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Distribution and impact of the Asian seed beetle, Megabruchidius tonkineus (Pic, 1904)(Coleoptera: Chrysomelidae: Bruchinae) on Gleditsia triacanthos L. seeds in South Africa

  • Authors: Salgado, Sara E , Martin, Grant D
  • Date: 2023
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/452266 , vital:75116 , http://dx.doi.org/10.17159/2254-8854/2023/a13386
  • Description: Honey locust, Gleditsia triacanthos (Fabaceae) is a fast-growing deciduous tree native to North America. The tree has been introduced worldwide and has become invasive in South Africa. In 2017, it was listed as one of the nine fastest-spreading weeds in South Africa. Once established, it competes with and displaces indigenous species and dense stands can significantly reduce stream flow. The Asian seed-feeding bruchid, Megabruchidius tonkineus (Coleoptera: Chrysomelidae: Bruchinae) was introduced into South Africa and has subsequently taken honey locust as a host plant. The beetle damages honey locust seeds and is therefore considered a biological control agent, despite no host-specificity or impact studies having been conducted. This study shows that M. tonkineus has established across the entire G. triacanthos population range in South Africa, damaging approximately 9% of seeds. Laboratory studies show that M. tonkineus completes its larval development in the seeds of G. triacanthos in about 66.80±0.69 SE days before emerging. This study is the first to describe the distribution and impact of this alien insect in South Africa.
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  • Date Issued: 2023

Distribution and impact of the native South African wasp, Megastigmus transvaalensis (Hussey, 1956)(Hymenoptera: Torymidae) on the invasive Schinus terebinthifolia Raddi (Anacardiaceae) in South Africa

  • Authors: Mangenlele, Nwabisa L , Martin, Grant D
  • Date: 2023
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/416841 , vital:71390 , xlink:href="https://hdl.handle.net/10520/ejc-ento_v31_n1_a12"
  • Description: Schinus terebinthifolia Raddi (Anacardiaceae) (Brazilian pepper tree) is a tree native to subtropical South America that was introduced into South Africa as an ornamental plant. Globally, it is regarded as one of the world’s worst invasive trees. In South Africa the tree has acquired a native seed-feeding wasp, Megastigmus transvaalensis (Hussey, 1956) (Hymenoptera: Torymidae). The wasp’s native hosts are from the Searsia F.A. Barkley genus (Anacardiaceae), but it has expanded its host range to form a new association with both S. terebinthifolia and its close relative Schinus molle L. (Anacardiaceae). In order to quantify the seed predation by M. transvaalensis on S. terebinthifolia seeds, tree populations were surveyed across the Eastern Cape and KwaZulu-Natal provinces. The wasp was present at 99% of the S. terebinthifolia populations with an average of 22% of the seeds being destroyed. In the Eastern Cape province, the highest seed damage occurred at the start of the winter months, when about 35% of seeds were damaged. This fell to less than 12% in spring and summer when the plants were flowering. Megastigmus transvaalensis was found at nearly all the S. terebinthifolia populations in South Africa, but due to the limited number of predated seeds it is unlikely to reduce population sizes or curb the spread of the invasive alien tree in South Africa.
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  • Date Issued: 2023

Sample size assessments for thermal physiology studies: An R package and R Shiny application

  • Authors: van Steenderen, Clarke J M , Sutton, Guy F , Owen, Candice A , Martin, Grant D , Coetzee, Julie A
  • Date: 2023
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/444455 , vital:74242 , https://doi.org/10.1111/phen.12416
  • Description: Required sample sizes for a study need to be carefully assessed to account for logistics, cost, ethics and statistical rigour. For example, many studies have shown that methodological variations can impact the critical thermal limits (CTLs) recorded for a species, although studies on the impact of sample size on these measures are lacking. Here, we present ThermalSampleR; an R CRAN package and Shiny application that can assist researchers in determining when adequate sample sizes have been reached for their data. The method is particularly useful because it is not taxon specific. The Shiny application offers a user‐friendly interface equivalent to the package for users not familiar with R programming. ThermalSampleR is accompanied by an in‐built example dataset, which we use to guide the user through the workflow with a fully worked tutorial.
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  • Date Issued: 2023

