Besides this introduction, which gives a historical and contextual perspective, this compilation of reviews in African Entomology volume 19(2), comprises 28 papers, 24 of which provide accounts of recent (i.e. emphasising the period from 1999–2010) South African biological control projects against individual invasive alien plant species, or against taxonomically- or functionally-related groups of species. Three of the papers deal with issues related to research and implementation of biological control, namely: regulations and risk assessment; mapping; and cost:benefit analyses. The concluding paper is a complete catalogue, with summary statistics and key references, of all the target weeds and of the insect, mite and pathogen species (and subsidiary taxa) that have been implicated in biological control efforts against invasive alien plants in South Africa since 1913. This compilation is the third in a series of accounts of all the biological control programmes against invasive alien plants that have been undertaken in South Africa: the first, produced in 1991, reviewed progress to that date and the next, published in 1999, was a review of progress from 1990–1998. A comparison of the contents of these three review volumes is given in tabular form. The 2011 compilation contains reports on 13 novel programmes, in the sense that they have not been previously reviewed. Eight of these projects have focused on incipient weeds, or on rapidly-emerging weed species or groups of species, that have only recently been targeted for biological control. The increased scope and commitment to weed biological control research in South Africa has been largely the consequence of the sustained support provided by the Working for Water Programme of the South African Department of Water Affairs, over the last 15 years.

In total, ten agent species have been released in South Africa for the biological control of ten invasive Australian Acacia species and Paraserianthes lophantha (Willd.) Nielsen (Mimosaceae). Besides a single fungal pathogen species which affects both reproductive and vegetative growth of its host plant, Acacia saligna (Labill.) H.L.Wendl., there are nine herbivorous insect species which predominantly suppress the reproductive output of their host plants. These include five seed-feeding weevil species, two flower-galling fly species and two bud-galling wasp species. An indigenous basidiomycete fungus, which causes die-back disease of Acacia cyclops A. Cunn. ex G. Don, has also been investigated. During the last ten years, considerable effort has been directed at searching for new agents in Australia and in collecting additional material to bolster populations of recently-established agents in South Africa. Concurrently, ongoing evaluation studies in South Africa have measured the dynamics of the introduced agents as well as their impact on the vigour and fecundity of their host plants and the extent to which their damage is reducing the density, distribution and invasiveness of the Acacia species. Progress with all of these projects is reviewed.

Ageratina adenophora (Spreng.) R.M.King & H.Rob. and Ageratina riparia (Regel) R.M.King & H.Rob. (Asteraceae: Eupatorieae), originally from Mexico, are invasive in many countries. These plants produce thousands of wind- and water-dispersed seeds which enable them to spread rapidly and invade stream banks and moist habitats in areas with high rainfall. Two biological control agents, a shoot-galling fly, Procecidochares utilis Stone (Diptera: Tephritidae), and a leaf-spot fungus, Passalora ageratinae Crous & A.R. Wood (Mycosphaerellales: Mycosphaerellaceae), were introduced against A. adenophora in South Africa in 1984 and 1987, respectively. Both established but their impact is considered insufficient. Exploratory trips to Mexico between 2007 and 2009 to search for additional agents on A. adenophora produced a gregarious leaf-feeding moth, Lophoceramica sp. (Lepidoptera: Noctuidae), a stem-boring moth, probably Eugnosta medioxima (Razowski) (Lepidoptera: Tortricidae), a leaf-mining beetle, Pentispa fairmairei (Chapuis) (Coleoptera: Chrysomelidae: Cassidinae), and a leaf-rust, Baeodromus eupatorii (Arthur) Arthur (Pucciniales: Pucciniosiraceae) all of which have been subjected to preliminary investigations. Following its success in Hawaii, the white smut fungus, Entyloma ageratinae R.W Barreto & H.C. Evans (Entylomatales: Entylomataceae), was introduced in 1989 to South Africa against A. riparia. Its impact has not been evaluated since its establishment in 1990 in South Africa. By 2009, however, A. riparia was rarely observed in the field and E. ageratinae was noted to be present over most of the range of the weed, providing circumstantial evidence that the weed has been brought under biological control by E. ageratinae in South Africa.

Madeira vine, Anredera cordifolia (Ten.) Steenis subsp. cordifolia (Basellaceae), is native to South America but has become invasive and problematic in many countries, including South Africa. Weedy vines are notoriously difficult to control through conventional mechanical and chemical means, so biological control of A. cordifolia in South Africa was initiated in 2003. No agents have yet been released against this plant in South Africa but exploratory observations on the life-history and host-specificity of two leaf-feeding beetles, Phenrica sp. (Coleoptera: Chrysomelidae) from Brazil and Plectonycha correntina Lacordaire (Coleoptera: Chrysomelidae: Chrysomelinae) from Argentina and Brazil, are reviewed here. Adults and larvae of both chrysomelids feed extensively on leaves and new growth of A. cordifolia, resulting in leaf and above-ground biomass reductions. The laboratory host-ranges of these potential agents seem acceptably narrow, with normal development restricted to the host plant. Adult feeding was recorded on other non-indigenous species within the Basellaceae, Portulacaceae and Talinaceae. The Phenrica sp. colony, being reared in quarantine, died out and re-collection has not been possible. Host-specificity studies are continuing on P. correntina.

