Session 9 Post-release Evaluation and Management 409 Host Specificity Testing, Release and Successful Establishment of the Broom Gall Mite (Aceria genistae) in Australia and New Zealand for the Biological Control of Broom (Cytisus scoparius) J. -L. Sagliocco1, A. Sheppard2, J. Hosking3, P. Hodge4, Q. Paynter5, H. Gourlay6 and J. Ireson7 1Biosciences Research Division, Department of Primary Industries, Frankston, 3199, Victoria, Australia [email protected] 2CSIRO Ecosystems Sciences, GPO Box 1700, Canberra, 2601, ACT, Australia [email protected] 3Department of Primary Industries, Tamworth Agricultural Institute, Calala, 2340, NSW, Australia [email protected] 4c/o CSIRO Ecosystems Sciences, GPO Box 1700, Canberra, 2601, ACT, Australia 5Landcare Research, St Johns, Auckland, 1072, New Zealand [email protected] 6Landcare Research, Lincoln, 7640, New Zealand [email protected] 7Tasmanian Institute of Agricultural Research, University of Tasmania, New Town 7008, Tasma- nia, Australia [email protected] Summary A form of the eriophyid mite, Aceria genistae (Nalepa) was tested between 1999 and 2001 against 34 test plant taxa and cultivars from 12 tribes for its specificity towards the invasive shrub Scotch broom, Cytisus scoparius (L.) Link, and was shown to be highly specific. The mite was approved for release in Australia and New Zealand where redistribution and monitoring programs have been put in place. After three years, 106 releases of the mite have been conducted in Australia with a 32% establishment rate. In New Zealand, 40 releases have been made with 50% establishment. Both countries are continuing releasing this mite and are monitoring its establishment. Introduction implement, expensive, have negative environmental impacts and require follow-up due to large seed banks and reinvasion by seedlings and young plants The leguminous shrub Scotch broom, Cytisus (Downey and Smith 2000; Paynter et al 1998). scoparius (L.) Link (Fabaceae) is native to the UK, A number of demography studies have focused western, southern and central Europe. There it is on patterns and processes of broom invasion in its considered moderately weedy and it occasionally native range (France) (Paynter et al. 2003; Paynter colonises forest areas and pastures. Elsewhere, it et al 1998) and its introduced range in Australia has become a serious invader in several countries: (Downey and Smith 2000; Paynter et al 2003; eastern and western USA including Hawaii, British Sheppard et al 2002; Waterhouse 1988) and New Columbia, Australia, New Zealand, Chile and Zealand (Paynter et al. 2003; Williams 1981). In India. Mechanical and chemical control methods of addition, studies in the weed’s native range have broom in invaded natural ecosystems are difficult to highlighted the role of natural enemies in limiting XIII International Symposium on Biological Control of Weeds - 2011 410 Session 9 Post-release Evaluation and Management broom performance (Waloff and Richards 1977), as Aceria spartii). Mites identified as A. Genistae especially the potential of arthropods to reduce seed discovered on stunted shoot tips of gorse and production and broom longevity (Rees and Paynter French broom, Genista monspessulana (L.) L.A.S. 1997). Broom plants in Australia and New Zealand Johnson in the USA caused limited damage and are largely devoid of specialist insect herbivores did not develop on any other species (Chan and (Memmott et al 2000), indicating that biological Turner 1998). Similarly, mites identified as A. control may have some potential to control broom genistae were found infesting gorse, U. europaeus in these countries. New Zealand (NZ) began a but not broom, in New Zealand (Manson 1989). broom biological control program by releasing the seed feeding beetle, Bruchidius villosus (Fabricius) Methods and the sap-sucking psyllid, Arytainilla spartiophila (Förster) in 1987 and 1993 respectively. Meanwhile, an accidental introduction of the broom twig-mining Host specificity testing moth, Leucoptera spartifoliella Hübner resulted in extensive damage to broom in NZ south island (Syrett Initial testing of A. genistae by CABI (the et al 1999). Building on New Zealand’s experience, Centre for Agriculture and Biosciences CSIRO (The Commonwealth Scientific and International) and CSIRO was conducted with a Industrial Research Organisation) and the New small number of broom’s close relatives at CSIRO South Wales Department of Agriculture imported European laboratory in Montferrier (France). Field L. spartifoliella from NZ and released it in 1993 tests were carried out under natural conditions in (Wapshere and Hosking 1993), followed by releases a native broom infestation where Cytisus striatus of A. spartiophila in 1994 and B. villosus in 1995 (Hill) Rothm., Chamaecytisus palmensis (H.Christ) (Syrett et al 1999). A fourth agent, the eriophyid gall, F.A.Bisby & K.W.Nicholls, Spartium junceum L., Aceria genistae (Nalepa) was identified as a potential Genista tinctoria L., Medicago arborea L., Laburnum biological control agent during European field anagyroides Medik. and C. scoparius