Laboratory host range testing of Neomusotima conspurcatalis (Lepidoptera: Crambidae) – a potential biological control agent of the invasive weed,Old World climbing fern,Lygodium microphyllum (Lygodiaceae)

Old World climbing fern, Lygodium microphyllum, is a serious invasive weed in south Florida. Development of biological control is vital for sustainable management of L. microphyllum. Neomusotima conspurcatalis was discovered in Hong Kong in 1997 and was subsequently found causing feeding damage on L. microphyllum in much of its native range in Asia. Quarantine testing of N. conspurcatalis used 37 non-Lygodium fern species representative of New World genera of cultivated ferns and fern allies, one gymnosperm, three crop species, six Lygodium species, and the primary host L. microphyllum. No significant oviposition or feeding was observed on any of the 41 non-Lygodium species evaluated. Oviposition and feeding occurred on all Lygodium species, but amounts were low and usually significantly less than observed on L. microphyllum. The exception was L. japonicum, which was preferred as an oviposition host. Neomusotima conspurcatalis was only able to complete development on L. japonicum and L. palmatum, but survival on these species was only half that occurring on L. microphyllum. Neomusotima conspurcatalis is a Lygodium specialist. Lygodium japonicum is an invasive weed in the United States. Lygodium palmatum is restricted to areas of the United States where freezing winter temperatures would be lethal to N. conspurcatalis. It was concluded that N. conspurcatalis would pose no threat to native or cultivated plants in North America or the Caribbean and should be considered for biocontrol of L. microphyllum. A release petition was submitted in 2005. An USDA-APHIS release permit for N. conspurcatalis was issued in 2007.     

Establishment of an imported natural enemy,Neomusotima conspurcatalis (Lepidoptera: Crambidae) against an invasive weed,Old World climbing fern,Lygodium microphyllum,in Florida

Neomusotima conspurcatalis established populations against L. microphyllum at three locations in Florida during 2008. A total of 31,091 insects were released. Ten months later populations estimated at 1.6 to 8.2 million larvae per site had defoliated over 14,000 m² of L. microphyllum. Findings look promising for biocontrol of L. microphyllum in Florida.     

Laboratory studies on the biology and host range of Dichrorampha odorata (Lepidoptera: Tortricidae), a biological control agent for Chromolaena odorata (Asteraceae)

Dichrorampha odorata (Lepidoptera: Tortricidae) is a moth from Jamaica whose larvae bore into, and kill, the shoot tips of the invasive alien plant, Chromolaena odorata (L.) King and Robinson (Asteraceae). This study reports aspects of the biology of D. odorata, and also determined the host specificity (larval and adult no-choice trials) of the moth. Adults were short lived (ranging from 2 to 7 days), with females laying a mean of 15.4 eggs. Eggs took 9 days to hatch, larvae 20–23 days to develop and the pupal stage lasted 11–12 days, giving an overall lifecycle period of 41–45 days. Larval no-choice tests using 34 asteraceous test species indicated that only C. odorata could sustain complete development of D. odorata to adulthood, although there was slight initial boring 14 test species (plus chromolaena). Results from the adult nochoice trials, in which seven test-plant species were exposed to D. odorata, were consistent with those from larval trials, with larval damage, pupae and adults of D. odorata recorded from only C. odorata. This confirmed that only C. odorata is a suitable host for D. odorata in South Africa. Permission has subsequently been granted for the release of D. odorata in South Africa, thus making it the first shoot-tip attacking agent to be released against C. odorata. It is hoped that in the field, high levels of damage by the moth will reduce the height and therefore competitiveness of C. odorata, thereby contributing to the success of biological control of this plant.     

An ultrastructural study of the relationship between the mite Floracarus perrepae Knihinicki & Boczek (Acariformes: Eriophyidae) and the fern Lygodium microphyllum (Lygodiaceae)

Abstract  The ultrastructure of the mite Floracarus perrepae was investigated in relation to its host, Lygodium microphyllum , the Old World climbing fern. Floracarus perrepae has been suggested as a means of biological control for the fern, which is an aggressive weed in tropical areas. Feeding by the mite induces a change in the size of epidermal cells, and cell division is stimulated by mite feeding, causing the leaf margin to curl over into a roll with two to three windings. The enlarged epidermal layer greatly increases its cytoplasmic contents, which become a nutritive tissue for the mite and its progeny. Damage by the mite ultimately debilitates the fern. The structure and depth of stylet penetration by the mite, and the thickness of the epidermal cell wall of L. microphyllum , do not appear to account for the mite's differential ability to induce leaf rolling in its co-adapted host from south-east Queensland but not in the invasive genotype of the fern in Florida.     