Mexican poppies Argemone mexicana L. and Argemone ochroleuca Sweet subsp. ochroleuca (Papaveraceae) are annual herbs native to Central America (Mexico) that have become naturalized and weedy in many parts of the world, including South Africa. Both A. mexicana and A. ochroleuca colonize and persist in severely disturbed areas, such as cropping systems, along roadsides, railway lines and watercourses. They compete with, and possibly displace indigenous pioneer species, threatening biodiversity of riparian zones in particular. They are also toxic to animals and humans. Although control measures such as herbicides can be applied, their use in sensitive areas such as riparian zones can cause deleterious effects and therefore biological control is considered to be the most suitable and environmentally safe method to suppress these weeds. Accordingly, two species of flower- and fruit-feeding curculionid beetles provisionally identified as Conotrachelus cf. leucophaeatus Fâhraeus (Coleoptera: Curculionidae: Conotrachelini), and Sirocalodes cf. wickhami (Champion) (Curculionidae: Ceutorhynchini) were collected in Mexico in 2007 and in 2009 and brought to South Africa for evaluation as potential biological control agents. Preliminary host-specificity tests indicated that the beetles strongly prefer the target weeds to other plant species. They are highly damaging and have the potential to substantially reduce seed production and thereby curb the spread of the two Argemone species.

This review is a summary of developments that have contributed to the success of several biological control programmes against invasive cactus species (Cactaceae) that have been worked on in South Africa over the last 12 years. Six potential biological control agents have been identified for the control of Pereskia aculeata Mil. and molecular studies have identified the origin of the South African P. aculeata population. Host-specificity testing is now required for the three most promising of these agents. The successful biological control programme against Opuntia stricta (Haw.) Haw. has resulted in a change in management strategies against this weed in the Kruger National Park and the control of O. stricta is now almost entirely reliant on biological control. Taxonomic problems associated with the identification of Cylindropuntia fulgida var. fulgida (Engelm.) F.M.Knuth var. fulgida have been resolved and an appropriate cochineal insect (Hemiptera: Dactylopiidae) biotype has been released, resulting in substantial declines in Cyl. fulgida var. fulgida populations. A long-term monitoring programme has been initiated to evaluate the progress of this new cochineal insect biotype. The Harrisia mealybug, Hypogeococcus pungens Granara de Willink (Hemiptera: Pseudococcidae), which was originally released on Harrisia martinii (Labour.) Britton & Rose has been collected and redistributed onto Cereus jamacaru DC., where it reduces fruit production and leads to the death of both seedlings and large plants. Resolving taxonomic problems to ensure the correct identification of plant species and the most appropriate biological control biotypes have been key issues that have led to the successful control of several cactaceous weed species in South Africa.

A seed-feeding beetle, Sulcobruchus subsuturalis (Pic) (Coleoptera: Chrysomelidae: Bruchinae), was released in South Africa in 1999 as a biological control agent against the invasive, leguminous, scrambling shrub Caesalpinia decapetala (Roth) Alston (Fabaceae). Despite being easy to rear in the laboratory and having been released in large numbers (>350 000) and widely distributed at many field sites, the beetle remains scarce where present and has failed to persist at many of the original release sites. Although eggs are oviposited readily on loose seeds in dishes, the few eggs that were found at release sites in the field were always on seeds still attached to pods hanging on plants. High levels of predation and parasitism were recorded in the field, which may be hindering population expansion by the beetle. Clarity about the taxonomic status of S. subsuturalis, and uncertainty as to the centre of origin of the weed, have led to suspicions that C. decapetala may exist as several biotypes, and that the local variety may not be a suitable host for the form of S. subsuturalis that has been imported into South Africa. These uncertainties should be addressed, together with additional efforts to determine what is happening to the agent in the field. Other phytophagous species from different feeding-guilds need to be investigated as potential biological control agents.

