Nutrient-mediated effects on Cornops aquaticum Brüner (Orthoptera: Acrididae), a potential biological control agent of water hyacinth, Eichhornia crassipes (Mart.) Solms (Pontederiaceae)
- Bownes, Angela, Hill, Martin P, Byrne, Marcus J
- Authors: Bownes, Angela , Hill, Martin P , Byrne, Marcus J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/406131 , vital:70241 , xlink:href="https://doi.org/10.1016/j.biocontrol.2013.07.023"
- Description: Environmental nutrient availability can drive and modify both plant responses to herbivory by phytophagous insects and insect feeding patterns which, in insect-weed systems, may ultimately determine whether biological control succeeds or fails. The impacts of insect biological control agents on the invasive aquatic weed, water hyacinth (Eichhornia crassipes) vary with nutrient levels in the environment. It was therefore considered important to evaluate nutrient-specific responses of E. crassipes to a grasshopper herbivore, Cornops aquaticum, prior to its release in South Africa. Both plant productivity and the response of E. crassipes to herbivory by C. aquaticum were nutrient dependent. Increases in plant biomass and leaf and ramet production were correlated with increases in nutrients in the water and plant biomass accumulation was reduced by herbivory at all three nutrient levels tested (high = 67%; medium = 100%; low = 400%). C. aquaticum nymphs fed E. crassipes leaves with the lowest nitrogen levels produced the highest biomass of frass during their development, indicating compensatory consumption. The results suggest that environmental nutrient availability will influence efficacy of C. aquaticum. They also provide further evidence that E. crassipes problems are exacerbated by an over-abundance of nutrients in aquatic environments, and that biological control would be a highly effective management tool if aquatic systems in South Africa were less polluted. Additionally, the results also show how an understanding of the fundamental responses of E. crassipes and its insect biocontrol agents to their environment can assist in determining specific management strategies or interventions according to prevailing site-specific conditions.
- Full Text:
- Date Issued: 2013
- Authors: Bownes, Angela , Hill, Martin P , Byrne, Marcus J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/406131 , vital:70241 , xlink:href="https://doi.org/10.1016/j.biocontrol.2013.07.023"
- Description: Environmental nutrient availability can drive and modify both plant responses to herbivory by phytophagous insects and insect feeding patterns which, in insect-weed systems, may ultimately determine whether biological control succeeds or fails. The impacts of insect biological control agents on the invasive aquatic weed, water hyacinth (Eichhornia crassipes) vary with nutrient levels in the environment. It was therefore considered important to evaluate nutrient-specific responses of E. crassipes to a grasshopper herbivore, Cornops aquaticum, prior to its release in South Africa. Both plant productivity and the response of E. crassipes to herbivory by C. aquaticum were nutrient dependent. Increases in plant biomass and leaf and ramet production were correlated with increases in nutrients in the water and plant biomass accumulation was reduced by herbivory at all three nutrient levels tested (high = 67%; medium = 100%; low = 400%). C. aquaticum nymphs fed E. crassipes leaves with the lowest nitrogen levels produced the highest biomass of frass during their development, indicating compensatory consumption. The results suggest that environmental nutrient availability will influence efficacy of C. aquaticum. They also provide further evidence that E. crassipes problems are exacerbated by an over-abundance of nutrients in aquatic environments, and that biological control would be a highly effective management tool if aquatic systems in South Africa were less polluted. Additionally, the results also show how an understanding of the fundamental responses of E. crassipes and its insect biocontrol agents to their environment can assist in determining specific management strategies or interventions according to prevailing site-specific conditions.
- Full Text:
- Date Issued: 2013
Overcrowding of false codling moth, Thaumatotibia leucotreta (Meyrick) leads to the isolation of five new Cryptophlebia leucotreta granulovirus (CrleGV-SA) isolates
- Opoku-Debrah, John K, Hill, Martin P, Knox, Caroline M, Moore, Sean D
- Authors: Opoku-Debrah, John K , Hill, Martin P , Knox, Caroline M , Moore, Sean D
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419360 , vital:71637 , xlink:href="https://doi.org/10.1016/j.jip.2012.12.008"
- Description: False codling moth, Thaumatotibia leucotreta (Meyrick) is a serious pest of economic importance to the South African fruit industry. As part of sustainable efforts to control this pest, biological control options that involve the application of baculovirus-based biopesticides such as Cryptogran and Cryptex (both formulated with a South African isolate of Cryptophlebia leucotreta granulovirus, CrleGV-SA) are popularly used by farmers. In order to safeguard the integrity of these biopesticides as well as protect against any future development of resistance in the host, we conducted a study to bioprospect for additional CrleGV isolates as alternatives to existing ones. Using overcrowding as an induction method for latent infection, we recovered five new CrleGV isolates (CrleGV-SA Ado, CrleGV-SA Mbl, CrleGV-SA Cit, CrleGV-SA MixC and CrleGV-SA Nels). Single restriction endonuclease (REN) analysis of viral genomic DNA extracted from purified occlusion bodies showed that isolates differed in their DNA profiles. Partial sequencing of granulin and egt genes from the different isolates and multiple alignments of nucleotide sequences revealed the presence of single nucleotide polymorphisms (SNPs), some of which resulted in amino acid substitutions in the protein sequence. Based on these findings as well as comparisons with other documented CrleGV isolates, we propose two phylogenetic groups for CrleGV-SA isolates recovered in this study.
- Full Text:
- Date Issued: 2013
- Authors: Opoku-Debrah, John K , Hill, Martin P , Knox, Caroline M , Moore, Sean D
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419360 , vital:71637 , xlink:href="https://doi.org/10.1016/j.jip.2012.12.008"
- Description: False codling moth, Thaumatotibia leucotreta (Meyrick) is a serious pest of economic importance to the South African fruit industry. As part of sustainable efforts to control this pest, biological control options that involve the application of baculovirus-based biopesticides such as Cryptogran and Cryptex (both formulated with a South African isolate of Cryptophlebia leucotreta granulovirus, CrleGV-SA) are popularly used by farmers. In order to safeguard the integrity of these biopesticides as well as protect against any future development of resistance in the host, we conducted a study to bioprospect for additional CrleGV isolates as alternatives to existing ones. Using overcrowding as an induction method for latent infection, we recovered five new CrleGV isolates (CrleGV-SA Ado, CrleGV-SA Mbl, CrleGV-SA Cit, CrleGV-SA MixC and CrleGV-SA Nels). Single restriction endonuclease (REN) analysis of viral genomic DNA extracted from purified occlusion bodies showed that isolates differed in their DNA profiles. Partial sequencing of granulin and egt genes from the different isolates and multiple alignments of nucleotide sequences revealed the presence of single nucleotide polymorphisms (SNPs), some of which resulted in amino acid substitutions in the protein sequence. Based on these findings as well as comparisons with other documented CrleGV isolates, we propose two phylogenetic groups for CrleGV-SA isolates recovered in this study.
