The role of nutrients in the biological control of water lettuce, Pistia stratiotes lamarck (Araceae) by the leaf-feeding weevil, Neohydronomus affinis Hustache (Coleoptera: Curculionidae) with particular reference to eutrophic conditions
- Authors: Moore, Gareth Ryan
- Date: 2006
- Subjects: Water lettuce -- Biological control , Araceae , Beetles , Curculionidae , Weeds -- Biological control , Pests -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5759 , http://hdl.handle.net/10962/d1005447 , Water lettuce -- Biological control , Araceae , Beetles , Curculionidae , Weeds -- Biological control , Pests -- Biological control
- Description: Water lettuce, Pistia stratiotes Lamarck (Araceae) is a South American plant that has the potential to be a very damaging and important aquatic weed in many tropical countries, including South Africa. It has the potential to rapidly multiply vegetatively and completely cover watercourses in a very short space of time outside of its natural range under ideal conditions and without its natural enemies. In such instances, the weed may cause hindrances to water transport and fishing, increasing chances of malaria, as well as affecting the natural ecology of the system. Water lettuce can also set seed, which may lay dormant for long periods, germinating when conditions are favourable. It is therefore very necessary to adopt control methods against the weed where it is a problem. However, water lettuce has also been effectively and completely controlled in many countries by the leaf-feeding weevil, Neohydronomus affinis Hustache. High nutrient levels in the form of nitrates and phosphates have been shown to have largely negative effects on biological control in several studies, with control being incomplete or taking longer than in similar areas with lower nutrient levels. The effectiveness of N. affinis on the biological control of water lettuce was investigated in a laboratory study, growing P. stratiotes plants with and without insects at different nutrient concentrations. In these studies biological control of water lettuce with N. affinis was found to be complete under eutrophic nutrient conditions, although control took longer when higher nutrient levels were tested. A field site study was conducted at a sewage settlement pond in Cape Recife Nature Reserve near Port Elizabeth, South Africa. This highly eutrophic system was used as a field example for the effectiveness of biocontrol of P. stratiotes by N. affinis under eutrophic conditions. The weevils at Cape Recife caused a massive and rapid crash in the percentage coverage of the weed, from 100% in May 2003, to approximately 0.5 % in September 2003. Plant growth parameters were also found to decrease considerably in size correspondingly with this crash from May 2003 until spring 2003. Plant size only again started to increase gradually but steadily through spring 2003 and into summer. In the laboratory studies, the fecundity of weevils was shown to be much higher on plants grown under higher nutrient concentrations than on plants grown in lower nutrient concentrations. The results from the wing-muscle analysis under different nutrient concentrations were not easy to interpret, and there were few differences in wing muscle state between most of the concentrations. From these findings it is suggested that nutrient concentration, particularly high levels of nitrates and phosphates is not a limiting factor in terms of effective biological control of P. stratiotes with N. affinis, but that under high nutrient conditions biological control might take longer.