The leafmining Leurocephala schinusae (Lepidoptera: Gracillariidae): not suitable for the biological control of Schinus terebinthifolius (Sapindales: Anacardiaceae) in continental USA

The host range of Leurocephala schinusae Davis & Mc Kay (Lepidoptera: Gracillariidae) was studied to assess its suitability as a biological control agent of Schinus terebinthifolius Raddi (Anacardiaceae), a serious environmental weed in the USA and elsewhere in the world. The host range was determined in the laboratory with adult no-choice oviposition (Argentina and USA) and larval development tests (USA). Seventeen plant species in ten genera were selected based on taxonomic relatedness to S. terebinthifolius, economic importance, and availability. Additional information was obtained by sampling foliage of S. terebinthifolius and six other South American native Anacardiaceae species in north-eastern Argentina. In the laboratory, except for Lithrea molleoides and Spondias mombin, all of the tested species were accepted for oviposition with a marked preference for Rhus aromatica. Incipient mines successfully developed into complete mines, pupae and adults on R. aromatica, Rhus copallinum, Schinus molle, Schinus lentiscifolius and S. terebinthifolius. In the field, although L. schinusae showed a clear preference for S. terebinthifolius, the host range, as determined by samples of host use in the native range, included three other Schinus species (S. lentiscifolius, Schinus longifolius, Schinus weinmannifolius) and one Astronium species (Astronium balansae). In conclusion, L. schinusae will not be considered for the biological control of S. terebinthifolius in continental US. However, the utilisation of this species in other infested areas such as Hawaii and Australia should be further discussed.     

Biology and host range of Platyphora semiviridis, a leaf beetle evaluated as a potential biological control agent for Solanum mauritianum in South Africa

The South American tree Solanum mauritianum is a major environmental weed in the high-rainfall regions of South Africa and has been targeted for biological control. Potential agents included five species of the genus Platyphora, which were imported from South America in 1994. Platyphora species associated with Solanaceae reputedly have very specific habitat requirements and host plant preferences in the field. Despite this, host-specificity tests on one species, Platyphora semiviridis, revealed a broad physiological host range. Although laboratory tests showed that P. semiviridis is confined to Solanum species and cannot survive on solanaceous crops outside that genus, it developed on potato and cultivated eggplant (aubergine) as well as on 10 native South African Solanum species. With few exceptions, there were no consistent differences in survival and duration of development on these compared with S. mauritianum. Furthermore, at least six of these non-target species, including potato and eggplant, supported breeding colonies of the beetles in cages. During choice tests in both small and larger cages, P. semiviridis avoided potato but did not consistently discriminate between S. mauritianum, eggplant and six native solanums for larviposition. Despite these findings, P. semiviridis has never been recorded on either potato or eggplant in South America, where it was only observed to feed on S. mauritianum. Although there are several reasons why P. semiviridis is unlikely to attack non-target Solanum species in the field, it will not be released in South Africa because there are other imported agents which have displayed narrower physiological host ranges and which may be more effective.     

Host-range and cold temperature tolerance of Floracarus perrepae Knihinicki & Boczek (Acari: Eriophyidae), a potential biological-control agent of Lygodium microphyllum (Pteridophyta: Lygodiaceae)

Abstract The leaf galling eriophyid mite Floracarus perrepae is a widespread and damaging herbivore of Old World climbing fern, Lygodium microphyllum , across its native range in tropical and subtropical Asia and Australia; and was therefore selected as a candidate biological-control agent for the invasive fern in Florida, USA. The host testing of F. perrepae focused on Lygodium species from North America and the Neotropics, along with threatened or endangered ferns from Florida. Sporeling ferns were used for the initial no-choice screening and F. perrepae showed normal development on the Florida genotype of L. microphyllum with 33.0 ± 4.6 mites per marginal leaf roll gall, modest development on the North American native Lygodium palmatum with 29.0 ± 9.3 mites per roll, and minor development on six other fern species (4.0–0.3). Leaf rolls were induced only on Lygodium species and full rolls were common only on L. microphyllum . These same six non-target plant species were tested again as more mature plants in both no-choice and choice tests and F. perrepae developed only on L. microphyllum . Lethal minimum temperature and cold stress tests were also conducted on F. perrepae . These tests revealed that it would not likely establish north of USDA hardiness zone 8a (−9.5 to −12.2°C), which means it would not overlap with L. palmatum from temperate North America. Our studies conclude that F. perrepae is specific to L. microphyllum , poses little or no risk to native or cultivated ferns in North and South America, and therefore should be considered for release in Florida.     