The thermal physiology of Lysathia sp.(Coleoptera: Chrysomelidae), a biocontrol agent of parrot’s feather in South Africa, supports its success

  • Authors: Goddard, Matthew , Owen, Candice A , Martin, Grant D , Coetzee, Julie A
  • Date: 2022
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/417806 , vital:71487 , xlink:href="https://doi.org/10.1080/09583157.2022.2054949"
  • Description: The establishment success of biocontrol agents originating from tropical regions is often limited by climate when introduced in temperate regions. However, the flea beetle, Lysathia sp. (Coleoptera: Chrysomelidae), a biocontrol agent of Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae) in South Africa, is an effective agent in regions where other biocontrol agents of tropical aquatic weeds have failed due to winter-induced mortality. The development (degree-day model) and thermal tolerance (critical thermal minimum/maximum [CTmin/max] and lower/upper lethal limits [LLT/ULT50]) of Lysathia sp. were investigated to explain this success. The model predicted that Lysathia sp. could complete 6 to 12 generations per year in the colder regions of the country. The lower threshold for development (t0) was 13.0 °C and thermal constant (K) was 222.4 days, which is considerably lower than the K values of other biocontrol agents of aquatic weeds in South Africa. This suggests that above the temperature threshold, Lysathia sp. can develop faster than those other species and complete multiple life cycles in the cooler winter months, allowing for rapid population growth and thus improving M. aquaticum control. Furthermore, the CTmin of Lysathia sp. was 2.3 ± 0.2 °C and the CTmax was 49.0 ± 0.5 °C. The LLT50 was calculated as ∼ −7.0 °C and the ULT50 as ∼ 43.0 °C. These wide tolerance ranges and survival below freezing show why Lysathia sp. has established at cool sites and suggest that it may be a suitable agent for other cold countries invaded by M. aquaticum.
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  • Date Issued: 2022

A review of the biocontrol programmes against aquatic weeds in South Africa

  • Authors: Coetzee, Julie A , Bownes, Angela , Martin, Grant D , Miller, Benjamin E , Smith, Rosalie , Weyl, Philip S R , Hill, Martin P
  • Date: 2021
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/406965 , vital:70326 , xlink:href="https://hdl.handle.net/10520/ejc-ento_v29_n3_a18"
  • Description: Biological control (biocontrol) against invasive macrophytes is one of the longest standing programmes in South Africa, initiated in the 1970s against water hyacinth, Pontederia crassipes Mart. (Pontederiaceae). Since then, 15 agent species (13 insects, one mite and one pathogen) have been released against six weeds, most of which are floating macrophytes, with excellent levels of success. The release of the water hyacinth planthopper Megamelus scutellaris Berg (Hemiptera: Delphacidae) in particular, has improved biocontrol prospects for water hyacinth since 2018. In the last decade, however, a new suite of submerged and rooted emergent invasive macrophytes has been targeted. The first release against a submerged macrophyte in South Africa, and the first release against Brazilian waterweed, Egeria densa Planch. (Hydrocharitaceae), anywhere in the world, was achieved with the release of a leafmining fly, Hydrellia egeriae Rodrigues-Júnior, Mathis and Hauser (Diptera: Ephydridae). Yellow flag, Iris pseudacorus L. (Iridaceae) and Mexican waterlily, Nymphaea mexicana Zucc. (Nymphaeaceae), have also been targeted for biocontrol for the first time worldwide, and are in the early stages of agent development. Post-release evaluations, long term monitoring and controlled experiments have highlighted the need for a more holistic approach to managing aquatic invasive plants in South Africa, whose presence is largely driven by eutrophication, resulting in regime shifts between floating and submerged invaded states.
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  • Date Issued: 2021

An introduction to the fourth decadal review of biological control of invasive alien plants in South Africa (2011–2020)