- Full Text:
- Date Issued: 2013
Persistence and virulence of promising entomopathogenic fungal isolates for use in citrus orchards in South Africa
- Coombes, Candice A, Hill, Martin P, Moore, Sean D, Dames, Joanna F, Fullard, T
- Authors: Coombes, Candice A , Hill, Martin P , Moore, Sean D , Dames, Joanna F , Fullard, T
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416893 , vital:71394 , xlink:href="https://doi.org/10.1080/09583157.2013.819489"
- Description: Thaumatotibia leucotreta (Meyrick) (1912) (Lepidoptera: Tortricidae) is a key economic pest of citrus in South Africa. Although a variety of control options are available, none currently registered target the soil-dwelling life stages of the pest. Three fungal isolates, two Metarhizium anisopliae sensu lato Metschnikoff (Sorokin) isolates (G 11 3 L6 and FCM Ar 23 B3) and one Beauveria bassiana sensu lato Balsamo (Vuillemin) isolate (G Ar 17 B3) have been identified as showing the greatest potential against T. leucotreta soil-dwelling life stages. Since environmental persistence is an important factor in the success of entomopathogenic fungi against soil pests, the isolates, along with two commercial isolates (B. bassiana Eco-Bb® and M. anisopliae ICIPE 69), were subjected to a six-month field persistence trial. Every month after burial of the fungal isolates, inside net bags, in orchard soil, the number of colony forming units (CFUs) per gram of soil was measured and the viability of the conidia was assessed using bioassays. All isolates investigated were capable of persisting in the soil for the duration of the trial period and in addition, were capable of initiating infection in T. leucotreta late fifth instar larvae and subsequent pupae. However, with the exception of the commercial isolates which showed some correlation, no correlation was found between the number of CFUs recorded and percentage T. leucotreta mycosis. Persistence of entomopathogenic fungi in the field is affected by a series of factors, and although the effect of these factors was not measured, the data have provided preliminary evidence towards the persistence capability of these candidate biopesticides against T. leucotreta.
- Full Text:
- Date Issued: 2013
- Authors: Coombes, Candice A , Hill, Martin P , Moore, Sean D , Dames, Joanna F , Fullard, T
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/416893 , vital:71394 , xlink:href="https://doi.org/10.1080/09583157.2013.819489"
- Description: Thaumatotibia leucotreta (Meyrick) (1912) (Lepidoptera: Tortricidae) is a key economic pest of citrus in South Africa. Although a variety of control options are available, none currently registered target the soil-dwelling life stages of the pest. Three fungal isolates, two Metarhizium anisopliae sensu lato Metschnikoff (Sorokin) isolates (G 11 3 L6 and FCM Ar 23 B3) and one Beauveria bassiana sensu lato Balsamo (Vuillemin) isolate (G Ar 17 B3) have been identified as showing the greatest potential against T. leucotreta soil-dwelling life stages. Since environmental persistence is an important factor in the success of entomopathogenic fungi against soil pests, the isolates, along with two commercial isolates (B. bassiana Eco-Bb® and M. anisopliae ICIPE 69), were subjected to a six-month field persistence trial. Every month after burial of the fungal isolates, inside net bags, in orchard soil, the number of colony forming units (CFUs) per gram of soil was measured and the viability of the conidia was assessed using bioassays. All isolates investigated were capable of persisting in the soil for the duration of the trial period and in addition, were capable of initiating infection in T. leucotreta late fifth instar larvae and subsequent pupae. However, with the exception of the commercial isolates which showed some correlation, no correlation was found between the number of CFUs recorded and percentage T. leucotreta mycosis. Persistence of entomopathogenic fungi in the field is affected by a series of factors, and although the effect of these factors was not measured, the data have provided preliminary evidence towards the persistence capability of these candidate biopesticides against T. leucotreta.
- Full Text:
- Date Issued: 2013
Subterranean control of an arboreal pest: EPNs and EPFs for FCM
- Moore, Sean D, Coombes, Candice A, Manrakhan, Aruna, Kirkman, Wayne, Hill, Martin P, Ehlers, Ralf-Udo, Daneel, John-Henry, De Waal, Jeanne, Dames, Joanna F, Malan, Antoinette P
- Authors: Moore, Sean D , Coombes, Candice A , Manrakhan, Aruna , Kirkman, Wayne , Hill, Martin P , Ehlers, Ralf-Udo , Daneel, John-Henry , De Waal, Jeanne , Dames, Joanna F , Malan, Antoinette P
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/425450 , vital:72241 , xlink:href="https://www.cabdirect.org/cabdirect/abstract/20133257699"
- Description: Control measures against the false codling moth (FCM), Thaumatotibia leucotreta, have traditionally ignored the soil-borne pupal stage. Recent trials with entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPFs) have targeted this life-stage. Application of Heterorhabditis bacteriophora to a citrus orchard floor, reduced T. leucotreta infestation of fruit by up to 81%. Conservation of H. zealandica through non-usage of a nematicide also resulted in dramatically lower fruit infestation. Dose-response and exposure time-response bioassays identified the three most promising fungal isolates against pupating T. leucotreta. Orchard trials showed persistence of these fungi in orchard soil for at least six months.
- Full Text:
- Date Issued: 2013
- Authors: Moore, Sean D , Coombes, Candice A , Manrakhan, Aruna , Kirkman, Wayne , Hill, Martin P , Ehlers, Ralf-Udo , Daneel, John-Henry , De Waal, Jeanne , Dames, Joanna F , Malan, Antoinette P
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/425450 , vital:72241 , xlink:href="https://www.cabdirect.org/cabdirect/abstract/20133257699"
- Description: Control measures against the false codling moth (FCM), Thaumatotibia leucotreta, have traditionally ignored the soil-borne pupal stage. Recent trials with entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPFs) have targeted this life-stage. Application of Heterorhabditis bacteriophora to a citrus orchard floor, reduced T. leucotreta infestation of fruit by up to 81%. Conservation of H. zealandica through non-usage of a nematicide also resulted in dramatically lower fruit infestation. Dose-response and exposure time-response bioassays identified the three most promising fungal isolates against pupating T. leucotreta. Orchard trials showed persistence of these fungi in orchard soil for at least six months.