Gallerucida bifasciata (Coleoptera: Chrysomelidae), a potential biological control agent for Japanese knotweed (Fallopia japonica)

Host specificity of foreign natural enemies are becoming more and more critical in classical biological control programs, as concerns about potential risk from introduced biocontrol agents have been increasing recently. Understanding the insect's fundamental and ecological host ranges is the first step in determining the potential for introduction of an insect to control invasive plants. Japanese knotweed, Fallopia japonica (Houttuyn) Ronse Decraene (Polygonaceae) is an invasive weed in the United States and Europe. A leaf beetle, Gallerucida bifasciata (Coleoptera: Chrysomelidae) is an important natural enemy attacking this plant in Asia. However, its host range records were ambiguous. This study examined the beetle's host specificity through a set of choice and no-choice tests in the laboratory and field in its native China. Gallerucida bifasciata larvae were able to complete development on seven of 87 plant species in larval development tests, while adults fed and oviposited on 10 plants in no-choice tests. Multiple choice tests showed adults strongly preferred Fallopia japonica, Persicaria perfoliata (L.) H. Gross and Polygonum multiflorum Thunb over all other plants. Open field tests and field surveys further revealed that these three species were in its ecological host range. The results of this study suggest that G. bifasciata is a potential promising agent for control of Japanese knotweed in the United States and Europe, although additional host specificity tests and risk assessment should be completed.     

Quarantine host range of Bikasha collaris,a potential biological control agent of Chinese tallowtree (Triadica sebifera) in North America

Chinese tallowtree, Triadica sebifera (L.) Small (Euphorbiaceae), is one of the worst invasive weeds of the southeastern USA impacting coastal wetlands, forests, and natural areas. Traditional mechanical and chemical controls have been unable to limit the spread, and this invasive species continues to expand its range. A proposed biological control candidate, the flea beetle Bikasha collaris (Baly) (Coleoptera: Chrysomelidae), shows high specificity for the target weed Chinese tallowtree. Results from a series of no‐choice and choice feeding tests of B. collaris adults and larvae indicated that this flea beetle was highly specific to Chinese tallowtree. The larvae of B. collaris feed by tunneling in the roots, whereas the adults feed on the leaves of Chinese tallowtree. A total of 77 plant taxa, primarily from members of the tallow plant family Euphorbiaceae, were tested in numerous test designs. Larval no‐choice tests indicated that larvae completed development only on two of the non‐target taxa. Of 80 B. collaris larvae fed roots of Hippomane mancinella L. and 50 larvae fed roots of Ricinus communis L., two and three larvae completed development, respectively. The emerging adults of these five larvae died within 3 days without reproducing. Larval choice tests also indicated little use of these non‐target taxa. Adult no‐choice tests indicated little leaf damage by B. collaris on the non‐targets except for Ditrysinia fruticosa (Bartram) Govaerts & Frodin and Gymnanthes lucida Sw. When given a choice, however, B. collaris adults consumed much less of the non‐targets D. fruticosa (7.4%) and G. lucida (6.1%) compared with the control leaves. Finally, no‐choice oviposition tests indicated that no eggs were produced when adults were fed all non‐target taxa, except those fed G. lucida. These B. collaris adults fed G. lucida leaves produced an average of 4.6 eggs compared with 115.0 eggs per female when fed Chinese tallowtree. The eggs produced from adults fed G. lucida were either inviable or the emerging larvae died within 1 day. These results indicate that the flea beetle B. collaris was unable to complete its life cycle on any of the non‐target taxa tested. If approved for field release, B. collaris will be the first biological control agent deployed against Chinese tallowtree in the USA. This flea beetle may play an important role in suppressing Chinese tallowtree and contribute to the integrated control of this invasive weed.     