  • Authors: Paterson, Iain D , den Breeyen, Alana , Martin, Grant D , Olckers, Tamryn
  • Date: 2021
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/413387 , vital:71031 , xlink:href="https://hdl.handle.net/10520/ejc-ento_v29_n3_a2"
  • Description: This special issue is the fourth decadal review of biological control of invasive alien plants (biocontrol of weeds) in South Africa, following those published in 1991, 1999 and 2011. Including this introduction, there are 24 papers covering the weed biocontrol programmes, or important developments in the science and practice, from the period 2011-2020. Seventy-two target weed species are covered, including 25 species on which projects were initiated during the past decade. Developments in regulations, mass-rearing and implementation, and community engagement are also reviewed. An updated catalogue of agents released, rejected and under consideration is presented and reflects the most recent methods of quantifying success in weed biocontrol. Key events over the last decade include the hosting of the XIV International Symposium on Biological Control of Weeds to celebrate 100 years of weed biocontrol in South Africa, as well as the establishment of the Centre for Biological Control at Rhodes University. The science and practice of weed biocontrol has expanded significantly in the past decade, with growth in the number of researchers and practitioners, increased funding, and an increased number of scholarly outputs. Unlike many other countries in the world, South Africa has largely avoided constraints due to restrictive and risk averse legislation and bureaucracy, and has continued to release new biocontrol agents at a similar rate to that in previous years. Much of the success of weed biocontrol in South Africa is due to the sustained and increasing support of the Natural Resource Management Programme of the Department of Forestry, Fisheries and the Environment (Working for Water Programme). However, gaps in funding, where no funds are available for months at a time, are a major concern as the weed biocontrol community loses human capital in these periods, and research programmes suffer significant set-backs. Weed biocontrol is an essential component of South Africa’s strategy to reduce the negative impacts of invasive alien plants and has contributed significantly towards the protection of the country’s ecosystems, indigenous biodiversity, water security, agricultural productivity, and society in general. If the trend of increasing support for weed biocontrol in South Africa continues, we can expect that the benefits for the country at large will increase substantially in the future.
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  • Date Issued: 2021

Biological control of South African plants that are invasive elsewhere in the world: A review of earlier and current programmes

  • Authors: Olckers, Terence , Coetzee, Julie A , Egli, Daniella , Martin, Grant D , Paterson, Iain D , Sutton, Guy F , Wood, Alan R
  • Date: 2021
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/414336 , vital:71137 , xlink:href="https://hdl.handle.net/10520/ejc-ento_v29_n3_a21"
  • Description: South Africa supports a rich floral diversity, with 21 643 native plant taxa that include a high proportion (76.3%) of endemic species, and many of these favoured as ornamentals, both locally and globally. Consequently, South Africa has contributed substantially to global plant invasions, with 1093 native taxa (5% of all species) naturalized in other countries. At least 80 taxa are invasive in natural or semi-natural ecosystems elsewhere, while an additional 132 taxa are potentially invasive. Of the global naturalized flora, 8.2% originate from South Africa and largely comprise species of Poaceae, Asteraceae, Iridaceae and Fabaceae. Australia, in particular, but also Europe and North America are major recipients of South African weeds. However, few countries have targeted South African plants for biological control (biocontrol), with most efforts undertaken by Australia. Previous and current targets have involved only 26 species with 17 agents (15 insects, one mite and one rust fungus) of South African origin released on five target species in Australia and the United States of America. South Africa’s history of weed biocontrol, together with a large cohort of active scientists, is currently facilitating several internationally funded programmes targeting invasive plants of South African origin. In particular, the recently inaugurated Centre for Biological Control at Rhodes University and the University of KwaZulu-Natal have provided the impetus for novel efforts on five new target species and renewed efforts on four previously targeted species. In this contribution, we review the history of earlier biocontrol programmes against weeds of South African origin and the status of projects currently in progress in South Africa.
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  • Date Issued: 2021