- Full Text:
- Date Issued: 2006
- Authors: Moore, Gareth Ryan
- Date: 2006
- Subjects: Water lettuce -- Biological control , Araceae , Beetles , Curculionidae , Weeds -- Biological control , Pests -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5759 , http://hdl.handle.net/10962/d1005447 , Water lettuce -- Biological control , Araceae , Beetles , Curculionidae , Weeds -- Biological control , Pests -- Biological control
- Description: Water lettuce, Pistia stratiotes Lamarck (Araceae) is a South American plant that has the potential to be a very damaging and important aquatic weed in many tropical countries, including South Africa. It has the potential to rapidly multiply vegetatively and completely cover watercourses in a very short space of time outside of its natural range under ideal conditions and without its natural enemies. In such instances, the weed may cause hindrances to water transport and fishing, increasing chances of malaria, as well as affecting the natural ecology of the system. Water lettuce can also set seed, which may lay dormant for long periods, germinating when conditions are favourable. It is therefore very necessary to adopt control methods against the weed where it is a problem. However, water lettuce has also been effectively and completely controlled in many countries by the leaf-feeding weevil, Neohydronomus affinis Hustache. High nutrient levels in the form of nitrates and phosphates have been shown to have largely negative effects on biological control in several studies, with control being incomplete or taking longer than in similar areas with lower nutrient levels. The effectiveness of N. affinis on the biological control of water lettuce was investigated in a laboratory study, growing P. stratiotes plants with and without insects at different nutrient concentrations. In these studies biological control of water lettuce with N. affinis was found to be complete under eutrophic nutrient conditions, although control took longer when higher nutrient levels were tested. A field site study was conducted at a sewage settlement pond in Cape Recife Nature Reserve near Port Elizabeth, South Africa. This highly eutrophic system was used as a field example for the effectiveness of biocontrol of P. stratiotes by N. affinis under eutrophic conditions. The weevils at Cape Recife caused a massive and rapid crash in the percentage coverage of the weed, from 100% in May 2003, to approximately 0.5 % in September 2003. Plant growth parameters were also found to decrease considerably in size correspondingly with this crash from May 2003 until spring 2003. Plant size only again started to increase gradually but steadily through spring 2003 and into summer. In the laboratory studies, the fecundity of weevils was shown to be much higher on plants grown under higher nutrient concentrations than on plants grown in lower nutrient concentrations. The results from the wing-muscle analysis under different nutrient concentrations were not easy to interpret, and there were few differences in wing muscle state between most of the concentrations. From these findings it is suggested that nutrient concentration, particularly high levels of nitrates and phosphates is not a limiting factor in terms of effective biological control of P. stratiotes with N. affinis, but that under high nutrient conditions biological control might take longer.
- Full Text:
- Date Issued: 2006
Interactions between three biological control agents of water hyacinth, Eichhornia crassipes (Mart.) Solms (Pontederiaceae) in South Africa
- Authors: Petela, Nomvume
- Date: 2018
- Subjects: Water hyacinth -- South Africa , Water hyacinth -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Curculionidae , Delphacidae , Miridae , Neochetina eichhorniae Warner , Megamelus scutellaris Berg , Eccritotarsus eichhorniae Henry
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60676 , vital:27814
- Description: Water hyacinth, Eichhomia crassipes (Mart.) Solms (Pontederiaceae) is a free-floating perennial weed that is regarded as the worst aquatic weed in the world because of its negative impacts on aquatic ecosystems. It is native to the Amazon Basin of South America, but since the late 1800s has spread throughout the world. The first record of the weed in South Africa was noted in 1908 on the Cape Flats and in KwaZulu-Natal, but it is now dispersed throughout the country. Mechanical and chemical control methods have been used against the weed, but biological control is considered the most cost-effective, sustainable and environmentally friendly intervention. Currently, nine biological control agents have been released against water hyacinth in South Africa, and Neochetina eichhorniae Warner (Coleoptera: Curculionidae) is used most widely to control it. However, in some sites, water hyacinth mats have still not been brought under control because of eutrophic waters and cool temperatures. It was therefore necessary to release new biological control agents to complement the impact of N. eichhorniae. Megamelus scutellaris Berg (Hemiptera: Delphacidae) was released in 2013, but little is known about how it interacts with other agents already present in South Africa. It is likely to compete with the established biological control agent, Eccritotarsus eichhorniae Henry (Heteroptera: Miridae), because they are both sap suckers. On the other hand, N. eichhorniae is the most widespread and thus the most important biological control agent for water hyacinth. The aim of this study, then, was to determine the interactions between the two sap-sucking agents in South Africa that presumably occupy similar niches on the plant, and the interaction between M. scutellerais and N. eichhorniae, the most widely distributed and abundant agent in South Africa. Three experiments were conducted at the Waainek Research Facility at Rhodes University, Grahamstown, Eastern Cape, South Africa. Plants were grown for two weeks and insect species were inoculated singly or in combination. Water hyacinth, plant growth parameters and insect parameters were measured every 14 days for a period of 12 weeks. The results of the study showed that feeding by either E. eichhorniae or M. scutellaris had no effect on the feeding of the other agent. Both agents reduced all the measured plant growth parameters equally, either singly or in combination (i.e. E. eichhorniae or M. scutellaris alone or together). The interaction between the two agents appears neutral and agents are likely to complement each other in the field. Prior feeding by E. eichhorniae or M. scutellaris on water hyacinth did not affect the subsequent feeding by either agent. Megamelus scutellaris prefers healthy fresh water hyacinth plants. In addition, planthoppers performed best in combination with the weevil, especially on plants with new weevil feeding scars. The results of the study showed that M. scutellaris is compatible with other biological control agents of water hyacinth that are already established in South Africa. Therefore, the introduction of M. scutellaris may enhance the biological control of water hyacinth in South Africa.