Biology and host range of the stem-boring beetle Aphanasium australe, a promising agent for the biological control of Hakea sericea in South Africa

The invasive Australian shrubHakea sericea Shrader is a majorenvironmental weed in the Western and EasternCape Provinces of South Africa. Dense,impenetrable thickets severely threaten theunique endemic vegetation of the Cape FloristicKingdom, increase fire hazards and reduce wateryields in catchments. Biological control,initiated in the 1970s, is largely confined tothe use of seed-feeding insect agents. Becausenone of these agents reduce the density ofexisting hakea populations, a stem-boringbeetle, Aphanasium australe (Boisduval) (Cerambycidae),was imported into quarantine in South Africa in1975. During multichoice oviposition tests,involving 12 Australian and six South Africanproteaceous species, in a walk-in cage, A. australe only oviposited on four species ofHakea and two exotic species of Grevillea. However, culturing difficultiesresulted in the suspension of host-specificitytesting after three years. Testing was resumedfollowing re-importations in 1995, also becauseA. australe also attacks Hakeagibbosa (Sm.) Cav., which is not attacked byany of the existing biocontrol agents. Duringno-choice survival tests, involving 66test plant species from 15 families, A. australe only developed on H. sericea, H. gibbosa and one exoticspecies of Grevillea. The contention thatA. australe is confined to the genus Hakea was confirmed by host records andsurveys in Australia which provided no evidenceof attacks on crop, pasture or related plants.The regulatory authorities accepted theseresults and A. australe was cleared forrelease in South Africa during 2001.     

Post-establishment assessment of host plant specificity of Arytainilla spartiophila (Hemiptera: Psyllidae), an adventive biological control agent of Scotch broom,Cytisus scoparius

Scotch broom, Cytisus scoparius (Fabaceae), is a shrub native to Europe that is invasive in the USA, New Zealand and Australia. The psyllid Arytainilla spartiophila has been purposely introduced to Australia and New Zealand as a biological control agent of C. scoparius, but is an accidental introduction to California. Lupines (Lupinus spp.) are the closest native taxon to Cytisus in North America, and are therefore considered to be at the highest risk for non-target damage. However, because no lupines are native to Australia or New Zealand, only one imported forage species was evaluated during prior host specificity testing. We conducted a laboratory nymphal transfer experiment, a field choice experiment and a field survey to assess risk to three lupine species (Lupinus albifrons, Lupinus bicolor and Lupinus formosus). In the laboratory, 20% of third-instar nymphs were able to develop to adulthood on L. formosus but not on the other lupine species, while 40% completed development on C. scoparius. In the field experiment, potted lupine and C. scoparius plants were placed beside large infested C. scoparius plants; oviposition occurred on all the potted C. scoparius plants, but on none of the lupines. In the field survey, no A. spartiophila eggs or nymphs were found on naturally occurring lupines growing adjacent to infested C. scoparius. The results indicate that A. spartiophila is not likely to damage or reproduce on lupines in the field. This study provides an example of how field studies can help clarify the host specificity of biological control agents.     

Biology and field host range of Ceutorhynchus cardariae,a potential biological control agent for Lepidium draba

Lepidium draba (Brassicaceae) is a clonal herb, originating from Eurasia, which is invasive in North America. A classical biological control project was initiated in 2001, and the gall‐forming weevil Ceutorhynchus cardariae was prioritized as a candidate agent. We studied its biology and field host range between 2003 and 2014 in the laboratory and a common garden in Switzerland and in the field in Romania. Ceutorhynchus cardariae is a univoltine to bivoltine species. In Switzerland, oviposition usually started at the beginning of March and can occur at temperatures as low as 2.5°C. Galls are formed on stems, leaf stalks and midribs of L. draba rosettes and bolting plants. Gall size increased with an increasing number of larvae per gall. The three larval instars feed inside the galls and leave the plant to pupate in the soil once mature. In Switzerland, development from egg to adult took about 12 weeks in spring. Adults emerged from May to July. After a brief feeding period, adults aestivate. From late summer, feeding recommenced and females may oviposit, forming a partial second generation. Eggs and all larval instars can be found in galls throughout winter. The rate of larval ectoparasitism reached 78%, while endoparasitism was low with a maximum of 2.3%. Lepidium draba populations differed in their suitability for development (number of C. cardariae produced), indicating that effectiveness of C. cardariae – in case released – may be variable. In the field, we observed that gall formation by C. cardariae can severely stunt or even kill shoots. Investigations on the field host range of C. cardariae indicated that only the closely related Lepidium campestre may act as an alternative host for the weevil in Europe. Host‐specificity tests are underway to determine its environmental safety before field release in North America is being considered.     