Pompom weed, Campuloclinium macrocephalum (Less.) DC. (Asteraceae), is a South American invasive plant that was first recorded in South Africa in the early 1960s. In the 1980s, C. macrocephalum started slowly extending its range and in the 1990s and 2000s it entered a dramatic expansion phase. It invades grasslands, savannas and wetlands where it has a significant impact on biological diversity. Control of C. macrocephalum has, so far, been based on herbicides, as mechanical approaches were found to exacerbate infestations through disturbance. However, due to the extent of the invasion, the financial and environmental costs of treating all C. macrocephalum infestations with herbicides would be prohibitive. As a result, a biological control programme was initiated against the weed in 2003. Surveys conducted on C. macrocephalum in its native range, indicated that northern Argentina has the highest diversity of natural enemies associated with the plant. Three insect species, Zeale (=Adesmus) nigromaculatus Klug (Coleoptera: Cerambycidae), Liothrips tractabilis Mound & Pereyra (Thysanoptera: Thripidae) and Cochylis campuloclinium Brown (Lepidoptera: Tortricidae), and one pathogen, Puccinia eupatorii Dietel (Pucciniales: Pucciniaceae) were rated (based on damage, range and abundance) as having the most potential as biological control agents for C. macrocephalum. This paper is a review of the biology, host range and potential impacts of these agents, as well as the prospects for the control of C. macrocephalum in South Africa.

Balloon vine, Cardiospermum grandiflorum Sw. (Sapindaceae), originally from South and Central America and now invasive in South Africa, was one of five incipient or ‘emerging weeds’ targeted for biological control in 2003. In search of potential biological control agents, exploratory surveys were conducted in northern Argentina from 2005 to 2009. The surveys, which included plant species in the genus Cardiospermum and other native Sapindaceae, were aimed at determining the distribution and field host ranges of the natural enemies associated with C. grandiflorum. Eight phytophagous insect and two fungal pathogen species were associated with C. grandiflorum, four of which were introduced into quarantine in South Africa for further host-specificity testing. Based on the nature of the potential agents' damage, field distribution, abundance, field host range and the results of preliminary host-specificity tests, the seed-feeding weevil Cissoanthonomus tuberculipennis Hustache (Coleoptera: Curculionidae) and the fruit-galling midge Contarinia sp. (Diptera: Cecidomyiidae) were deemed to be the most promising insect agents. Also promising was the rust fungus Puccinia arechavaletae Speg. (Fucciniales: Fucciniaceae) which caused severe disease symptoms on South African C. grandiflorum. However, feeding on two congeners of C. grandiflorum, whose exact country of origin is disputed, has limited the number of agents that are suitable for release. To resolve this problem, phylogenetic studies are currently under way to verify the contention that both non-target Cardiospermum species are native to South America and not to Africa. If that proves to be true, then these and other agents would qualify for release against C. grandiflorum in South Africa. Although this is a very recent programme, prospects for success seem good.

In 2008, a field survey was conducted in northern Argentina to collect natural enemies of Cestrum species (Solanaceae) for use as biological control agents in South Africa. The rust fungus Uromyces cestri Bertero ex Mont. (Pucciniales: Pucciniaceae) was found on Cestrum parqui L'Hér. and imported into quarantine facilities in South Africa. No damaging pathogens were found on Cestrum laevigatum Schltdl. Preliminary host-range studies showed that U. cestri was able to infect and cause disease on C. parqui and on Cestrum elegans (Brongn. ex Neumann) Schltdl. in South Africa, and could have potential for the biological control of these species. The rust did not infect any of the other Cestrum species tested, and neither did it infect C. laevigatum which is the most problematic Cestrum species in South Africa.

Research initiated in 1988 on the biological control of the invasive Neotropical shrub Chromolaena odorata (L.) R.M.King & H.Rob. (Asteraceae) in South Africa is described in this review. The origin of the southern African C. odorata biotype has been determined as the Greater Antilles in the Caribbean. Regions of the Neotropics which are climatically similar to the area invaded by the weed in southern Africa have been identified, allowing for better climatic matching of potential biological control agents. Two insect agents, Pareuchaetes insulata (Walker) (Lepidoptera: Arctiidae), which was released in 2001, and Calycomyza eupatorivora Spencer (Diptera: Agromyzidae), released in 2003, have become established on C. odorata in South Africa, primarily in the wetter, coastal regions. While these agents have inflicted sporadic, localized damage on the weed, it is clear that their impact on C. odorata populations will be insufficient to effect adequate suppression of the weed throughout its invasive range in South Africa. Thus, research on a wide range of insect and pathogen species which have potential as biological control agents has been ongoing. Initial releases of a stem-boring weevil, Lixus aemulus Petri (Coleoptera: Curculionidae), have been made, and host-range testing of the shoot-tip borer Dichrorampha odorata Brown & Zachariades (Lepidoptera: Tortricidae) indicates that it is suitable for release. The root feeder Longitarsus sp. (Coleoptera: Chrysomelidae) was rejected because it was shown to have a wide host range. Four promising insect species are currently being investigated, namely the stem galler Conotrachelus reticulatus Champion (Coleoptera: Curculionidae), the stem borer Carmenta chromolaenae Eichlin (Lepidoptera: Sesiidae), the stem and root-crown borer Recchia parvula (Lane) (Coleoptera: Cerambycidae) and the shoot-tip borer Melanagromyza eupatoriella Spencer (Diptera: Agromyzidae). Sustained efforts have been made to collect and isolate pathogens from C. odorata in the Americas, but all pathogens either failed to produce symptoms or were insufficiently virulent on the southern African biotype of the target plant. Although considerable efforts and resources have been expended on research and implementation of biological control against C. odorata, the plant is not yet under any significant degree of biological control in South Africa and it continues to be a weed of national and international importance.