Prospects for the biological control of Northern Temperate Weeds in South Africa

  • Authors: Martin, Grant D
  • Date: 2021
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/414478 , vital:71151 , xlink:href="https://hdl.handle.net/10520/ejc-ento_v29_n3_a10"
  • Description: The Northern Temperate Weeds programme is a novel biological control (biocontrol) programme started in 2017, with the aim of reducing the impacts of northern temperate weeds that are common, widespread and problematic in the high elevation grasslands of South Africa. As these regions are the most important systems for water security, providing nearly 50% of all water run-off, it is surprising that these species were not targeted for biocontrol previously. Thus far, research has focused on biocontrol feasibility as well as ecological and socio-economic impact studies on several northern temperate weeds, including Pyracantha angustifolia (Franch.) C.K.Schneid, Rosa rubiginosa L., Cotoneaster spp., Rubus spp., (all Rosaceae) and Salix spp. (Salicaceae). In addition, research conducted in the USA and Europe on the natural enemies associated with two of these species, Robinia pseudoacacia L. and Gleditsia triacanthos L. (both Fabaceae and native to the USA), 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 R. pseudoacacia, using the leaf miner Odontota dorsalis Thunberg (Coleoptera: Chrysomelidae) and the black locust midge Obolodiplosis robiniae Haldeman (Diptera: Cecidomyiidae), and on G. triacanthos, using a seed bruchid, Amblycerus robiniae F. (Coleoptera: Chrysomelidae). Progress with these programmes and potential constraints that may limit success, are discussed.
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  • Date Issued: 2021

Three new biological control programmes for South Africa: Brazilian pepper, Tamarix and Tradescantia

  • Authors: Byrne, Marcus J , Mayonde, Samalesu , Venter, Nic , Chidawanyika, Frank , Zachariades, Costas , Martin, Grant D
  • Date: 2021
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/414490 , vital:71152 , xlink:href="https://hdl.handle.net/10520/ejc-cristal-v10-n1-a7"
  • Description: Three weed biological control (biocontrol) programmes are described, all of which are considered to be ‘transfer projects’ that were initiated elsewhere, and on which South Africa has piggybacked its biocontrol efforts. Using knowledge and expertise from international collaborators, South African weed researchers are following a long tradition of transfer projects, which has been a largely successful and practical approach to biocontrol. Two Brazilian weeds, the Brazilian pepper tree Schinus terebinthifolia and the spiderwort Tradescantia fluminensis are being targeted, along with the Old-World trees Tamarix ramosissima and T. chinensis. The potential biocontrol agents are described and ranked for the two trees according to what has been discovered elsewhere, while the agent already released against T. fluminensis is rated (as poor), and other potential agents are considered. The addition of molecular techniques, climate matching and remote sensing in transfer projects can increase the chance of successful biocontrol and the inclusion of these techniques in the three new programmes is discussed. Transfer projects are a cost-effective and pragmatic way to pick winning biocontrol programmes.
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  • Date Issued: 2021

Climate modelling suggests a review of the legal status of Brazilian pepper Schinus terebinthifolia in South Africa is required:

  • Authors: Martin, Grant D , Magengelele, Nwabisa L , Paterson, Iain D , Sutton, Guy F
  • Date: 2020
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/148606 , vital:38754 , https://doi.org/10.1016/j.sajb.2020.04.019
  • Description: Brazilian pepper (Schinus terebinthifolia) is a tree native to subtropical South America that was introduced into South Africa in the early 1900s as an ornamental plant. The tree has since escaped cultivation and has invaded ruderal and pristine habitats along the eastern coast of South Africa. Brazilian Pepper is also one of the most problematic invasive alien plants in Florida, USA. We modelled the climatically suitable area for this species in South Africa using MaxEnt, with five distinct datasets: incorporating both the native and the invaded range of the species, as well as different backgrounds.
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  • Date Issued: 2020

Genetic diversity and morphological variation in African boxthorn (Lycium ferocissimum)–characterising the target weed for biological control

