Biological control initiatives against Lantana camara L. (Verbenaceae) in South Africa : an assessment of the present status of the programme, and an evaluation of Coelocephalapion camarae Kissinger (Coleoptera: Brentidae) and Falconia intermedia (Distant) (Heteroptera: Miridae), two new candidate natural enemies for release on the weed
- Authors: Baars, Jan-Robert
- Date: 2003
- Subjects: Lantana camara Lantana camera -- South Africa Biological pest control agents -- South Africa Beetles -- South Africa Hemiptera -- South Africa Weeds -- Biological control -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5647 , http://hdl.handle.net/10962/d1005329
- Description: Lantana camara (lantana), a thicket-forming shrub, a number of different varieties of which were introduced into South Africa as ornamental plants but which has become a serious invasive weed. Conventional control measures for lantana are expensive and ineffective and it has therefore been targeted for biological control since 1961. To date, eleven biological control agent species have become established on lantana in South Africa. However, most agents persist at low densities and only occasionally impact plant populations. Three species regularly cause significant damage, but only reach sufficiently high numbers by midsummer after populations crash during the winter. Overall, the impact of the biological control programme on the weed is negligible and this has been ascribed to the poor selection of agents for release, the accumulation of native parasitoids, differences in insect preference for different varieties of the weed and variable climatic conditions over the weed’s range. This study suggests that the importance of varietal preferences has been over-estimated. A predictive bioclimatic modelling technique showed that most of the agents established in South Africa have a wide climatic tolerance and that the redistribution and importation of new climatypes of these agents will not improve the level of control. Additional agents are required to improve the biocontrol in the temperate conditions, and also to increase damage in the sub-tropical areas where most of the agents are established and where the weed retains its leaves year round. New candidate agents that possess biological attributes that favour a high intrinsic rate of increase, a high impact per individual and that improve the synchrony between the weed and the agent in climatic conditions that promote the seasonal leaflessness of plants should receive prior consideration. A survey in Jamaica indicated that additional biological control agents are available in the region of origin but that care should be taken to prioritise the most effective agents. The various selection systems currently available in weed biocontrol produce contradictory results in the priority assigned to candidate agents and a new selection system is proposed. The biology and host range of two new candidate natural enemies, the leaf-galling weevil, Coelocephalapion camarae and the leaf-sucking mirid, Falconia intermedia were investigated for the biocontrol of lantana. The studies indicated that these have considerable biocontrol potential, in that the weevil has a wide climatic tolerance and has the potential to survive the host leaflessness typical of temperate conditions, while the mirid has a high intrinsic rate of increase, and the potential for several generations a year. Both agents caused a high level of damage to the leaves, with the weevil galling the vascular tissue in the leaf-petiole and the mirid causing chlorotic speckling of the leaves. During laboratory trials both agents accepted indigenous species in the genus Lippia. However, under multiple choice conditions these agents showed a significant and strong oviposition preference for lantana. A risk assessment and post release field trials indicated that F. intermedia is likely to attack some Lippia species in the presence of lantana, but the levels of damage are predicted to be relatively low. A possible low incidence of damage to indigenous species was considered a justifiable ‘trade-off’ for the potentially marked impact on L. camara. Preference and performance studies on the two candidate agents suggested that most of the South African lantana varieties are suitable host plants. The mirid preferred certain varieties in multiple choice experiments, but this is unlikely to affect its impact under field conditions. Permission for release was accordingly sought for both species. Finally, the challenges facing the biological control programme and the potential for improving the control of L. camara in South Africa are considered.