- Full Text:
- Date Issued: 2013
The effect of herbivory by the mite Orthogalumna terebrantis on the growth and photosynthetic performance of water hyacinth (Eichhornia crassipes)
- Marlin, Danica, Hill, Martin P, Ripley, Bradford S, Strauss, Abram J, Byrne, Marcus J
- Authors: Marlin, Danica , Hill, Martin P , Ripley, Bradford S , Strauss, Abram J , Byrne, Marcus J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419411 , vital:71642 , xlink:href="https://doi.org/10.1016/j.aquabot.2012.09.005"
- Description: Eutrophication of fresh water systems is one of the most important factors contributing to the invasion of fresh water bodies by water hyacinth, Eichhornia crassipes. The South American mite, Orthogalumna terebrantis, established on the weed in South Africa in the late 1980s, but the impact of mite herbivory on the weed has never been quantified. Water hyacinth was grown under low, medium and high nitrogen and phosphorus nutrient conditions and the effect of mite herbivory on the weed's growth was examined. Additionally, the impact of different mite herbivory intensities on the weed's photosynthetic performance was examined because herbivory may have more subtle effects on the plant than can be seen from changes in plant growth parameters. Water nutrient content had a great impact on plant growth, but growth was unaffected by mite herbivory in all levels of nutrients tested. Photosynthetic performance of water hyacinth leaves exposed to varying levels of mite herbivory was assessed by measuring net photosynthetic rate (A), leaf conductance (gl), transpiration rate (E) and intercellular CO2 concentration (Ci), and by measuring specific fluorescence parameters including maximal fluorescence (Fm), efficiency of photosystem II (Fv/Fm) and certain JIP-test parameters. Photosynthesis decreased as mite herbivory increased, but there was a positive correlation between gl, E and Ci, and the amount of leaf tissue damaged through mite feeding. The efficiency of photosystem II (PSII) decreased as mite herbivory increased, as seen in the altered fluorescence emission of mite-damaged plants, but this was not the consequence of decreased chlorophyll content. Feeding by O. terebrantis thus decreased water hyacinth photosynthetic rate and the light reaction performance, even at relatively low mite densities. These results show that the impact of a biological control agent on its host plant may not be obvious at a plant growth level, but may nonetheless affect the plant at a physiological level.
- Full Text:
- Date Issued: 2013
- Authors: Marlin, Danica , Hill, Martin P , Ripley, Bradford S , Strauss, Abram J , Byrne, Marcus J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/419411 , vital:71642 , xlink:href="https://doi.org/10.1016/j.aquabot.2012.09.005"
- Description: Eutrophication of fresh water systems is one of the most important factors contributing to the invasion of fresh water bodies by water hyacinth, Eichhornia crassipes. The South American mite, Orthogalumna terebrantis, established on the weed in South Africa in the late 1980s, but the impact of mite herbivory on the weed has never been quantified. Water hyacinth was grown under low, medium and high nitrogen and phosphorus nutrient conditions and the effect of mite herbivory on the weed's growth was examined. Additionally, the impact of different mite herbivory intensities on the weed's photosynthetic performance was examined because herbivory may have more subtle effects on the plant than can be seen from changes in plant growth parameters. Water nutrient content had a great impact on plant growth, but growth was unaffected by mite herbivory in all levels of nutrients tested. Photosynthetic performance of water hyacinth leaves exposed to varying levels of mite herbivory was assessed by measuring net photosynthetic rate (A), leaf conductance (gl), transpiration rate (E) and intercellular CO2 concentration (Ci), and by measuring specific fluorescence parameters including maximal fluorescence (Fm), efficiency of photosystem II (Fv/Fm) and certain JIP-test parameters. Photosynthesis decreased as mite herbivory increased, but there was a positive correlation between gl, E and Ci, and the amount of leaf tissue damaged through mite feeding. The efficiency of photosystem II (PSII) decreased as mite herbivory increased, as seen in the altered fluorescence emission of mite-damaged plants, but this was not the consequence of decreased chlorophyll content. Feeding by O. terebrantis thus decreased water hyacinth photosynthetic rate and the light reaction performance, even at relatively low mite densities. These results show that the impact of a biological control agent on its host plant may not be obvious at a plant growth level, but may nonetheless affect the plant at a physiological level.
- Full Text:
- Date Issued: 2013
Using a unified invasion framework to characterize Africa’s first loricariid catfish invasion
- Jones, Roy W, Weyl, Olaf L F, Hill, Martin P, Swartz, Ernst R
- Authors: Jones, Roy W , Weyl, Olaf L F , Hill, Martin P , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/418081 , vital:71507 , xlink:href="https://doi.org/10.1007/s10530-013-0438-7"
- Description: This paper presents evidence of establishment of a loricariid population in the Nseleni River in South Africa and uses a unified framework to determine its invasion stage. Specimens were identified morphologically as Pterygioplichthys disjunctivus (Weber 1991), but genetic barcoding results indicated close association with specimens that may have a hybrid history. The species was introduced into South Africa via the pet trade and the first record of introduction into the wild was in 2004. Samples collected in 2011 and 2012 demonstrated that there were multiple length cohorts in the population including juveniles (12–130 mm total length TL) and large (>300 mm TL) adult fish. Gonadal assessment of adults demonstrated the presence of reproduction capable specimens. The concurrent occurrence of mature adults and juvenile fish demonstrated establishment. Locality records indicate that P. disjunctivus has already spread between two rivers through an inter basin water transfer. Using a unified framework for invasions this invasion was categorized as a self-sustaining population in the wild with individuals surviving and reproducing a significant distance from their original point of introduction. Containment is suggested as potential management strategy.
