imbibe fluids from plant cells, causing scarring that can reduce crop yield, productivity and marketability (CSIRO 1991). They can also transmit tospoviruses while feeding (CAB International 2007). Thrips are opportunistic, well adapted to surviving difficult conditions, and capable of tolerating temperatures below freezing over extended periods (McDonald et al. 1997).
The thrips considered in this import risk assessment are: Chaetanaphothrips orchidii,Frankliniella intonsa, Frankliniella occidentalisand Thrips palmi. These species have been grouped together because of their related biology and taxonomy. They are predicted to pose a similar risk and require similar mitigation measures. In this assessment, the term ‘thrips’ is used to refer to these species, unless otherwise specified.
4.9.2 Probability of entry
Probability of importation
The likelihood that the thrips assessed will arrive in Australia with the importation of fresh unshu mandarin fruit from the production area in Japan is: HIGH.
Thrips are cold tolerant and may survive low temperatures during storage and transport (CAB International 2007). For example, T. palmi is able to survive temperatures as low as -3°C to -7°C (Nagai and Tsumuki 1990).
The lifespan of F. intonsa adults is up to 49 days (CAB International 2007) which exceeds the packing and transport period (refer to Post-harvest, Chapter 3).
Adult thrips are only 1.3 mm long (Pernezny et al. 2003; QDPIF 2005). Eggs of Frankliniella spp. are small (about 200 μ long) and may be laid on, or under the peel of unshu mandarins (Nakazawa 1981; Tsuchiya et al. 1995).
Damage may appear as scratches, bronzing or silvering to the fruit (CAB International 2007) which at low levels would be difficult to detect.
The cold tolerance, lifespan, small size and cryptic nature of thrips, and their association with fresh unshu mandarin fruit, all support a risk rating for importation of 'High'.
Probability of distribution
The likelihood that thrips will 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.
Adult thrips may hide, feed and lay eggs on, or under the peel of fresh unshu mandarin fruit (Tsuchiya et al. 1995; Pernezny et al. 2003). Although adult thrips will most likely move off the fruit when disturbed, immature instars may remain with the fruit during distribution for wholesale or retail trade.
Thrips are among the weakest flying insects but their finely fringed wings enable them to remain airborne and be easily dispersed by wind (Lewis 1973), and on clothing, hair, contaminated equipment and containers (EPPO 1997). Adult thrips are also able to run and jump (Jenser 1973; EPPO 1997; Pearsall 2002) further increasing their mobility.
Thrips have a wide host range including crop plants and ornamental species, all of which are present in Australia (refer to Appendix B). Chaetanaphothrips orchidii is a polyphagous species attacking commercial fruit trees and vines, including citrus, papaw, passionfruit, tree and shrub species, such as Banksia and oleander, weeds, including lantana (APPD 2008). This thrips is also a major pest of anthuriums (CAB International 2007). Frankliniella intonsa can be found on capsicum, tomato, asparagus, strawberry, peach, nectarine, chrysanthemum, pea, soybean, lucerne, rice and cotton (CAB International 2007). Hosts of F. occidentalis include chrysanthemums, cucurbits, cotton, grapes, citrus and apple (CAB International 2007). Thrips palmi may be present on a range of plants in the families Curcurbitaceae and Solanaceae (Young and Zhang 1998; QDPIF 2005; CAB International 2007).
The intended use of the proposed import of fresh unshu mandarin fruit from Japan is for human consumption. This end use would assist the potential distribution of these thrips species. Disposal of infested fruit or peel into the environment provides the potential for these pests to transfer to susceptible hosts in the vicinity.
The cryptic nature, high mobility and polyphagy of thrips, moderated by their weak flying ability, support a risk rating for distribution of ‘Moderate’.
Probability of entry (importation ´ distribution)
The likelihood that thripswill 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.