- Full Text:
- Date Issued: 2003
- Authors: Baars, Jan-Robert
- Date: 2003
- Subjects: Lantana camara Lantana camera -- South Africa Biological pest control agents -- South Africa Beetles -- South Africa Hemiptera -- South Africa Weeds -- Biological control -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5647 , http://hdl.handle.net/10962/d1005329
- Description: Lantana camara (lantana), a thicket-forming shrub, a number of different varieties of which were introduced into South Africa as ornamental plants but which has become a serious invasive weed. Conventional control measures for lantana are expensive and ineffective and it has therefore been targeted for biological control since 1961. To date, eleven biological control agent species have become established on lantana in South Africa. However, most agents persist at low densities and only occasionally impact plant populations. Three species regularly cause significant damage, but only reach sufficiently high numbers by midsummer after populations crash during the winter. Overall, the impact of the biological control programme on the weed is negligible and this has been ascribed to the poor selection of agents for release, the accumulation of native parasitoids, differences in insect preference for different varieties of the weed and variable climatic conditions over the weed’s range. This study suggests that the importance of varietal preferences has been over-estimated. A predictive bioclimatic modelling technique showed that most of the agents established in South Africa have a wide climatic tolerance and that the redistribution and importation of new climatypes of these agents will not improve the level of control. Additional agents are required to improve the biocontrol in the temperate conditions, and also to increase damage in the sub-tropical areas where most of the agents are established and where the weed retains its leaves year round. New candidate agents that possess biological attributes that favour a high intrinsic rate of increase, a high impact per individual and that improve the synchrony between the weed and the agent in climatic conditions that promote the seasonal leaflessness of plants should receive prior consideration. A survey in Jamaica indicated that additional biological control agents are available in the region of origin but that care should be taken to prioritise the most effective agents. The various selection systems currently available in weed biocontrol produce contradictory results in the priority assigned to candidate agents and a new selection system is proposed. The biology and host range of two new candidate natural enemies, the leaf-galling weevil, Coelocephalapion camarae and the leaf-sucking mirid, Falconia intermedia were investigated for the biocontrol of lantana. The studies indicated that these have considerable biocontrol potential, in that the weevil has a wide climatic tolerance and has the potential to survive the host leaflessness typical of temperate conditions, while the mirid has a high intrinsic rate of increase, and the potential for several generations a year. Both agents caused a high level of damage to the leaves, with the weevil galling the vascular tissue in the leaf-petiole and the mirid causing chlorotic speckling of the leaves. During laboratory trials both agents accepted indigenous species in the genus Lippia. However, under multiple choice conditions these agents showed a significant and strong oviposition preference for lantana. A risk assessment and post release field trials indicated that F. intermedia is likely to attack some Lippia species in the presence of lantana, but the levels of damage are predicted to be relatively low. A possible low incidence of damage to indigenous species was considered a justifiable ‘trade-off’ for the potentially marked impact on L. camara. Preference and performance studies on the two candidate agents suggested that most of the South African lantana varieties are suitable host plants. The mirid preferred certain varieties in multiple choice experiments, but this is unlikely to affect its impact under field conditions. Permission for release was accordingly sought for both species. Finally, the challenges facing the biological control programme and the potential for improving the control of L. camara in South Africa are considered.
- Full Text:
- Date Issued: 2003
The suitability of Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae: Alticinae), as a biological control agent for Lantana camara L. in South Africa
- Authors: Williams, Hester Elizabeth
- Date: 2003
- Subjects: Lantana camara , Lantana camara -- South Africa , Biological pest control agents -- South Africa , Chrysomelidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5783 , http://hdl.handle.net/10962/d1005471 , Lantana camara , Lantana camara -- South Africa , Biological pest control agents -- South Africa , Chrysomelidae
