African Entomology - Volume 19, Issue 1, 2011
Volumes & issues
Volume 19, Issue 1, 2011
Biological control of dense-thorned bitter apple, Solanum sisymbriifolium Lam. (Solanaceae), in South AfricaSource: African Entomology 19, pp 427 –433 (2011)More Less
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.
Potential agents for the biological control of Tecoma stans (L.) Juss ex Kunth var. stans (Bignoniaceae) in South AfricaSource: African Entomology 19, pp 434 –442 (2011)More Less
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.
Prospective agents for the biological control of Tithonia rotundifolia (Mill.) S.F. Blake and Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) in South AfricaSource: African Entomology 19, pp 443 –450 (2011)More Less
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.
A review of the biological control programmes on Eichhornia crassipes (C.Mart.) Solms (Pontederiaceae), Salvinia molesta D.S. Mitch. (Salviniaceae), Pistia stratiotes L. (Araceae), Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae) and Azolla filiculoides Lam. (Azollaceae) in South AfricaSource: African Entomology 19, pp 451 –468 (2011)More Less
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.
Source: African Entomology 19, pp 469 –487 (2011)More Less
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.
Regulation and risk assessment for importations and releases of biological control agents against invasive alien plants in South AfricaSource: African Entomology 19, pp 488 –497 (2011)More Less
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.
Mapping of invasive alien plants : the contribution of the Southern African Plant Invaders Atlas (SAPIA) to biological weed controlAuthor L. HendersonSource: African Entomology 19, pp 498 –503 (2011)More Less
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.
Source: African Entomology 19, pp 504 –514 (2011)More Less
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.
A catalogue of the insects, mites and pathogens that have been used or rejected, or are under consideration, for the biological control of invasive alien plants in South AfricaAuthor H. KleinSource: African Entomology 19, pp 515 –549 (2011)More Less
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.