Hakea sericea Schrad. & J.C. Wendl. and Hakea gibbosa (Sm.) Cav. (Proteaceae), are small trees or shrubs that originate from Australia. Hakea sericea has become highly invasive and problematic in South Africa while H. gibbosa is less widespread and abundant but nevertheless problematic. Biological control against H. sericea started in 1970 with the release of two seed-attacking insects, a seed-feeding weevil, Erytenna consputa Pascoe (Coleoptera: Curculionidae), and a seed-moth, Carposina autologa Meyrick (Lepidoptera: Carposinidae). Both of these agents, together with an indigenous fungus, Colletotrichum acutatum J.H. Simmonds f.sp. hakeae Lubbe, Denman, P.F. Cannon, J.Z. Groenew., Lampr. & Crous (Incertae sedis: Glomerellaceae), and manual clearing have reduced the abundance, and possibly the invasiveness, of H. sericea, but large infestations still persist in the coastal mountains of the Cape Floral Region in the Western and Eastern Cape provinces of South Africa. The release in 1979 of a weevil, Cydmaea binotata Lea (Coleoptera: Curculionidae), which bores in the terminal shoots and young needles of H. sericea has had a negligible effect. To enhance the levels of biological control, two new agents, a stem-boring beetle, Aphanasium australe (Boisduval) (Coleoptera: Cerambycidae), and a flowerbud feeder, Dicomada rufa Blackburn (Coleoptera: Curculionidae), were released in 2001 and 2006, respectively. The focus in this review is on progress since 1999 with the biological control and management of H. sericea. Releases of E. consputa and A. australe on H. gibbosa have met with limited success, the reasons for which are also reviewed.

Recent progress in the nomenclature and genetics of the hybrid-complex ‘lantana’ is summarized as it pertains to sourcing the best-adapted natural enemies for its biological control. Reasons are given for viewing the whole array of invasive taxa within Lantana L. sect. Camara Cham. (Verbenaceae) as a syngameon, and for surveying natural enemies of camara-like Lantana entities between Florida and Uruguay. To improve the degree of biological control of lantana, additional agents have been selected, evaluated and found suitable for release in South Africa. The quarantine evaluation and current status of 30 candidate biological control agents obtained from the New World is summarized. Of these, seven were found to be suitable for release, according to given criteria, and two new agents, Aceria lantanae (Cook) (Acari: Eriophyidae) and Ophiomyia camarae Spencer (Diptera: Agromyzidae), are improving control of lantana in humid, frost-free areas. No significant non-target effects have been detected. Information on the distribution and abundance of 17 agents and lantanaassociated insects established in South Africa is presented: several are mainly coastal and they are scarce overall. Agent proliferation is constrained by a combination of climatic incompatibility, acquired natural enemies and, probably, the broad spectrum of allelochemicals present in the allopolyploid hybrids within the L. camara complex. In the case of lantana, biological control plays a subsidiary role in support of essential mechanicalplus-chemical control. Cost benefits justify the continued development of additional agents.

In South Africa, two imported insect species have been used in attempts to control invasive Australian myrtle trees, Leptospermum laevigatum (Gaertn.) F.Muell. (Myrtaceae): a bud-galling midge, Dasineura strobila Dorchin (Diptera: Cecidomyiidae), which was inadvertently introduced, possibly in the mid-1980s, and a leaf-mining moth, Aristaea (Parectopa) thalassias (Meyrick) (Lepidoptera: Gracillariidae), which was released in 1996. The latter agent attacks young leaves only and has no discernible impact on mature trees. The number of L. laevigatum buds on mature trees that are galled by D. strobila was monitored from 1994 until 2008. Initially the prognosis for biological control by D. strobila was extremely promising. However, the numbers of galls then declined sharply at most of the sites, on average to less than half of their previous peak levels. Gall-midge mortality, induced by native parasitoids, was very low initially, and, some years later, peaked at an average of only about 8 %. In 2004, predatory mites, mostly Pyemotes species (Trombidiformes: Pyemotidae), were discovered, killing an average of 27% (9.8–61.3%) of the D. strobila larvae and pupae in the galls, but their role in regulating populations of D. strobila has not been proven. A chemical exclusion experiment on seedlings showed that leaf damage by A. thalassias together with galling by D. strobila reduced the growth of young L. laevigatum plants by nearly 50%, but, again, the impact of the two agents in aggregate, on mature plants, is negligible. A gall-inducing scale insect is presently under consideration as a potential agent, and there are some other possible agents that might be useful, but, overall, the prospects for biological control of L. laevigatum do not appear to be good.