  • Authors: McCulloch, Graham A , Mauda, Evans V , Chari, Lenin D , Martin, Grant D , Gurdasani, Komal , Morin, L , Walter, Grenville H , Raghu, S
  • Date: 2020
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/423474 , vital:72064 , xlink:href="https://doi.org/10.1016/j.biocontrol.2020.104206"
  • Description: Lycium ferocissimum (African boxthorn) is a Weed of National Significance in Australia. Biological control may have potential to manage this weed, but taxonomic uncertainty needs to be addressed first to facilitate searches for potential agents. We sampled putative L. ferocissimum (i.e. tentatively identified morphologically in the field) across its native range in South Africa and introduced range in Australia. Morphometric and genetic analyses were conducted to confirm the species identity of these samples, and to assess morphological and genetic variation across both ranges. All samples collected in Australia were confirmed as L. ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L. ferocissimum across both South Africa and Australia was low, with no evidence of genetic structure. One of the two common chloroplast haplotypes found across Australia was found at only two sites in South Africa, both near Cape Town, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa putatively identified in the field as L. ferocissimum were genetically characterised as different (unidentified) Lycium species. Our morphometric analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L. ferocissimum, and thus morphological identification of the latter species in its native range may remain problematic. To ensure the correct Lycium species is surveyed for candidate biological control agents we suggest that individuals should be permanently tagged and putative morphological determinations supplemented with genetic analyses to confirm species identity.
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  • Date Issued: 2020

Insect herbivores associated with Lycium ferocissimum (Solanaceae) in South Africa and their potential as biological control agents in Australia

  • Authors: Chari, Lenin D , Mauda, EV , Martin, Grant D , Raghu, S
  • Date: 2020
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/407035 , vital:70331 , xlink:href="https://hdl.handle.net/10520/EJC-203b8dbc7b"
  • Description: Lycium ferocissimum Miers (Solanaceae) is an indigenous shrub in South Africa but has become invasive in several countries including Australia, where chemical and mechanical control methods have proved costly and unsustainable. In Australia, biological control is being considered as a management option, but the herbivorous insects associated with the plant in its native range are not well known. The aim of this study was to survey the phytophagous insects associated with L. ferocissimum in South Africa and prioritise promising biological control agents. In South Africa, the plant occurs in two geographically distinct areas, the Eastern and Western Cape provinces. Surveys for phytophagous insects on L. ferocissimum were carried out repeatedly over a two-year period in these two regions. The number of insect species found in the Eastern Cape Province (55) was higher than that in the WesternCapeProvince (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinellidae) and the leaf-mining weevil Neoplatygaster serietuberculata Gyllenhal (Curculionidae).
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  • Date Issued: 2020

Invasive alien aquatic plants in South African freshwater ecosystems:

  • Authors: Hill, Martin P , Coetzee, Julie A , Martin, Grant D , Smith, Rosali , Strange, Emily F
  • Date: 2020
  • Language: English
  • Type: text , book
  • Identifier: http://hdl.handle.net/10962/176271 , vital:42680 , ISBN 978-3-030-32394-3 , 10.1007/978-3-030-32394-3
  • Description: South Africa has a long history of managing the establishment and spread of invasive fioating macrophytes. The past thirty years of research and the implementation of nation-wide biological and integrated control programmes has led to widespread control of these species in many degraded freshwater ecosystems. Such initiatives are aimed at restoring access to potable freshwater and maintaining native biodiversity.
  • Full Text: false
  • Date Issued: 2020

More than a century of biological control against invasive alien plants in South Africa: a synoptic view of what has been accomplished

The establishment and rapid spread of Sagittaria Platyphylla in South Africa:

