Development of Cactoblastis cactorum (Berg)(Lepidoptera: pyralidae) on six north American Opuntia species
- Authors: Mafokoane, L D , Zimmermann, Helmuth G , Hill, Martin P
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451346 , vital:75042 , https://hdl.handle.net/10520/EJC32740
- Description: Cactoblastis cactorum (Berg) (Lepidoptera : Pyralidae) has been used as a biological control agent of several Opuntia species around the world and is widely assumed to be a generalist on host plants within the genus Opuntia. The recent arrival and spread of C. cactorum on the North American mainland has raised concerns for the native species of Opuntia that are being utilized as hosts by the moth. To confirm that C. cactorum is a threat to a wide range of Opuntia species in North America, the host range of the moths was scrutinized in South Africa, where larval development could be monitored on several Opuntia species under natural conditions. Development was monitored on Opuntia ficus-indica L. Miller, O. engelmannii Salm-Dyke, O. fulgida Englm, O. imbricata (Haworth) de Candolle, O. stricta Haworth and O. leucotrichta DC. Larval survival, egg to pupation, was highest on O. ficus-indica (79.2%) followed by O. engelmannii (57.5 %), O. stricta (55.0 %), O. leucotrichta (29.2 %), O. fulgida (24.2 %) and O. imbricata (16.7 %). Male and female pupal mass was highest, and duration of development shortest on O. ficus-indica. In adult multi-choice oviposition trials, females laid significantly more egg sticks on O. ficus-indica than on the other species. Although O. ficusindica is the preferred host for C. cactorum in South Africa, the moth is nevertheless able to utilize several other species of Opuntia as hosts.
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Impact of nutrients and herbivory by Eccritotarsus catarinensis on the biological control of water hyacinth, Eichhornia crassipes
- Authors: Coetzee, Julie A , Byrne, Marcus J , Hill, Martin P
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6945 , http://hdl.handle.net/10962/d1011973 , https://orcid.org/0000-0003-0579-5298
- Description: Many water hyacinth infestations in South Africa are the symptom of eutrophication, and as a result, biological control of this weed is variable. This study examined the effects of herbivory by the mirid, Eccritotarsus catarinensis, on water hyacinth grown at high, medium and low nitrogen (N) and phosphorus (P) nutrient concentrations. Water nutrient concentration appears to be the overriding factor affecting plant growth parameters of water hyacinth plants—at high nutrient concentrations, leaf and daughter plant production were more than double than at low nutrient concentrations, while stem length was twice as great at high nutrient concentrations compared to low concentrations. Chlorophyll content was also twice as high at high nutrient concentrations than low concentrations. Conversely, flower production at high nutrient concentrations was less than half that at low concentrations. Herbivory by E. catarinensis did not have as great an effect on water hyacinth vigour as nutrient concentration did, although it significantly reduced the production of daughter plants by 23 ± 9%, the length of the second petiole by 13 ± 5%, and chlorophyll content of water hyacinth leaves by 15 ± 6%. In terms of insect numbers, mirids performed better on plants grown under medium nutrient conditions (99 ± 28 S.E.), compared to high nutrient concentrations (52 ± 27 S.E.), and low nutrient concentrations (25 ± 30 S.E.). Thus, these results suggest that the fastest and most significant reduction in water hyacinth proliferation would be reached by lowering the water nutrient concentrations, and herbivory by E. catarinensis alone is not sufficient to reduce all aspects of water hyacinth vigour, especially at very high nutrient concentrations.
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The biology and laboratory host range of the weevil, Listronotus marginicollis (Hustache)(Coleoptera: Curculionidae), a natural enemy of the invasive aquatic weed, parrot's feather, Myriophyllum aquaticum (Velloso) Verde (Haloragaceae).
- Authors: Oberholzer, I G , Mafokoane, D L , Hill, Martin P
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451555 , vital:75059 , https://hdl.handle.net/10520/EJC32727
- Description: Myriophyllum aquaticum (Velloso) Verde (Haloragaceae), parrot's feather, is a rooted aquatic plant, with stems of up to 3 m long and leafy terminal shoots. The plant roots in shallow water to form a dense tangle of stems and roots. The shoots emerge 200-500 mm above the water surface (Cilliers 1999). The leaves of the plant are feathery and occur in whorls. The stem-boring weevil, Listronotus marginicollis (Hustache) (Coleoptera: Curculionidae), was next considered as the most promising additional biological control agent for the control of M. aquaticum in southern Africa (Cilliers 1999).
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The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp
- Authors: Wilson, J R U , Ajuonub, O , Center, R D , Hill, Martin P , Julien, M H , Katagira, F F , Neuenschwander, P , Njoka, S W , Ogwang, J , Reeder, R H , Van, T
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6927 , http://hdl.handle.net/10962/d1011918 , https://orcid.org/0000-0003-0579-5298
- Description: There has been some debate recently about the cause of the decline of water hyacinth on Lake Victoria. While much of this evidence points to classical biological control as the major factor, the El Niño associated weather pattern of the last quarter of 1997 and the first half of 1998 has confused the issue. We argue first that the reductions in water hyacinth on Lake Victoria were ultimately caused by the widespread and significant damage to plants by Neochetina spp., although this process was increased by the stormy weather associated with the El Niño event; second that increased waves and current on Lake Victoria caused by El Niño redistributed water hyacinth plants around the lake; and third that a major lake-wide resurgence of water hyacinth plants on Lake Victoria has not occurred and will not occur unless the weevil populations are disrupted. We conclude that the population crash of water hyacinth on Lake Victoria would not have occurred in the absence of the weevils, but that it may have been hastened by stormy weather associated with the El Niño event.
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The relationship between female pupal mass and fecundity of Gratiana spadicea (Klug, 1829)(Coleoptera: Chrysomelidae)
- Authors: Czypionka, K , Hill, Martin P
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451568 , vital:75060 , https://hdl.handle.net/10520/EJC32729
- Description: In the early 1900s Solanum sisymbriifolium Lamarck (Solanaceae), commonly known as dense thorned bitter apple and previously referred to as wild tomato, was introduced into southern Africa and has since become an invasive weed (Hill and Hulley 1995, 1996). In 1994 a chrysomelid beetle, Gratiana spadicea (Klug, 1829) (Coleoptera : Chrysomelidae), was introduced as a biological control agent against the weed (Hill and Hulley 1995). Prior to its release, various specificity tests were conducted to identify the potential host range of this agent. These included larval survival and adult choice and no-choice tests on several native and commercial Solanum species. These specificity tests generally identify the potential host range of an agent accurately, but fail to predict the magnitude of non-target risks in the field (Wan and Harris 1997; Louda et al. 2003).
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