Leucaena leucocephala (Lam.) de Wit (Fabaceae) is a typical ‘conflict species’, possessing both useful and damaging attributes, that has become naturalized in several countries worldwide, following deliberate introductions for agroforestry. Considered one of the ‘World's 100 Worst Invaders’, the plant in South Africa is an incipient or ‘emerging weed’, with infestations mostly occurring in the eastern subtropical regions of the country. Deliberate biological control efforts have been confined to South Africa, although these have been opportunistic, unfunded and, given the plant's propensity for prolific seed production, have focused exclusively on the seed beetle, Acanthoscelides macrophthalmus (Schaeffer) (Chrysomelidae: Bruchinae). Following confirmation of host specificity, and after several low-intensity releases, the beetle has become widely established in KwaZulu-Natal, where releases were mostly made, but also in Gauteng, Mpumalanga and the North West provinces. A sap-sucking psyllid, Heteropsylla cubana Crawford (Psyllidae), was inadvertently introduced into South Africa, but has not had any impact on weed infestations. The biological control programme against L. leucocephala in South Africa is reviewed, including: (i) aspects of the target plant that are pertinent to its invasiveness and management; (ii) details pertaining to the two natural enemies that have featured so far; (iii) progress that has been achieved; and (iv) the direction of future research efforts.

The exotic vine Macfadyena unguis-cati (L.) A.H.Gentry (Bignoniaceae), cat's claw creeper, has become a significant threat to the biodiversity of a variety of sensitive ecosystems in South Africa. Owing to the nature of the infestations, as well as the difficulties and prohibitive costs associated with both mechanical and chemical controls, biological control is considered to be the most practical and sustainable means of successfully managing the weed in South Africa. The biological control programme against M. unguis-cati was initiated in 1996 and resulted in the release of Charidotis auroguttata Boheman (Coleoptera: Chrysomelidae: Cassidinae). Despite repeated releases, initial rates of establishment were low. Where successfully established, populations of the beetle have been slow to build-up, leading to only limited impact on the weed. Prompted by this lack of success, as well as the high potential for further spread of the weed, additional natural enemies were sought. Two lace bugs, Carvalhotingis visenda Drake & Hambleton, and Carvalhotingis hollandi Drake (Hemiptera: Tingidae), a leaf-mining beetle Hylaeogena (Hedwigiella) jureceki Obenberger (Coleoptera: Buprestidae), a leaf-tying moth Hypocosmia pyrochroma Jones (Lepidoptera: Pyralidae) and a seed-feeding weevil Apteromechus notatus (Hustache) (Coleoptera: Curculionidae) were subsequently imported into quarantine in South Africa for host-specificity testing. With the exception of A. notatus, all have been approved for release and are exhibiting promising initial rates of establishment and damage at a number of field localities. Impact studies have shown that cat's claw creeper is susceptible to sustained herbivore pressure.

The annual herbaceous plant, Parthenium hysterophorus L. (Asteraceae) (parthenium), has been a major weed of global significance for several decades, with wide-ranging impacts on agriculture, biodiversity conservation, and human and animal health. Despite this, in 2003, South Africa became the first African country and only the third country worldwide to implement a biological control programme against the weed. It seems that a suite of agents is needed to achieve effective biological control of parthenium under different environmental conditions and in different regions. The rust fungus, Puccinia abrupta Dietel & Holw. var. partheniicola (H.S. Jacks.) Parmelee (Pucciniales: Pucciniaceae), is already present in South Africa. Three agents have been imported and evaluated, namely the leaf rust fungus Puccinia xanthii Schwein. var. parthenii-hysterophorae Seier, H.C. Evans & Á. Romero (Pucciniales: Pucciniaceae), which was released in 2010, and both the leaf-feeding beetle Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae: Cassidinae) and the stem-boring weevil Listronotus setosipennis (Hustache) (Coleoptera: Curculionidae), for which permission to release is being sought. A stem-galling moth Epiblema strenuana (Walker) (Lepidoptera: Tortricidae), seed-feeding weevil Smicronyx lutulentus Dietz (Coleoptera: Curculionidae), and stem-boring moth Carmenta nr. ithacae (Beutenmüller) (Lepidoptera: Sesiidae) are also under consideration. Studies conducted in South Africa prior to the release of biological control agents, demonstrated an extensive, but highly variable, soil seed bank. In 2005, the South African biological control programme was extended to Ethiopia through an international cooperative programme. Parthenium has the potential to become more widespread and problematic in sub-Saharan Africa, and the implementation of biological control could assist in reducing this risk.