Biology and host range of Ophiomyia camarae, a biological control agent for Lantana camara in South Africa

The herringbone leaf-mining fly, Ophiomyiacamarae Spencer, is a promising candidateagent for the biological control of the alieninvasive weed Lantana camara L. in SouthAfrica. During extensive host-specificity testsinvolving 39 test plant species from 12families, survival to adulthood was restrictedto L. camara, L. trifolia, and fourspecies of the closely-related genus Lippia (Verbenaceae) in no-choice tests. However, survival of the immature stages wassignificantly lower on L. trifolia andthe four Lippia species than on L.camara. In addition, O. camaraedisplayed very strong oviposition preferencefor L. camara during paired-choice tests.This narrow laboratory host range suggests thatO. camarae will not pose any risks tonon-target verbenaceous plants if released inSouth Africa. Permission to release O. camaraeinto South Africa was approved by the regulatoryauthorities in 2001.     

Biology and host range of Heterapoderopsis bicallosicollis: a potential biological control agent for Chinese tallow Triadica sebifera

Chinese tallow, Triadica sebifera, is an invasive weed that infests natural and agricultural areas of the south-eastern USA. A candidate insect for biological control of Chinese tallow has been studied under quarantine conditions. The biology and host range of a primitive leaf-feeding beetle, Heterapoderopsis bicallosicollis, were examined between July 2008 and February 2010. H. bicallosicollis adults fed on 16 of 29 non-target species and survived >10 days on all 29 species, more than the number of days that adults survived when deprived of food. Additionally, adult feeding, oviposition and partial larval development occurred on a Florida endangered species, Heterosavia bahamensis. These data indicated that H. bicallosicollis adult feeding and oviposition may not be limited to the target weed and included several valued North American natives. Therefore, as its release could pose unacceptable risks, testing of this species was discontinued and the quarantine colony destroyed.     

Distribution, biology and host range of Rhembastus sp. (Coleoptera: Chrysomelidae), a candidate for the biological control of Bryophyllum delagoense (Crassulaceae) in Australia

The biology and host range of a leaf-beetle, Rhembastus sp. (Coleoptera: Chrysomelidae: Eumolpinae) from Madagascar, was studied under quarantine laboratory conditions in South Africa to determine its potential as a biological control agent of Bryophyllum delagoense (Ecklon & Zeyher) Schinz (Crassulaceae) in Australia. Favourable attributes of the beetle include relative ease of culturing, multiple generations per year, and high levels of damage inflicted by adults, which feed on the plantlets produced at the end of each leaf, and root feeding larvae. The adults therefore have an impact on the reproductive potential of the plant and larval feeding on the roots hampers the uptake of water and may even facilitate secondary infections by pathogens. Despite indications from field surveys in Madagascar that Rhembastus sp. has a narrow host range, preliminary no-choice and multiple-choice trials in quarantine revealed that it could complete its development on five non-target species in the family Crassulaceae. Extensive host range trials still have to be undertaken in Australia before the beetle can be considered for release.     

Laboratory life history and field observations of Poliopaschia lithochlora (Lower) (Lepidoptera: Pyralidae), a potential biological control agent for Melaleuca quinquenervia (Myrtaceae)

Abstract  Melaleuca quinquenervia (Cav.) S.T. Blake, Australian broad-leaved paperbark, has become a serious weed in southern Florida. Poliopaschia lithochlora (Lower) is a promising candidate as a potential biological control agent, and this study describes laboratory and field observations of the life history of this moth. Eggs are laid in small batches, mainly on the surface of leaves, and larvae are voracious leaf feeders, concealed in tubes that are usually found in small colonies attached to leaves and stems. Larvae move from these tubes to feed on surrounding leaves, and saplings and suckers are frequently defoliated. Prepupae form sealed bulbs in the larval tubes in which they pupate. Adult females are mainly active and oviposit at night. Development from egg to adult occurs in approximately 80 d. Field populations appear to be regulated by several egg and larval parasites. Because this moth severely damages saplings and suckers of M .  quinquenervia , prefers low-lying humid sites, and can be successfully mass reared, it is rated highly for its potential as a biological control agent.     