were planted as surveys (Hosking 1990; Syrett et al 1999; Wapshere test plants. After two years, A. genistae galls were only and Hosking 1993). A. genistae was originally on C. scoparius and no attack on any of the species described by Nalepa from galls developing on Scotch tested had been observed. Additional tests were broom in eastern France. The known native range conducted in a glasshouse where A. genistae galls of the mite includes the UK, Italy, Spain and central were tied onto C. palmensis and U. europaeus with Europe. Colonies of A. genistae start at the inner C. scoparius as a control. Gall development occurred base of stem buds and cause growth deformities on on C. scoparius only. The high specificity of the mite bud burst becoming round, pubescent galls. Several towards C. scoparius resulted in comprehensive host overlapping generations develop in galls during specificity study being conducted in Australia. A. spring and summer. Non-woody galls wither in late genistae galls collected in the Cevennes mountains summer and autumn, forcing mites to crawl into range, north of Montpellier (France) were shipped dormant stem buds where they overwinter. Gravid to the CSIRO quarantine facility in Canberra for females are also wind dispersed in spring and rearing and further evaluation against a number of there is a sex ratio of about 1:20 male: females (J-L Australian and New Zealand native plant species Sagliocco pers. obs.). ‘Aceria genistae’ is probably a (Table 1). In quarantine, mites were inoculated onto complex of specific forms or sibling species. It has broom plants where they developed galls, providing been recorded on a number of Genisteae species a large colony for host specificity tests. including Cytisus spp., Ulex europaeus L., Genista There are no Australian native plant species spp. and Spartium junceum L. (Castagnoli 1978). in the tribe Genisteae. Therefore, the focus of the However, Cromroy (1979) (Cromroy 1979) noted testing was on species of economic importance in the that eriophyids are often highly host-specific, even Genisteae and other related tribes in the Faboideae, to the level of plant form. Castagnoli (1978) has plus native species in related tribes, with less shown that A. genistae developing on broom did intensive testing of representative Australian natives not develop on S. junceum, while the mites found in other subfamilies of the Fabaceae. Plants tested for on Spartium are a separate species (redescribed New Zealand included local cultivars of two Lupinus XIII International Symposium on Biological Control of Weeds - 2011 Session 9 Post-release Evaluation and Management 411 species and seven species representing all native In 2002, CSIRO submitted an application to genera with the exception of the monophyletic genus federal agencies to obtain approval for release of Montigena. A. genistae into the Australian environment. After Between 1999 and 2001, 34 taxa and cultivars examining the submission, AQIS (the Australian from 12 tribes were tested as part of the risk Quarantine and Inspection Service) Plant Biosecurity assessment required to obtain release permits for the Australia and the Department of Environment mite in Australia and in New Zealand (Table 1). Each approved release of the mite in the environment. In test consisted of five replicates of one taxon paired 2003, before the mite was released, a broom fungus with five C. scoparius of similar size as controls. Each that had been ruled out as a broom potential biological plant tested had dormant buds required for mite control agent for Australia due to lack of specificity development. A. genistae galls were harvested from (Morin et al 1999) was discovered in the Canberra broom gall-producing plants kept in quarantine, and mite culture (Morin et al 2006). Consequently, the each gall was scored for number of mites present. mite culture had to be destroyed and its release was Five to ten galls with comparable numbers of mites postponed. A lack of funding caused further delays. were then tied onto the foliage of each test plant and In 2006, with joint funding from the Australian control and covered with a plastic bag for 72 hours to Government and the Department of Primary prevent galls drying out too quickly and to encourage Industries (DPI), Frankston, Victoria, Australia mites to migrate out of the galls. Test and control imported the mite into quarantine in Frankston and plants were kept at temperatures of 18° C (day) and a clean colony protocol was developed using the 12° C (night) (10 hrs light: 14 hrs dark) under high transfer of individual mites. Mite populations were intensity artificial light for one month to help mites increased by transferring mites onto new plants colonise plants while there was no bud development. for several generations until approval for release After one month temperatures were increased to 20° was granted. Outside quarantine, broom plants C (day) and 15° C (night) (12 hrs light: 12 hrs dark) were inoculated with mites to provide material for to initiate bud growth resulting in gall formation releases.