Nine Pinus species (Pinaceae) have become invasive plants in South Africa after being deliberately introduced and cultivated in commercial forests, for timber. A proposal to use biological control to contain the problem raised concerns among foresters who immediately identified a number of difficulties that could arise for the forestry industry if biological control agents were to be introduced. As a compromise, plans were made to target, initially at least, two pine species, Pinus pinaster Alton and Pinus halepensis Mill, that currently have no commercial value. A cone-feeding weevil from Portugal, Pissodes validirostris Gyllenhal (Coleoptera: Curculionidae), was identified as the most promising agent. Formerly regarded as a single species, extensive preparatory studies revealed that there are several different forms (perhaps a complex of sibling species) of P. validirostris each associated with different pine species in different regions of Europe. Screening tests in arboreta in France showed that the prospective agent was host-specific enough to be used with safety in South Africa. Despite this positive finding, the programme did not proceed much further because subsequent trials in quarantine in South Africa showed that damage caused by the adult weevils feeding on leader shoots of pines allowed ingress of pitch canker, Fusarium circinatum Nirenberg and O'Donnell (Hypocreales: Nectriaceae), an increasingly problematic pathogen in pine forests in South Africa. However, given the escalating negative consequences of pine tree invasions, especially in the Cape Floral Region, the question of whether or not this biological control programme should have been discontinued in 2009 remains open for debate and the opposing views on the subject are presented.

The biological control programme against Prosopis species (Fabaceae) (mesquite) in South Africa has reached a stage where the already-established agents, Algarobius prosopis (LeConte) and Neltumius arizonensis (Schaeffer) (both Coleoptera: Chrysomelidae: Bruchinae), are considered to be inadequate. Other potential agents have been identified, including nine beetle species, four moths and a gall midge. Of these, a straight-snouted weevil, Coelocephalapion gandolfoi Kissinger (Coleoptera: Brentidae: Apioninae), whose larvae attack seeds within green pods, is considered especially promising and has been subjected to host-range tests. The biology, ecology and host range of a flowerbud galler, Asphondylia prosopidis Cockerell (Diptera: Cecidomyiidae), have also been investigated. Some pathogens have been considered, as either classical biological control agents or as mycoherbicides. Ongoing debates about the relative value and costs of the trees continue to hamper progress with the planned escalation of biological control. Recent assessments show that the costs of mesquite will soon outweigh the benefits in most situations, opening opportunities to clear additional agent species for release. The results of studies since 1999 on the established and the prospective agents on mesquite are reviewed, while considering the issues that need to be addressed to enable the biological control programme to proceed.

Solanum mauritianum Scop. (Solanaceae), a fast-growing tree with a high reproductive capacity, threatens several commercial activities and natural habitats in the higher rainfall regions of South Africa. Biological control efforts spanning 26 years have previously been confined to South Africa, but have recently been extended to New Zealand. The weed is a particularly challenging target for biological control, largely because of its taxonomic relatedness to economically important and native plant species which resulted in the rejection or shelving of the majority of candidate agents tested thus far. Despite these problems, two insect agents, the sap-sucking Gargaphia decoris Drake (Hemiptera: Tingidae) and flowerbud-feeding Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), have been released in South Africa. Gargaphia decoris was first released in 1999 and has become established in several regions of the country. Although large outbreaks and extensive damage have been observed in the field, to date these have been erratic and insufficient to inflict meaningful damage on the weed populations. Anthonomus santacruzi was released in early 2009 and so far appears to have established at two sites in KwaZulu-Natal. This paper is a review of the biological control programme against S. mauritianum in South Africa, including (i) aspects of the weed that are pertinent to its invasiveness and management, (ii) the current status of the two prominent insect agents, and (iii) the direction of future research efforts.

Solanum sisymbriifolium Lam. is a weed of disturbed areas in South Africa, particularly in the high-elevation summer rainfall areas of the country. Despite the introduction of the South American leaf-feeding tortoise beetle, Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae: Cassidinae) in 1994, the weed has continued to spread. Although established in a number of regions, beetle populations appear to persist in relatively low numbers, inflicting minimal damage to the weed. Consequently, a number of variables have been investigated in order to explain this lack of efficacy, and in some cases, failure to establish. Gratiana spadicea populations in South Africa are under considerable stress both from abiotic and biotic sources. Population-limiting factors such as disturbance of overwintering sites, climatic incompatibility, and high rates of pupal parasitism translate into low numbers of the agent at the start of each growing season. Small early-season populations which are slow to build-up, coupled with asynchronous development of S. sisymbriifolium, limit the beetles' effectiveness and pre-empt any impact on the weeds' reproductive output. Consequently, G. spadicea alone is unlikely to control S. sisymbriifolium infestations in South Africa. The flower-feeding weevil Anthonomus sisymbrii Hustache (Coleoptera: Curculionidae: Anthonominae), may therefore warrant study as it could have the potential, if released, to curtail fruit production and further spread of S. sisymbriifolium.