Determining the host specificity of the biological control agent Trichomalus perfectus (Hymenoptera: Pteromalidae): the importance of ecological host range

We determined the host range of the parasitoid Trichomalus perfectus (Walker), a candidate for classical biological control of cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham), an important pest of canola in Canada. Studies were conducted in Europe and in North America. In laboratory experiments, the levels of parasitism (acceptance) of Ceutorhynchus turbatus Schultze, C. cardariae Korotyaev, C. omissus Fall and C. querceti (Gyllenhal) by T. perfectus were not significantly different than of the target host C. obstrictus. Although C. typhae (Herbst), C. pallidactylus (Marsham), C. americanus Buchanan, C. neglectus Blatchely and Ceutorhynchus sp. nr. nodipennis were parasitised by T. perfectus, the levels of parasitism were significantly lower on these species than on C. obstrictus. Ceutorhynchus peyerimhoffi Hustache, C. erysimi (Fabricius), C. alliariae H. Brisout, C. roberti Gyllenhal, Mogulones borraginis (Fabricius), Mononychus vulpeculus (Fabricius) and the leaf-mining fly Scaptomyza flava (Fallén) were not attacked. Ecological host range surveys in Europe corroborated the prediction that T. perfectus would attack C. cardariae at similar rates to C. obstrictus. In North America, the recent discovery of T. perfectus in a C. omissus population suggests that laboratory findings predicting that C. omissus is a preferred host may be the case in the field. We found that T. perfectus attacks larvae of some Ceutorhynchus spp. feeding on Brassicaceae and does not attack species outside of that host range. Thus, the parasitoid can be defined as narrowly oligophagous. These results demonstrate the value of ecological host range studies in the area of origin to validate hypotheses generated through laboratory host range experiments.     

Host range and risk assessment of Zygogramma bicolorata,a defoliating agent released in South Africa for the biological control of Parthenium hysterophorus

Parthenium hysterophorus (parthenium) is a weed of international importance and is spreading rapidly in sub-Saharan Africa. Consequently, it has been targeted for biocontrol in South Africa since 2003. Based on precedents elsewhere in the world, the defoliating beetle Zygogramma bicolorata was prioritised as a candidate agent. Although no-choice tests, involving some 48 test plant species, indicated a significant preference for parthenium, significantly reduced feeding and oviposition was recorded on some species. Multiple-choice tests resolved many of these non-target results; however, Helianthus annuus (sunflower) was still selected for oviposition and feeding. Of the 12 sunflower cultivars tested, four were selected for oviposition, while two were selected for oviposition and feeding. These six cultivars were then subjected to larval development trials, together with three native and two weed species (in the Asteraceae). These trials showed high levels of complete development on parthenium, significantly reduced development on sunflower cultivars, and partial development on only one of the weed species. Finally, a risk assessment was conducted on the six sunflower cultivars to quantify Z. bicolorata feeding and reproductive performance. Feeding risk calculations revealed these cultivars to have an extremely low risk (<0.2%) of supporting Z. bicolorata feeding and development. Similarly, reproductive risk calculations showed a very low risk (<0.16%) of supporting viable Z. bicolorata populations. These data are supported by findings from both the native (Mexico) and introduced ranges (Australia, India) of Z. bicolorata, where it has never been recorded as a pest of sunflower. These considerations were accepted by the regulatory authorities and in August 2013, Z. bicolorata became the second insect agent to be released in South Africa for the biocontrol of parthenium.     

The host specificity of Anomalococcus indicus Ayyar (Hemiptera: Lecanodiaspididae), a potential biological control agent for prickly acacia (Vachellia nilotica ssp. indica) in Australia

ABSTRACT

Prickly acacia, Vachellia nilotica ssp. indica (Benth.) Kyal. & Boatwr, is a significant weed of northern Australia and has been a target of weed biological control in Australia since the 1980s. Following native range surveys in India, the scale insect Anomalococcus indicus Ayyar was identified as the most promising agent and was imported into Australia for further research. A. indicus is a major pest of prickly acacia on the Indian subcontinent, where it causes shoot tip dieback and plant death. Despite field observations suggesting the species was specific to V. nilotica, A. indicus completed development on 17 of the 84 non-target plant species tested during no-choice host specificity trials under quarantine conditions. Of these, Acacia falcata, V. bidwillii, V. sutherlandii and Neptunia major supported high numbers of mature females in all replicates. All of these species were utilised in choice trials. Combined risk scores indicate that V. sutherlandii, N. major and A. falcata may be attacked in the field. Due to the limited ability of scale insects to disperse, only those non-target species that occur on the Mitchell grass downs (i.e. V. sutherlandii) are considered to be at risk. Nevertheless, in view of the disparity between quarantine test results and the observed field host specificity of A. indicus in India, field trials are currently being conducted in India using Australian native species on which complete development has occurred. The future of A. indicus as a biological control agent for prickly acacia in Australia will be determined once results from these field trials are known.