4.9.3 Probability of establishment
The likelihood that thrips will establish within Australia, based on a comparison of factors in the source and destination areas considered pertinent to their survival and reproduction, is: HIGH.
Thrips species reproduce rapidly. For example, F. intonsa reproduced up to 22 generations during one year in laboratory experiments, with the egg, larval stage and pupal stage each lasting only 1–3 days (Tang 1976; Pernezny et al. 2003; CAB International 2007). Similar experiments have shown that F. occidentalis can produce up to 15 generations per year (Katayama 1997; McDonald et al. 1998; CAB International 2007) while T. palmi are capable of producing 25–26 generations per year with the entire egg to adult stage taking 10–19 days (Huang and Chen 2004). Adult females of this species lay up to 200 eggs during their lifespan (Wang et al. 1989). Chaetanaphothrips orchidii reproduces parthenogenetically and lays 80 to 100 eggs per female (Hara et al. 2002).
Abiotic factors have a large influence on the abundance of thrips. Frankliniella intonsa and T. palmi develop at faster rates at warmer temperatures (CAB International 2007). Reproductive rates are also improved when temperatures exceed 20°C. The total life-cycle of F. occidentalis is between 15 days at 30°C and 45 days at 15°C (CAB International 2007). Temperatures in the range of 25–30°C are optimal for population growth of T. palmi (Huang and Chen 2004). Chaetanaphothrips orchidii completes its entire life cycle in about 28–32 days during the warm summer months in the USA (Hara et al. 2002). Much of Australia is subject to temperatures between 15°C and 30°C, providing opportunity for establishment. Adult F. intonsa are also more mobile when exposed to temperatures above 20°C (Jenser 1973; CAB International 2007).
Natural enemies and pesticides have controlled populations of thrips with some degree of success (CAB International 2007). However, whilst insecticides have been widely used to suppress F. intonsa populations on plants such as cotton, the success of this treatment is limited (Atakan and Özgür 2001). Control of thrips for long periods is difficult because of their cryptic habit and their known ability to become resistant to pesticides (Herron et al. 1996; Datta et al. 1999; Herron and Cook 2002; CAB International 2007). In addition, differences in pesticide resistance profiles have been observed between F. occidentalis populations in Japan and Australia (Morishita 2001; Herron and James 2005; Zhang et al. 2008). Therefore existing pesticide control practices in Australia may be less effective against Japanese thrips species.
Frankliniella occidentalis is already established in some parts of Australia including Queensland (Mound 2005), New South Wales (Bright et al. 2006), South Australia and Western Australia (NTDPIFM 2007). Thrips palmi occupies some parts of the Northern Territory and south-eastern Queensland. Chaetanaphothrips orchidii occurs in Queensland, New South Wales and South Australia (Mound 2001; APPD 2007). Control measures are currently implemented on interstate transport of known host commodities (Young and Zhang 1998; QDIPF 2005; NTDPIFM 2006; DAFWA 2008c).
Thrips palmi has a wide host range, including plants in the Curcurbitaceae and Solanaceae families (Young and Zhang 1998; QDPIF 2005; CAB International 2007; NTDPIFM 2006) which are widely distributed throughout Australia. Wide host plant distribution would support the spread of pest populations.
The high reproductive rate, pre-adaptation to temperature ranges found in Australia, and limited success of control measures for thrips all support a risk rating for establishment of 'High'.
Probability of spread
The likelihood that thrips 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 the pest, is: HIGH.
Frankliniella intonsa originated in South-East Asia and is now found throughout Europe and Asia where it has established itself as an economically significant pest (CAB International 2007). Frankliniella occidentalis is a native to western North America, but since 1960, it has spread rapidly throughout much of North America, Europe, northern and southern Africa, parts of South America and Asia, Australia and New Zealand (Kirk and Terry 2003). Already present within parts of Australia (NT and Qld), T. palmi is able to spread very quickly (Young and Zhang 1998; CAB International 2007) and has rapidly become a major pest of cucurbits and solanaceous plants in many tropical regions of the world (Young and Zhang 1998; QDIPF 2005; CAB International 2007). Similarly, C. orchidii is present along the eastern seaboard of Australia and South Australia (Mound 2001; APPD 2008). Its polyphagous nature and ability to adapt to a wide climatic range (i.e. of tropical, subtropical and temperate distribution) all support the probability that it could spread to other areas of Australia.