Tecoma stans (L.) Juss ex Kunth var. stans (Bignoniaceae), known as yellow bells, was introduced into South Africa as an ornamental plant and now invades roadsides, urban open spaces, watercourses and rocky sites in the subtropical and tropical areas of six South African provinces, and neighbouring countries. Although deemed to be an ‘emerging weed’, Tecoma stans has considerable potential to extend its range because it is still common in South African gardens and its seeds are easily dispersed by wind. Mechanical and chemical control methods are not economically feasible as the plant tends to re-grow, thus requiring expensive follow-up treatments. Biological control research on T. stans has been ongoing since 2003, when pathogens were the focus as agents, with insects included since 2005. Five candidate agents have so far been tested in South Africa, with one, Clydonopteron sacculana Bosc (Lepidoptera: Pyralidae), deemed unsuitable for release, one, Prospodium transformans (Ellis & Everh.) Cummins (Pucciniales: Uropyxidaceae), released initially in November 2010, and another, Pseudonapomyza sp. (Diptera: Agromyzidae), currently awaiting approval for release by the regulatory authorities. One candidate agent, Mada polluta (Mulsant) (Coleoptera: Coccinellidae), is still under investigation in quarantine. The last potential agent, a root-feeding flea beetle, Dibolia sp. (Coleoptera: Chrysomelidae), was brought into South Africa but the culture did not establish in quarantine.

Starting in 2007, two weedy sunflower species, Tithonia rotundifolia (Mill.) S.F.Blake and Tithonia diversifolia (Hemsl.) A.Gray (Asteraceae: Heliantheae), were targeted for biological control in South Africa. Surveys conducted in their native range (Mexico) revealed that there were five potential biological control agents for T. rotundifolia, and three of these are currently undergoing host-specificity and performance evaluations in South Africa. Two leaf-feeding beetles, Zygogramma signatipennis (Stål) and Zygogramma piceicollis (Stål) (Coleoptera: Chrysomelidae), are the most promising biological control agents for T. rotundifolia: preliminary host-specificity trials suggest that they are adequately host-specific. The stem-boring beetle, Lixus fimbriolatus Boheman (Coleoptera: Curculionidae), is also highly damaging to T. rotundifolia, but its host range is yet to be determined. Two other stem-boring beetles, Canidia mexicana Thomson (Coleoptera: Cerambycidae) and Rhodobaenus auctus Chevrolat (Coleoptera: Curculionidae), have also been recorded on T. rotundifolia, and these will be considered for further testing if L. fimbriolatus is found to be unsuitable for release in South Africa. Only two insect species were imported as candidate agents on T. diversifolia, the leaf-feeding butterfly Chlosyne sp. (Lepidoptera: Nymphalidae), and an unidentified stem-boring moth (Lepidoptera: Tortricidae): the latter was tested in quarantine but rejected because it attacked several sunflower cultivars. Only one pathogen, Puccinia enceliae Dietel & Holw. (Uredinales: Pucciniaceae), was found that could potentially have been used as a biological control agent against the Tithonia species, but attempts to culture this rust were unsuccessful.

Biological control against water hyacinth, Eichhornia crassipes (C.Mart.) Solms (Pontederiaceae), salvinia, Salvinia molesta D.S.Mitch. (Salviniaceae), water lettuce, Pistia stratiotes L. (Araceae), parrot's feather, Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), and red water fern, Azolla filiculoides Lam. (Azollaceae) has been ongoing in South Africa since the release of the first biological control agent on water hyacinth in 1974. This review provides an account of progress for the period from 1999. Post-release evaluations over the last three years have shown that, with the exception of water hyacinth, all of these problematic aquatic plants have been suppressed effectively using classical biological control. In eutrophic water bodies at high elevations that experience cold winters, an integrated approach, that includes herbicide application and augmentive biological control, is required against water hyacinth. The grasshopper Cornops aquaticum (Brüner) (Orthoptera: Acrididae: Leptysminae) has recently been released as a new agent for water hyacinth, and Megamelus scutellaris Berg (Hemiptera: Delphacidae) and Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) are being considered for release on water hyacinth. The longterm management of alien aquatic plants in South Africa relies on the prevention of new introductions of aquatic plant species that could replace those that have been controlled, and, more importantly, on a reduction in nutrient levels in South Africa's aquatic ecosystems.

Historically, biological control efforts against aquatic plants in South Africa have focused on floating species, and as a result, there has been a dearth of research into the invasion and control of submerged macrophytes. With numerous submerged invasive species already established in South Africa, thriving horticultural and aquarium industries, nutrient-rich water systems, and a limited knowledge of the drivers of invasions of submerged macrophytes, South Africa is highly vulnerable to a second phase of aquatic plant problems. Experience gained in the U.S.A. on biological control against submerged weeds, such as hydrilla, Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae) and spiked/Eurasian watermilfoil, Myriophyllum spicatum L. (Haloragaceae), have provided South African researchers with the necessary foundation to initiate programmes against these weeds. Research in South Africa is currently focused on pre-release studies on the biological control of H. verticillata, using an undescribed fly, Hydrellia sp. (Diptera: Ephydridae) and a weevil, Bagous hydrillae O'Brien (Coleoptera: Curculionidae); and on M. spicatum using a North American weevil, Euhrychiopsis lecontei Dietz (Coleoptera: Curculionidae). Feasibility studies into biological control of some incipient submerged weeds are also being conducted, including Brazilian water weed, Egeria densa Planch. (Hydrocharitaceae), Canadian water weed, Elodea canadensis Mitch. (Hydrocharitaceae) and cabomba, Cabomba caroliniana A.Gray (Cabombaceae). Progress with, and potential constraints that may limit these programmes, are discussed.