- Full Text:
- Date Issued: 2013
- Authors: Jones, Roy W , Weyl, Olaf L F , Hill, Martin P , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/418081 , vital:71507 , xlink:href="https://doi.org/10.1007/s10530-013-0438-7"
- Description: This paper presents evidence of establishment of a loricariid population in the Nseleni River in South Africa and uses a unified framework to determine its invasion stage. Specimens were identified morphologically as Pterygioplichthys disjunctivus (Weber 1991), but genetic barcoding results indicated close association with specimens that may have a hybrid history. The species was introduced into South Africa via the pet trade and the first record of introduction into the wild was in 2004. Samples collected in 2011 and 2012 demonstrated that there were multiple length cohorts in the population including juveniles (12–130 mm total length TL) and large (>300 mm TL) adult fish. Gonadal assessment of adults demonstrated the presence of reproduction capable specimens. The concurrent occurrence of mature adults and juvenile fish demonstrated establishment. Locality records indicate that P. disjunctivus has already spread between two rivers through an inter basin water transfer. Using a unified framework for invasions this invasion was categorized as a self-sustaining population in the wild with individuals surviving and reproducing a significant distance from their original point of introduction. Containment is suggested as potential management strategy.
- Full Text:
- Date Issued: 2013
Weevil borne microbes contribute as much to the reduction of photosynthesis in water hyacinth as does herbivory
- Venter, Nic, Hill, Martin P, Hutchinson, Sarah-Leigh, Ripley, Bradford S
- Authors: Venter, Nic , Hill, Martin P , Hutchinson, Sarah-Leigh , Ripley, Bradford S
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423573 , vital:72073 , xlink:href="https://doi.org/10.1016/j.biocontrol.2012.10.011"
- Description: Arthropods released for weed biocontrol can have effects other than simply removing biomass and frequently decrease photosynthetic rate more than can be attributed to the mere loss of photosynthetic surface area. Some of this effect may result because biological control agents facilitate the transfer and ingress of deleterious microbes into plant tissues on which they feed. We evaluated this facilitation effect using water hyacinth (Eichhornia crassipes) and a weevil (Neochetina eichhorniae) and compared the reductions in photosynthetic rates between leaves subject to herbivory by adult weevils sterilized with 3.5% chlorine bleach, to those that were unsterilized. The results showed that weevils carried both fungi and bacteria, transferred these to leaves on which they fed, and that microbes and biomass removal contributed almost equally to the 37% decrease in photosynthetic productivity. Hence, maximising the effectiveness of using arthropods that damage leaf surfaces for biocontrol requires the presence of microorganisms that are deleterious to plants.
- Full Text:
- Date Issued: 2013
- Authors: Venter, Nic , Hill, Martin P , Hutchinson, Sarah-Leigh , Ripley, Bradford S
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423573 , vital:72073 , xlink:href="https://doi.org/10.1016/j.biocontrol.2012.10.011"
- Description: Arthropods released for weed biocontrol can have effects other than simply removing biomass and frequently decrease photosynthetic rate more than can be attributed to the mere loss of photosynthetic surface area. Some of this effect may result because biological control agents facilitate the transfer and ingress of deleterious microbes into plant tissues on which they feed. We evaluated this facilitation effect using water hyacinth (Eichhornia crassipes) and a weevil (Neochetina eichhorniae) and compared the reductions in photosynthetic rates between leaves subject to herbivory by adult weevils sterilized with 3.5% chlorine bleach, to those that were unsterilized. The results showed that weevils carried both fungi and bacteria, transferred these to leaves on which they fed, and that microbes and biomass removal contributed almost equally to the 37% decrease in photosynthetic productivity. Hence, maximising the effectiveness of using arthropods that damage leaf surfaces for biocontrol requires the presence of microorganisms that are deleterious to plants.
- Full Text:
- Date Issued: 2013
A quantitative post-release evaluation of biological control of water lettuce, Pistia stratiotes L. (Araceae) by the weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae) at Cape Recife Nature Reserve, Eastern Cape Province, South Africa
- Moore, Gareth R, Hill, Martin P
- Authors: Moore, Gareth R , Hill, Martin P
- Date: 2012
- Language: English
- Type: text , Article
- Identifier: vital:6839 , http://hdl.handle.net/10962/d1010987 , http://dx.doi.org/10.4001/003.020.0217 , https://orcid.org/0000-0003-0579-5298
- Description: [from the introduction] Water lettuce, Pistia stratiotes L. (Araceae) is recognized as being among the world’s worst aquatic weeds. In its adventive range, the plant forms extensive mats capable of blocking navigation channels, impeding water flow in irrigation and flood control canals, and disrupting hydropower generation (Holm et al. 1977). Dense mats of the weed prevent light penetration into the water column which negatively affects submerged aquatic plant communities, causing a lowering of the oxygen concentration and thereby reducing benthic invertebrate and fish populations (Neuenschwander et al. 2009).
- Full Text:
- Date Issued: 2012
- Authors: Moore, Gareth R , Hill, Martin P
- Date: 2012
- Language: English
- Type: text , Article
- Identifier: vital:6839 , http://hdl.handle.net/10962/d1010987 , http://dx.doi.org/10.4001/003.020.0217 , https://orcid.org/0000-0003-0579-5298
- Description: [from the introduction] Water lettuce, Pistia stratiotes L. (Araceae) is recognized as being among the world’s worst aquatic weeds. In its adventive range, the plant forms extensive mats capable of blocking navigation channels, impeding water flow in irrigation and flood control canals, and disrupting hydropower generation (Holm et al. 1977). Dense mats of the weed prevent light penetration into the water column which negatively affects submerged aquatic plant communities, causing a lowering of the oxygen concentration and thereby reducing benthic invertebrate and fish populations (Neuenschwander et al. 2009).
- Full Text:
- Date Issued: 2012
Baseline isotope data for Spirodela sp.: nutrient differentiation in aquatic systems
- Hill, Jaclyn M, Kaehler, Sven, Hill, Martin P
- Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444502 , vital:74246 , https://doi.org/10.1016/j.watres.2012.03.063
- Description: The excessive addition of nitrogen to watersheds is recognized as one of the main causes of the global deterioration of aquatic ecosystems and an increasing number of studies have shown that δ15N signatures of macrophytes may reflect the N-loading of the system under investigation. This study investigated isotopic equilibration rates and concentration level effects of KNO3 and cow manure nutrient solutions on the δ15N and δ13C signatures, C/N ratios, % N and % C of Spirodela sp. over time, to determine the feasibility of their use in monitoring anthropogenic N-loading in freshwater systems. Spirodela δ15N signatures clearly distinguished between nutrient types within 2 days of introduction, with plants grown in KNO3 showing extremely depleted δ15N values (−15.00 to −12.00‰) compared to those growing in cow manure (14.00–18.00‰). Isotopic equilibration rates could not be determined with certainty, but plant isotopic differentiation between nutrient regimes became apparent after 2 days and started to equilibrate by day 4. Concentration level effects were also apparent, with Spirodela tissue displaying more depleted and enriched δ15N values in higher concentrations of KNO3 and cow manure respectively.