  • Authors: Ndlovu, Mpilonhle S , Coetzee, Julie A , Nxumalo, Menzi M , Lalla, Reshnee , Shabalala, Ntombifuthi , Martin, Grant D
  • Date: 2020
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/149788 , vital:38884 , https://doi.org/10.3390/w12051472
  • Description: Sagittaria platyphylla Engelm. (Alismataceae) is a freshwater aquatic macrophyte that has become an important invasive weed in freshwater systems in South Africa, New Zealand, Australia, and recently China. In South Africa, due to its rapid increase in distribution and ineffective control options, it is recognised as one of the country’s worst invasive aquatic alien plants. In this paper, we investigate the spread of the plant since its first detection in 2008, and the management strategies currently carried out against it. Despite early detection and rapid response programmes, which included chemical and mechanical control measures, the plant was able to spread both within and between sites, increasing from just one site in 2008 to 72 by 2019. Once introduced into a lotic system, the plant was able to spread rapidly, in some cases up to 120 km within 6 years, with an average of 10 km per year. The plant was successfully extirpated at some sites, however, due to the failure of chemical and mechanical control, biological control is currently being considered as a potential control option.
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  • Date Issued: 2020

Addressing geographical bias: A review of Robinia pseudoacacia (black locust) in the Southern Hemisphere

  • Authors: Martin, Grant D
  • Date: 2019
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/423937 , vital:72107 , xlink:href="https://doi.org/10.1016/j.sajb.2019.08.01"
  • Description: Robinia pseudoacacia (black locust) is a medium-sized deciduous tree, native to the Southeastern United States. Due to a number of beneficial attributes, it has been widely planted and become naturalised in several countries. It has one of the largest distributions in Europe of any introduced plant and has increased its distribution into a number of Southern Hemisphere countries. In its introduced range, the species exhibits a number of invasive tendencies, which result in negative environmental and economic impacts. This review presents information on aspects of the plant's biology and ecology with emphasis on its status in the Southern Hemisphere. Topics covered include taxonomy, morphological attributes, distributions, habitats, relationships with other species, growth and development, reproduction, hybridisation, population dynamics, uses, toxicity and the invasive status of the plant in Southern Hemisphere countries This manuscript also provides insights into management options including biological control, which has never been intentionally implemented against this species.
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  • Date Issued: 2019

Could enemy release explain invasion success of Sagittaria platyphylla in Australia and South Africa?.

  • Authors: Kwong, Raelene M , Sagliocco, Jean Louis , Harms, Nathan E , Butler, Kym L , Martin, Grant D , Green, Peter T
  • Date: 2019
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/76881 , vital:30633 , https://doi.org/10.1016/j.aquabot.2018.11.011
  • Description: Sagittaria platyphylla (delta arrowhead) is an emergent aquatic macrophyte native to southeastern United States of America that has been introduced into Australia and South Africa as an ornamental pond and aquarium plant. Compared to plants in the native range, S. platyphylla in the introduced range have greater reproductive capacity and form extensive infestations that dominate shallow waterbodies. One explanation for the invasive success of S. platyphylla in introduced countries is that plants are devoid of biotic pressures that would regulate population abundance in their native range (the enemy release hypothesis). We previously reported on field surveys that documented the number of pathogens and insect herbivores associated with S. platyphylla in native and introduced ranges. Here, we quantify the damage caused by these natural enemies to S. platyphylla in the two ranges. As predicted, damage to plants caused by pathogens and insect herbivores was much greater in the native than the introduced range at both the plant and population level. In introduced regions herbivory was low (less than 10%) in every plant part, while in North America insect damage to fruiting heads was 46% (of fruiting heads attacked), damage to leaves was between 33 to 57%, and internal herbivore damage to petioles and the inflorescence scapes was 56% and 43% respectively. Pathogen damage to leaves was between 39 to 57% of leaves per plant affected, compared to 9% in Australia and 8% in South Africa. This lack of biotic resistance from herbivores and disease may have facilitated S. platyphylla invasion in Australia and South Africa.
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  • Date Issued: 2019