The importation and release of biological control agents against invasive alien plants in South Africa are subject to regulation by the Department of Agriculture, Forestry and Fisheries (DAFF), under its Agricultural Pests Act, and by the Department of Environmental Affairs (DEA), initially under its Environment Conservation Act, subsequently under the National Environmental Management Act and eventually, as soon as the relevant regulations have been developed, under the National Environmental Management: Biodiversity Act. Peer review, both within South Africa, and with colleagues in other countries, has helped to ensure the integrity of the science and practice of weed biological control in South Africa. This paper traces the development of the regulatory system from the first weed biological control project in 1913, through a dispensation when importations and releases were authorized by DAFF only to a dual regulatory system involving two government departments. Inappropriate legislation, lack of knowledge about biological control amongst the relevant authorities and the costs of employing compulsory private consultants are some of the reasons for significant delays that have become a feature in the authorization of biological control agent releases. These delays have set back several control programmes. Holding agents in quarantine while awaiting decisions ties up expensive space and staff time and increases the risk of losing colonies through accidents or decreased genetic vigour. It seems likely that changes in legislation within DEA will streamline the regulatory process in the near future.

The Southern African Plant Invaders Atlas (SAPIA) is a mapping project, launched in 1994, to collate data on the distribution, abundance and habitat types of invasive alien plants in southern Africa. The SAPIA database is a computerized catalogue of some 70 000 locality records of more than 600 naturalized alien plant species. The database incorporates records gathered by about 560 participants, since 1994, and from roadside surveys by the author since 1979. Among its many uses, SAPIA can assist biological control programmes, in several ways. Information on the geographical distributions and ecological requirements of invasive plants in their introduced range can ensure that biological control agents are brought from comparable habitats in their country of origin so as to optimize their chances of establishment and efficacy. Early detection of new invaders and new foci of spread allows implementation of biological control at an early stage of invasion with the potential to pre-empt severe problems. In the longer term, SAPIA can provide an historical record of the distribution of invasive plants and could be used to monitor their rate of expansion or contraction before and after biological control. This review is a report on the development of and recent progress with the SAPIA project.

This paper provides a brief review of the environmental and economic costs of invasive alien plants in South Africa as a background to assessments of returns on investment in weed biological control. The understanding of impacts and their economic costs is far from perfect, but estimates indicate that some costs (of lost water, grazing and biodiversity) are currently about R6.5 billion per annum (about 0.3 % of South Africa's GDP of around R2000 billion: R7 = about US$1), and could rise to > 5 % of GDP if invasive plants are allowed to reach their full potential. By comparing the costs of biological control research and implementation to the benefits of restored ecosystem services, or avoided costs, and avoided ongoing control costs, biological control has been shown to be extremely beneficial in economic terms: estimated benefit:cost ratios ranged from 8:1 up to 3726:1. Currently, spending on biological control is far lower than on other forms of control (about 5 % and 14 % of that spent on mechanical and chemical control, respectively), despite the significantly better returns on investment from biological control. In aggregate these assessments indicate that higher levels of spending on biological control research would generate extremely attractive returns on investment.

This catalogue provides a comprehensive record of the 284 entities of organisms (insect, mite and pathogen species, or biotypes thereof) that have featured in biological control of invasive alien plants (weeds) in South Africa, since 1913. Fourteen of these entities are native species, or foreign species that have, by some unknown means, entered the country, while the remainder were intentionally imported specifically for biological control. The majority (237 of 284, i.e. 83 %) are phytophagous insects, the balance being made up of five species of mites (Acari) and 42 entities of plant-pathogens. The catalogue comprises the names of each of the target weeds, their origin, and an assessment of the degree of control that has been achieved with biological control, together with names and details (feeding guild, date released where applicable, current status and extent of damage inflicted) for each of the agents. Key references are provided. Of the 270 entities that were introduced into quarantine and tested for host specificity: 106 (39 %) were eventually released as biological control agents; 16 % are still under investigation; approximately 24 % were rejected by researchers because of doubts about their safety or efficacy; and 21 % have been shelved pending possible further study. Two of the pathogen species were developed as mycoherbicides. Seventy-five (71 %) of the 106 agents that were released in South Africa have become established on 48 invasive alien plant species, in 14 plant families. According to a rating system that has been widely adopted since 1999, and slightly amended in this account, approximately 21 % of the weed species on which biological control agents are established have been completely controlled, and another 38 % are under a substantial degree of control.