- Full Text:
- Date Issued: 2012
- Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444502 , vital:74246 , https://doi.org/10.1016/j.watres.2012.03.063
- Description: The excessive addition of nitrogen to watersheds is recognized as one of the main causes of the global deterioration of aquatic ecosystems and an increasing number of studies have shown that δ15N signatures of macrophytes may reflect the N-loading of the system under investigation. This study investigated isotopic equilibration rates and concentration level effects of KNO3 and cow manure nutrient solutions on the δ15N and δ13C signatures, C/N ratios, % N and % C of Spirodela sp. over time, to determine the feasibility of their use in monitoring anthropogenic N-loading in freshwater systems. Spirodela δ15N signatures clearly distinguished between nutrient types within 2 days of introduction, with plants grown in KNO3 showing extremely depleted δ15N values (−15.00 to −12.00‰) compared to those growing in cow manure (14.00–18.00‰). Isotopic equilibration rates could not be determined with certainty, but plant isotopic differentiation between nutrient regimes became apparent after 2 days and started to equilibrate by day 4. Concentration level effects were also apparent, with Spirodela tissue displaying more depleted and enriched δ15N values in higher concentrations of KNO3 and cow manure respectively.
- Full Text:
- Date Issued: 2012
Toxic effect of herbicides used for water hyacinth control on two insects released for its biological control in South Africa
- Authors: Hill, Martin P
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69960 , vital:29601 , https://doi.org/10.1080/09583157.2012.725825
- Description: The integrated control of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) has become necessary in South Africa, as biological control alone is perceived to be too slow in controlling the weed. In total, seven insect biological control agents have been released on water hyacinth in South Africa. At the same time, herbicides are applied by the water authorities in areas where the weed continues to be troublesome. This study investigated the assumption that the two control methods are compatible by testing the direct toxicity of a range of herbicide formulations and surfactants on two of the biological control agents released against water hyacinth, the weevil, Neochetina eichhorniae Warner (Coleoptera: Curculionidae) and the water hyacinth mirid,Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae). A number of the formulations used resulted in significant mortality of the mirid and the weevil. Products containing 2,4-D amine and diquat as active ingredients caused higher mortality of both agents (up to 80% for the mirid) than formulations containing glyphosate. Furthermore, when surfactants were added to enhance herbicide efficiency, it resulted in increased toxicity to the insects. We recommend that glyphosate formulations should be used in integrated control programmes, and that surfactants be avoided in order to reduce the toxic nature of spray formulations to the insect biological control agents released against water hyacinth.
- Full Text:
- Date Issued: 2012
- Authors: Hill, Martin P
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69960 , vital:29601 , https://doi.org/10.1080/09583157.2012.725825
- Description: The integrated control of water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae) has become necessary in South Africa, as biological control alone is perceived to be too slow in controlling the weed. In total, seven insect biological control agents have been released on water hyacinth in South Africa. At the same time, herbicides are applied by the water authorities in areas where the weed continues to be troublesome. This study investigated the assumption that the two control methods are compatible by testing the direct toxicity of a range of herbicide formulations and surfactants on two of the biological control agents released against water hyacinth, the weevil, Neochetina eichhorniae Warner (Coleoptera: Curculionidae) and the water hyacinth mirid,Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae). A number of the formulations used resulted in significant mortality of the mirid and the weevil. Products containing 2,4-D amine and diquat as active ingredients caused higher mortality of both agents (up to 80% for the mirid) than formulations containing glyphosate. Furthermore, when surfactants were added to enhance herbicide efficiency, it resulted in increased toxicity to the insects. We recommend that glyphosate formulations should be used in integrated control programmes, and that surfactants be avoided in order to reduce the toxic nature of spray formulations to the insect biological control agents released against water hyacinth.
- Full Text:
- Date Issued: 2012
Water hyacinth, Eichhornia crassipes (Pontederiaceae), reduces benthic macroinvertebrate diversity in a protected subtropical lake in South Africa
- Coetzee, Julie A, Jones, Roy W, Hill, Martin P
- Authors: Coetzee, Julie A , Jones, Roy W , Hill, Martin P
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/479023 , vital:78252 , https://doi.org/10.1007/s10531-014-0667-9
- Description: The socio-economic impacts of the free-floating aquatic plant water hyacinth, Eichhornia crassipes (Pontederiaceae), on aquatic systems are well documented, yet the impacts on aquatic biodiversity, particularly invertebrate biodiversity, are less well understood. This study aimed to determine whether the presence of water hyacinth altered the diversity and assemblage structure of benthic macroinvertebrates in a conservation area. The benthic macroinvertebrate assemblage was sampled over 1 year at five sites under water hyacinth mats and at five sites without water hyacinth at Lake Nsezi—Nseleni River in the vicinity of Richards Bay, KwaZulu-Natal, South Africa. Artificial substrates were placed beneath water hyacinth mats or in the open water to allow for colonization by freshwater macroinvertebrates, and left for a period of 6 weeks, repeated on seven occasions. Twenty nine families comprising 18,797 individuals were collected, 817 (13 families) individuals were from under water hyacinth mat sites compared to 17,980 (27 families) individuals from open water sites.
- Full Text:
- Date Issued: 2012
- Authors: Coetzee, Julie A , Jones, Roy W , Hill, Martin P
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/479023 , vital:78252 , https://doi.org/10.1007/s10531-014-0667-9
- Description: The socio-economic impacts of the free-floating aquatic plant water hyacinth, Eichhornia crassipes (Pontederiaceae), on aquatic systems are well documented, yet the impacts on aquatic biodiversity, particularly invertebrate biodiversity, are less well understood. This study aimed to determine whether the presence of water hyacinth altered the diversity and assemblage structure of benthic macroinvertebrates in a conservation area. The benthic macroinvertebrate assemblage was sampled over 1 year at five sites under water hyacinth mats and at five sites without water hyacinth at Lake Nsezi—Nseleni River in the vicinity of Richards Bay, KwaZulu-Natal, South Africa. Artificial substrates were placed beneath water hyacinth mats or in the open water to allow for colonization by freshwater macroinvertebrates, and left for a period of 6 weeks, repeated on seven occasions. Twenty nine families comprising 18,797 individuals were collected, 817 (13 families) individuals were from under water hyacinth mat sites compared to 17,980 (27 families) individuals from open water sites.