Thrips have a wide host range, including crop plants and ornamental species, all of which are present in Australia (refer to Distribution, above).
Climatic factors, such as deserts, semi-arid and arid areas, can significantly slow the natural spread of these insect pests, due to their low tolerance to low humidity and high temperatures. However, they may be moved with fruit and other plant material.
The vast spread of the four thrips species in other countries over short periods of time, their polyphagy, and the wide distribution of susceptible hosts within Australia, all support a risk rating for spread of 'High'.
Probability of entry, establishment and spread
The likelihood that thrips 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 thrips for Australia is: LOW.
Thrips may cause direct harm to a range of plant hosts. Frankliniella intonsa damages both crop and ornamental species, including capsicum, tomato, asparagus, strawberry, peach, nectarine, chrysanthemum, pea, soybean, lucerne, rice and cotton (CAB International 2007). Frankliniella occidentalis causes direct harm to a wide range of plant hosts, including chrysanthemums, cucurbits, cotton, grapes, citrus and apple (CAB International 2007), all of which are present in Australia. Thrips palmi causes damage to a wide range of hosts, including plants in the Curcurbitaceae and Solanaceae families (QDPIF 2005; NTDPIFM 2006). Chaetanaphothrips orchidii is polyphagous, causing damage to commercial fruit trees, ornamentals, shrubs and weeds (APPD 2008).
Although light infestations of thrips are generally not harmful to plants, more severe infestations can result in damaged fruit, skin 'russeting', delay in production of flowers and fruit, stunting of shoot growth, distorted fruits and a general decline in plant vigour, diminished fruit set, fruit drop, and the occurrence of white swellings and spots caused by oviposition (EPPO 1997; CAB International 2007).
A range of thrips can also act as a vector for a number of tospoviruses, many of which are not known to occur in Australia (Campbell et al. 2008). Viral symptoms vary considerably in different plants, ranging from wilting and collapse of lettuce plants, leaf mottling and distortions, to ring-spotting on tomato fruits, and can lead to the total loss of certain crops (CAB International 2007).
Other aspects of the environment
B – minor at the local level
Thrips introduced into a new environment may compete for resources with the native species. There are no known consequences on other aspects of the environment.
Eradication, control etc.
D – significant at the district level
Existing control programs using pesticides may be effective, though it is difficult to quantify the specific damage caused by thrips. Control programs with broad spectrum pesticide applications could be effective for some hosts, but would need to be supplemented by other methods shown to be effective, such as hygiene measures in glasshouses, as thrips quickly develop resistance to the same pesticide preparations (Herron et al. 1996; Datta et al. 1999; Herron and Cook 2002; CAB International 2007). Introduced thrips species from Japan may have different pesticide resistance profiles and thus existing control programs may be ineffective.
D – significant at the district level
The introduction of thrips species that are not present in Australia is likely to have a significant impact on interstate trade affecting a wide range of host commodities, with potential loss of markets and significant industry adjustment.
D – significant at the district level
Presence of thrips in commercial production areas on a wide range of commodities (e.g. species of Fabaceae, Cucurbitaceae, Solanaceae, Rosaceae and Rutaceae) will impact trade as countries may impose measures that may limit access to overseas markets which lack these pests.
Environmental and non-commercial
B – minor at the local level
Thrips species introduced into a new environment will compete for resources with native species. Additional pesticide applications or other activities would be necessary to manage these pests on susceptible hosts. Any additional insecticide usage may affect the environment.