- Full Text:
- Date Issued: 2018
- Authors: Petela, Nomvume
- Date: 2018
- Subjects: Water hyacinth -- South Africa , Water hyacinth -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Curculionidae , Delphacidae , Miridae , Neochetina eichhorniae Warner , Megamelus scutellaris Berg , Eccritotarsus eichhorniae Henry
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60676 , vital:27814
- Description: Water hyacinth, Eichhomia crassipes (Mart.) Solms (Pontederiaceae) is a free-floating perennial weed that is regarded as the worst aquatic weed in the world because of its negative impacts on aquatic ecosystems. It is native to the Amazon Basin of South America, but since the late 1800s has spread throughout the world. The first record of the weed in South Africa was noted in 1908 on the Cape Flats and in KwaZulu-Natal, but it is now dispersed throughout the country. Mechanical and chemical control methods have been used against the weed, but biological control is considered the most cost-effective, sustainable and environmentally friendly intervention. Currently, nine biological control agents have been released against water hyacinth in South Africa, and Neochetina eichhorniae Warner (Coleoptera: Curculionidae) is used most widely to control it. However, in some sites, water hyacinth mats have still not been brought under control because of eutrophic waters and cool temperatures. It was therefore necessary to release new biological control agents to complement the impact of N. eichhorniae. Megamelus scutellaris Berg (Hemiptera: Delphacidae) was released in 2013, but little is known about how it interacts with other agents already present in South Africa. It is likely to compete with the established biological control agent, Eccritotarsus eichhorniae Henry (Heteroptera: Miridae), because they are both sap suckers. On the other hand, N. eichhorniae is the most widespread and thus the most important biological control agent for water hyacinth. The aim of this study, then, was to determine the interactions between the two sap-sucking agents in South Africa that presumably occupy similar niches on the plant, and the interaction between M. scutellerais and N. eichhorniae, the most widely distributed and abundant agent in South Africa. Three experiments were conducted at the Waainek Research Facility at Rhodes University, Grahamstown, Eastern Cape, South Africa. Plants were grown for two weeks and insect species were inoculated singly or in combination. Water hyacinth, plant growth parameters and insect parameters were measured every 14 days for a period of 12 weeks. The results of the study showed that feeding by either E. eichhorniae or M. scutellaris had no effect on the feeding of the other agent. Both agents reduced all the measured plant growth parameters equally, either singly or in combination (i.e. E. eichhorniae or M. scutellaris alone or together). The interaction between the two agents appears neutral and agents are likely to complement each other in the field. Prior feeding by E. eichhorniae or M. scutellaris on water hyacinth did not affect the subsequent feeding by either agent. Megamelus scutellaris prefers healthy fresh water hyacinth plants. In addition, planthoppers performed best in combination with the weevil, especially on plants with new weevil feeding scars. The results of the study showed that M. scutellaris is compatible with other biological control agents of water hyacinth that are already established in South Africa. Therefore, the introduction of M. scutellaris may enhance the biological control of water hyacinth in South Africa.
- Full Text:
- Date Issued: 2018
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