- Full Text:
- Date Issued: 2012
A context for the 2011 compilation of reviews on the biological control of invasive alien plants in South Africa
- Moran, V Clifford, Hoffmann, John C, Hill, Martin P
- Authors: Moran, V Clifford , Hoffmann, John C , Hill, Martin P
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451270 , vital:75035 , https://hdl.handle.net/10520/EJC32923
- Description: 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.
- Full Text:
- Date Issued: 2011
- Authors: Moran, V Clifford , Hoffmann, John C , Hill, Martin P
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451270 , vital:75035 , https://hdl.handle.net/10520/EJC32923
- Description: 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.
- Full Text:
- Date Issued: 2011
A review of the biological control programmes on Eichhornia crassipes (C. mart.) solms (Pontederiaceae), Salvinia molesta DS Mitch.(Salviniaceae), Pistia stratiotes L.(Araceae), Myriophyllum aquaticum (vell.) verdc.(Haloragaceae) and Azolla filiculoides Lam.(Azollaceae) in South Africa
- Coetzee, Julie A, Hill, Martin P, Byrne, Marcus J
- Authors: Coetzee, Julie A , Hill, Martin P , Byrne, Marcus J
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451285 , vital:75036 , https://hdl.handle.net/10520/EJC32900
- Description: 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.
- Full Text:
- Date Issued: 2011
- Authors: Coetzee, Julie A , Hill, Martin P , Byrne, Marcus J
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451285 , vital:75036 , https://hdl.handle.net/10520/EJC32900
- Description: 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.
- Full Text:
- Date Issued: 2011
A stable isotope approach for the early detection and identification of N loading in aquatic ecosystems
- Hill, Jaclyn M, Kaehler, Sven, Hill, Martin P, Coetzee, Julie A
- Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P , Coetzee, Julie A
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444491 , vital:74245 , https://www.wrc.org.za/wp-content/uploads/mdocs/KV 280.pdf
- Description: Global increases in urbanization and anthropogenic activity within wa-tersheds and catchment areas have resulted in excessive nitrogen loads in aquatic ecosystems. South Africa is deeply dependent on nat-ural resources for its economic health and as a consequence is particu-larly vulnerable to the degradation of its natural capital. Increased nitro-gen loading can result in widespread aquatic ecosystem degradation including: harmful algal blooms, increased turbidity, hypoxia, loss of aquatic vegetation and habitat and fish kills, it is also one of the mecha-nisms driving aquatic weed invasions. Understanding the fate and pro-cessing of anthropogenic nutrients in natural systems is therefore criti-cal for both preserving the well-being and biotic heritage for future gen-erations as well as providing a tremendous opportunity to improve the management driven by science. The objectives of this study were to evaluate the feasibility of mapping anthropogenic pollution through sta-ble isotopes signatures of aquatic plants, to investigate the potential for identifying different pollution sources, concentrations and distributions in a freshwater environment and to determine the utility of these tech-niques in indentifying early eutrophication.
- Full Text:
- Date Issued: 2011
- Authors: Hill, Jaclyn M , Kaehler, Sven , Hill, Martin P , Coetzee, Julie A
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444491 , vital:74245 , https://www.wrc.org.za/wp-content/uploads/mdocs/KV 280.pdf
- Description: Global increases in urbanization and anthropogenic activity within wa-tersheds and catchment areas have resulted in excessive nitrogen loads in aquatic ecosystems. South Africa is deeply dependent on nat-ural resources for its economic health and as a consequence is particu-larly vulnerable to the degradation of its natural capital. Increased nitro-gen loading can result in widespread aquatic ecosystem degradation including: harmful algal blooms, increased turbidity, hypoxia, loss of aquatic vegetation and habitat and fish kills, it is also one of the mecha-nisms driving aquatic weed invasions. Understanding the fate and pro-cessing of anthropogenic nutrients in natural systems is therefore criti-cal for both preserving the well-being and biotic heritage for future gen-erations as well as providing a tremendous opportunity to improve the management driven by science. The objectives of this study were to evaluate the feasibility of mapping anthropogenic pollution through sta-ble isotopes signatures of aquatic plants, to investigate the potential for identifying different pollution sources, concentrations and distributions in a freshwater environment and to determine the utility of these tech-niques in indentifying early eutrophication.
- Full Text:
- Date Issued: 2011
Regulation and risk assessment for importations and releases of biological control agents against invasive alien plants in South Africa
- Klein, Hildegard, Hill, Martin P, Zachariades, Costas, Zimmermann, Helmuth G
- Authors: Klein, Hildegard , Hill, Martin P , Zachariades, Costas , Zimmermann, Helmuth G
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451481 , vital:75052 , https://hdl.handle.net/10520/EJC32898
- Description: 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.
- Full Text:
- Date Issued: 2011
- Authors: Klein, Hildegard , Hill, Martin P , Zachariades, Costas , Zimmermann, Helmuth G
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451481 , vital:75052 , https://hdl.handle.net/10520/EJC32898
- Description: 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.
- Full Text:
- Date Issued: 2011
The role of eutrophication in the biological control of water hyacinth, Eichhornia crassipes, in South Africa
- Coetzee, Julie A, Hill, Martin P
- Authors: Coetzee, Julie A , Hill, Martin P
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69263 , vital:29474 , https://doi.org/10.1007/s10526-011-9426-y
- Description: South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of an unnecessarily high 1 mg l-1 phosphorus (P) standard for all water treatment works in the 1970 s. The floating aquatic macrophyte, water hyacinth (Eichhornia crassipes (Mart.) Solms (Pontederiaceae), has taken advantage of these nutrient rich systems, becoming highly invasive and damaging. Despite the implementation of a biological control programme in South Africa, water hyacinth remains the worst aquatic weed. A meta-analysis of published and unpublished laboratory studies that investigated the combined effect of P and nitrogen (N) water nutrient concentration and control agent herbivory showed that water nutrient status was more important than herbivory in water hyacinth growth. Analysis of long-term field data collected monthly from 14 sites around South Africa between 2004 and 2005 supported these findings. Therefore, the first step in any water hyacinth control programme should be to reduce the nutrient status of the water body.