Biological control of Salvinia molesta in South Africa revisited

  • Authors: Martin, Grant D , Coetzee, Julie A , Weyl, Philip S R , Parkinson, Matthew C , Hill, Martin P
  • Date: 2018
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/103878 , vital:32318 , https://doi.org/10.1016/j.biocontrol.2018.06.011
  • Description: The aquatic weed Salvinia molesta D.S. Mitch. (Salviniaceae) was first recorded in South Africa in the early 1900s, and by the 1960s was regarded as one of South Africa’s worst aquatic weeds. Following the release of the weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) in 1985, the weed is now considered under successful biological control. However, the post-release evaluation of this biological control programme has been ad hoc, therefore, to assess the efficacy of the agent, annual quantitative surveys of South African freshwater systems have been undertaken since 2008. Over the last ten years, of the 57 S. molesta sites visited annually in South Africa, the weevil has established at all of them. Eighteen sites are under successful biological control, where the weed no longer poses a threat to the system and 19 are under substantial biological control, where biological control has reduced the impact of the weed. Since 2008, the average percentage weed cover at sites has declined significantly from 51–100% cover to 0–5% cover in 2017 (R2 = 0.78; P < 0.05). Observations of site-specific characteristics suggest that biological control is most effective at small sites and more difficult at larger and shaded sites. Our findings show that S. molesta remains under good biological control in South Africa, however, some sites require intermittent strategic management, such as augmentative releases of C. salviniae.
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  • Date Issued: 2018

Invaded habitat incompatibility affects the suitability of the potential biological control agent Listronotus sordidus for Sagittaria platyphylla in South Africa

  • Authors: Martin, Grant D , Coetzee, Julie A , Lloyd, Melissa , Nombewu, Sinoxolo E , Ndlovu, Mpilonhle S , Kwong, Raelene M
  • Date: 2018
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/103926 , vital:32323 , https://doi.org/10.1080/09583157.2018.1460314
  • Description: Sagittaria platyphylla (Engelmann) J.G. Smith (Alismataceae) was first recorded in South Africa in 2008 and is considered to be an emerging weed with naturalised populations occurring throughout the country. A biological control programme was initiated in Australia and surveys conducted between 2010 and 2012 yielded potential agents, including the crown feeding weevil, Listronotus sordidus Gyllenhal (Coleoptera: Curculionidae). The potential of L. sordidus as a candidate biological control agent against S. platyphylla in South Africa was examined. Although adult feeding was recorded on a number of plant species, oviposition and larval development indicated a narrow host range restricted to the Alismataceae. In South Africa, S. platyphylla populations are primarily found in inundated systems. However, laboratory studies showed that L. sordidus did not oviposit on inundated plants, potentially nullifying the impact of the insect on South African populations. It is suggested that even though L. sordidus is a damaging, specific agent, its limited impact on inundated plant populations in South Africa does not justify the inherent risk associated with the release of a biological control agent.
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  • Date Issued: 2018

Plant–herbivore–parasitoid interactions in an experimental freshwater tritrophic system: higher trophic levels modify competitive interactions between invasive macrophytes

  • Authors: Martin, Grant D , Coetzee, Julie A , Compton, Stephen G
  • Date: 2018
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/125686 , vital:35808 , https://doi.org/10.1007/s10750-017-341
  • Description: Natural enemies are known to modify competitive hierarchies among terrestrial plants. Here we examine whether the same applies to freshwatersystems. Lagarosiphon major (Hydrocharitaceae) is a submerged aquatic macrophyte, indigenous to South Africa. Outside its native range, it outcompetes with indigenous submerged species and degrades aquatic habitats. Hydrellia lagarosiphon (Diptera: Ephydridae) is the most abundant and ubiquitous herbivore associated with L. major in South Africa and is a potential biological control agent elsewhere. Chaenusa anervata (Hymenoptera: Braconidae: Alysiinae) is its main parasitoid. We generated an experimental system involving one, two or three trophic levels to monitor variation in the competitive ability of L. major relative to that of Myriophyllum spicatum (Haloragaceae), a second submerged macrophyte that can also be invasive. Using inverse linear models to monitor competition, we found that herbivory by H. lagarosiphon greatly reduced the competitive ability of L. major. Addition of the wasp at typical field densities halved the impact of herbivory and reestablished the competitive advantage of L. major. Our results demonstrate how multitrophic interactions modify relative competitive abilities among aquatic plants, emphasize the significance of higher tropic levels in these systems and illustrate how parasitoids can reduce the effectiveness of insects released as biocontrol agents.
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  • Date Issued: 2018
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