- Full Text:
- Date Issued: 2011
- Authors: Coetzee, Julie A , Hill, Martin P
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69263 , vital:29474 , https://doi.org/10.1007/s10526-011-9426-y
- Description: South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of an unnecessarily high 1 mg l-1 phosphorus (P) standard for all water treatment works in the 1970 s. The floating aquatic macrophyte, water hyacinth (Eichhornia crassipes (Mart.) Solms (Pontederiaceae), has taken advantage of these nutrient rich systems, becoming highly invasive and damaging. Despite the implementation of a biological control programme in South Africa, water hyacinth remains the worst aquatic weed. A meta-analysis of published and unpublished laboratory studies that investigated the combined effect of P and nitrogen (N) water nutrient concentration and control agent herbivory showed that water nutrient status was more important than herbivory in water hyacinth growth. Analysis of long-term field data collected monthly from 14 sites around South Africa between 2004 and 2005 supported these findings. Therefore, the first step in any water hyacinth control programme should be to reduce the nutrient status of the water body.
- Full Text:
- Date Issued: 2011
Natural enemies from South Africa for biological control of Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae) in Europe
- Baars, Jan-Robert, Coetzee, Julie A, Martin, Grant D, Hill, Martin P, Caffrey, J M
- Authors: Baars, Jan-Robert , Coetzee, Julie A , Martin, Grant D , Hill, Martin P , Caffrey, J M
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76914 , vital:30637 , https://doi.org/10.1007/s10750-010-0427-0
- Description: The non-native invasive plant, Lagarosiphon major (Hydrocharitaceae) is a submersed aquatic macrophyte that poses a significant threat to water bodies in Europe. Dense infestations prove difficult to manage using traditional methods. In order to initiate a biocontrol programme, a survey for natural enemies of Lagarosiphon was conducted in South Africa. Several phytophagous species were recorded for the first time, with at least three showing notable promise as candidate agents. Amongst these, a leaf-mining fly, Hydrellia sp. (Ephydridae) that occurred over a wide distribution causes significant leaf damage despite high levels of parasitism by braconid wasps. Another yet unidentified fly was recorded mining the stem of L. major. Two leaf-feeding and shoot boring weevils, cf. Bagous sp. (Curculionidae) were recorded damaging the shoot tips and stunting the growth of the stem. Several leaf-feeding lepidopteran species (Nymphulinae) were frequently recorded, but are expected to feed on a wide range of plant species and are not considered for importation before other candidates are assessed. The discovery of several natural enemies in the country of origin improves the biological control prospects of L. major in Europe.
- Full Text:
- Date Issued: 2010
- Authors: Baars, Jan-Robert , Coetzee, Julie A , Martin, Grant D , Hill, Martin P , Caffrey, J M
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76914 , vital:30637 , https://doi.org/10.1007/s10750-010-0427-0
- Description: The non-native invasive plant, Lagarosiphon major (Hydrocharitaceae) is a submersed aquatic macrophyte that poses a significant threat to water bodies in Europe. Dense infestations prove difficult to manage using traditional methods. In order to initiate a biocontrol programme, a survey for natural enemies of Lagarosiphon was conducted in South Africa. Several phytophagous species were recorded for the first time, with at least three showing notable promise as candidate agents. Amongst these, a leaf-mining fly, Hydrellia sp. (Ephydridae) that occurred over a wide distribution causes significant leaf damage despite high levels of parasitism by braconid wasps. Another yet unidentified fly was recorded mining the stem of L. major. Two leaf-feeding and shoot boring weevils, cf. Bagous sp. (Curculionidae) were recorded damaging the shoot tips and stunting the growth of the stem. Several leaf-feeding lepidopteran species (Nymphulinae) were frequently recorded, but are expected to feed on a wide range of plant species and are not considered for importation before other candidates are assessed. The discovery of several natural enemies in the country of origin improves the biological control prospects of L. major in Europe.
- Full Text:
- Date Issued: 2010
Quantitative post-release evaluation of biological control of floating fern, Salvinia molesta DS Mitchell (Salviniaceae), with Cyrtobagous salviniae Calder and Sands (Coleoptera Curculionidae) on the Senegal River and Senegal River Delta
- Diop Ousseynou, Hill, Martin P
- Authors: Diop Ousseynou , Hill, Martin P
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451467 , vital:75051 , https://hdl.handle.net/10520/EJC32802
- Description: The floating aquatic fern, Salvinia molesta D.S Mitchell (Salviniaceae) was first recorded in Senegal in 1999 and by 2000 it covered an estimated area of 18 000 ha on the Senegal River Left Bank and tributaries (Senegal) and 7840 ha on the Senegal River Right Bank (Mauritania). The weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) was considered the best option for control and some 48 953 weevils were released at 270 sites during 2002. Within one year, weevils had established and were recovered up to 50km from the release sites. At most of the release sites, the S. molesta infestation was reduced from 100 % to less than 5 % within 24 months of release. These results are discussed in the context of the weed's negative impact on aquatic systems.
- Full Text:
- Date Issued: 2009
- Authors: Diop Ousseynou , Hill, Martin P
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451467 , vital:75051 , https://hdl.handle.net/10520/EJC32802
- Description: The floating aquatic fern, Salvinia molesta D.S Mitchell (Salviniaceae) was first recorded in Senegal in 1999 and by 2000 it covered an estimated area of 18 000 ha on the Senegal River Left Bank and tributaries (Senegal) and 7840 ha on the Senegal River Right Bank (Mauritania). The weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) was considered the best option for control and some 48 953 weevils were released at 270 sites during 2002. Within one year, weevils had established and were recovered up to 50km from the release sites. At most of the release sites, the S. molesta infestation was reduced from 100 % to less than 5 % within 24 months of release. These results are discussed in the context of the weed's negative impact on aquatic systems.
- Full Text:
- Date Issued: 2009
Baited traps may be an alternative to conventional pesticides in the integrated crop management of chicory (Compositae) in South Africa
- Midgley, John M, Hill, Martin P, Villet, Martin H
- Authors: Midgley, John M , Hill, Martin P , Villet, Martin H
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6858 , http://hdl.handle.net/10962/d1011141 , http://dx.doi.org/10.1603/0022-0493(2008)101[99:BTMBAA]2.0.CO;2 , https://orcid.org/0000-0003-0579-5298
- Description: Chicory, Chicorium intybus L. (Compositae), is a major field crop in the Eastern Cape Province of South Africa. Several pests feed on the leaves of the plant, resulting in reduced yield. The most important of these are the noctuid moths Helicoverpa armigera (Hübner), Chrysodeixis acuta (Walker), and Trichoplusia orichalcea (F.). The use of attract-and-kill traps offers an alternative to broad-based insecticides in the control of these species. Three fields were treated with normal insecticides and three fields with yellow-baited traps. Eight additional traps were placed in each field, with half of the traps containing the insecticide 2,2-dichlorovinyl dimethyl phosphate (dichlorvos) and half without dichlorvos; and half yellow and half green. Total moth numbers and nonphytophage diversity were measured from these eight traps. Although no differences in H. armigera or T. orichalcea catches were observed between insecticide- and trap-treated fields, numbers of C. acuta and the total number of moths were significantly higher in insecticide-treated fields. Yellow traps containing dichlorvos contained more moths than yellow traps without dichlorvos, or green traps with dichlorvos, or green traps without dichlorvos; but they also contained more nonphytophagous insects. Yellow traps also enhanced the catches of thrips on card traps associated with them. These results offer an opportunity for the South African chicory industry to reduce pesticide applications and thus mitigate environmental impacts.
- Full Text:
- Date Issued: 2008
- Authors: Midgley, John M , Hill, Martin P , Villet, Martin H
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6858 , http://hdl.handle.net/10962/d1011141 , http://dx.doi.org/10.1603/0022-0493(2008)101[99:BTMBAA]2.0.CO;2 , https://orcid.org/0000-0003-0579-5298
- Description: Chicory, Chicorium intybus L. (Compositae), is a major field crop in the Eastern Cape Province of South Africa. Several pests feed on the leaves of the plant, resulting in reduced yield. The most important of these are the noctuid moths Helicoverpa armigera (Hübner), Chrysodeixis acuta (Walker), and Trichoplusia orichalcea (F.). The use of attract-and-kill traps offers an alternative to broad-based insecticides in the control of these species. Three fields were treated with normal insecticides and three fields with yellow-baited traps. Eight additional traps were placed in each field, with half of the traps containing the insecticide 2,2-dichlorovinyl dimethyl phosphate (dichlorvos) and half without dichlorvos; and half yellow and half green. Total moth numbers and nonphytophage diversity were measured from these eight traps. Although no differences in H. armigera or T. orichalcea catches were observed between insecticide- and trap-treated fields, numbers of C. acuta and the total number of moths were significantly higher in insecticide-treated fields. Yellow traps containing dichlorvos contained more moths than yellow traps without dichlorvos, or green traps with dichlorvos, or green traps without dichlorvos; but they also contained more nonphytophagous insects. Yellow traps also enhanced the catches of thrips on card traps associated with them. These results offer an opportunity for the South African chicory industry to reduce pesticide applications and thus mitigate environmental impacts.
- Full Text:
- Date Issued: 2008
Characterization of a succession of small insect viruses in a wild South African population of Nudaurelia cytherea capensis (Lepidoptera: Saturniidae)
- Walter, Cheryl T, Tomasicchio, Michelle, Hodgson, V, Hendry, Donald A, Hill, Martin P, Dorrington, Rosemary A
- Authors: Walter, Cheryl T , Tomasicchio, Michelle , Hodgson, V , Hendry, Donald A , Hill, Martin P , Dorrington, Rosemary A
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6474 , http://hdl.handle.net/10962/d1006161 , http://www.scielo.org.za/scielo.php?pid=S0038-23532008000200015&script=sci_arttext
- Description: The Tetraviridae are a family of small insect RNA viruses first discovered in South Africa some 40 years ago. They consist of one or two single-stranded (+) RNAs encapsidated in an icosahedral capsid of approximately 40 nm in diameter, with T = 4 symmetry. The type members of the two genera within this family, Nudaurelia β virus (NβV) and Nudaurelia ω virus (NωV), infect Nudaurelia cytherea capensis (pine emperor moth) larvae. The absence of N. capensis laboratory colonies and tissue culture cell lines susceptible to virus infection have limited research on the biology of NβV and NωV because the availability of infectious virus is dependent upon sporadic outbreaks in the wild N. capensis populations. In September 2002, dead and dying N. capensis larvae exhibiting symptoms similar to those reported previously in other tetravirus infections were observed in a wild population in a pine forest in the Western Cape province of South Africa. We report here the isolation of three small insect viruses from this population over a period of three years. Transmission electron microscopy and serological characterization indicate that all three are tetra-like virus isolates. One isolate was shown by cDNA sequence analysis to be NβV, which was thought to have been extinct since 1985. The two other isolates are likely new tetraviruses, designated Nudaurelia ψ virus (NψV) and Nudaurelia ζ virus (NζV), which are morphologically and serologically related to NωV and NβV, respectively.
- Full Text:
- Date Issued: 2008
- Authors: Walter, Cheryl T , Tomasicchio, Michelle , Hodgson, V , Hendry, Donald A , Hill, Martin P , Dorrington, Rosemary A
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6474 , http://hdl.handle.net/10962/d1006161 , http://www.scielo.org.za/scielo.php?pid=S0038-23532008000200015&script=sci_arttext
- Description: The Tetraviridae are a family of small insect RNA viruses first discovered in South Africa some 40 years ago. They consist of one or two single-stranded (+) RNAs encapsidated in an icosahedral capsid of approximately 40 nm in diameter, with T = 4 symmetry. The type members of the two genera within this family, Nudaurelia β virus (NβV) and Nudaurelia ω virus (NωV), infect Nudaurelia cytherea capensis (pine emperor moth) larvae. The absence of N. capensis laboratory colonies and tissue culture cell lines susceptible to virus infection have limited research on the biology of NβV and NωV because the availability of infectious virus is dependent upon sporadic outbreaks in the wild N. capensis populations. In September 2002, dead and dying N. capensis larvae exhibiting symptoms similar to those reported previously in other tetravirus infections were observed in a wild population in a pine forest in the Western Cape province of South Africa. We report here the isolation of three small insect viruses from this population over a period of three years. Transmission electron microscopy and serological characterization indicate that all three are tetra-like virus isolates. One isolate was shown by cDNA sequence analysis to be NβV, which was thought to have been extinct since 1985. The two other isolates are likely new tetraviruses, designated Nudaurelia ψ virus (NψV) and Nudaurelia ζ virus (NζV), which are morphologically and serologically related to NωV and NβV, respectively.
- Full Text:
- Date Issued: 2008