- Description: Lantana camara Linnaeus (Verbenaceae), commonly known as lantana, is a highly invasive weed in many parts of the world. In South Africa it is naturalized in several provinces where it invades pastures, riverbanks, mountain slopes and valleys and commercial and natural forests, forming dense, impenetrable thickets. Chemical and mechanical control methods are expensive, labour intensive and provide only temporary relief as cleared areas are rapidly reinfested by seedlings and coppice growth. A biological control programme was initiated in South Africa in the 1960s, but despite the establishment of 11 agent species, it was considered to have had limited success. Several factors are thought to restrict the impact of the biocontrol agents. Firstly, L. camara occurs in a range of climatic regions, some of which are unsuitable for the establishment of agent species of tropical and subtropical origin. Secondly, L. camara is the result of hybridization between several Lantana species, forming a complex of hybridized and hybridizing varieties in the field, which match none of the Lantana species in the region of origin. This causes partial insect-host incompatibility, displayed as varietal preference. Thirdly, parasitism appears to have significantly reduced the effectiveness of several natural enemies. In spite of all these constraints, biological control has reduced invasion by L. camara by 26%. However, the weed is still very damaging and additional natural enemies are required to reduce infestations further. A flea-beetle species, Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae), was collected from several sites in the humid subtropical and tropical regions of Mexico, and imported into quarantine in South Africa and studied as a potential biocontrol agent for L. camara. Favourable biological characteristics of this beetle included long-lived adults, several overlapping generations per year, and high adult and larval feeding rates. Observations from the insect’s native range and studies in South Africa suggest that A. extrema would probably be more suited to the subtropical, rather than the temperate areas in South Africa. Laboratory impact studies indicated that feeding damage by A. extrema larvae, over a period spanning the larval stage (16 to 20 days), reduced the above-ground biomass of L. camara plants by up to 29%. Higher larval populations resulted in a higher reduction of biomass. Varietal preference and suitability studies indicated that A. extrema exhibits a degree of varietal preference under laboratory conditions, with one of the white pink L. camara varieties proving the most suitable host. This variety is one of the most damaging varieties in South Africa and is particularly widespread in Mpumalanga Province. Although A. extrema proved to be damaging to L. camara, laboratory host range trials showed it to be an oligophagous species, capable of feeding and developing on several non-target species, especially two native Lippia species (Verbenaceae). The host suitability of these species was marginally lower than that of L. camara and the potential risk to these indigenous species was deemed to be too high to warrant release. It was therefore recommended that A. extrema not be considered for release in South Africa.
- Full Text:
- Date Issued: 2003
- Authors: Williams, Hester Elizabeth
- Date: 2003
- Subjects: Lantana camara , Lantana camara -- South Africa , Biological pest control agents -- South Africa , Chrysomelidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5783 , http://hdl.handle.net/10962/d1005471 , Lantana camara , Lantana camara -- South Africa , Biological pest control agents -- South Africa , Chrysomelidae
- Description: Lantana camara Linnaeus (Verbenaceae), commonly known as lantana, is a highly invasive weed in many parts of the world. In South Africa it is naturalized in several provinces where it invades pastures, riverbanks, mountain slopes and valleys and commercial and natural forests, forming dense, impenetrable thickets. Chemical and mechanical control methods are expensive, labour intensive and provide only temporary relief as cleared areas are rapidly reinfested by seedlings and coppice growth. A biological control programme was initiated in South Africa in the 1960s, but despite the establishment of 11 agent species, it was considered to have had limited success. Several factors are thought to restrict the impact of the biocontrol agents. Firstly, L. camara occurs in a range of climatic regions, some of which are unsuitable for the establishment of agent species of tropical and subtropical origin. Secondly, L. camara is the result of hybridization between several Lantana species, forming a complex of hybridized and hybridizing varieties in the field, which match none of the Lantana species in the region of origin. This causes partial insect-host incompatibility, displayed as varietal preference. Thirdly, parasitism appears to have significantly reduced the effectiveness of several natural enemies. In spite of all these constraints, biological control has reduced invasion by L. camara by 26%. However, the weed is still very damaging and additional natural enemies are required to reduce infestations further. A flea-beetle species, Alagoasa extrema Jacoby (Coleoptera: Chrysomelidae), was collected from several sites in the humid subtropical and tropical regions of Mexico, and imported into quarantine in South Africa and studied as a potential biocontrol agent for L. camara. Favourable biological characteristics of this beetle included long-lived adults, several overlapping generations per year, and high adult and larval feeding rates. Observations from the insect’s native range and studies in South Africa suggest that A. extrema would probably be more suited to the subtropical, rather than the temperate areas in South Africa. Laboratory impact studies indicated that feeding damage by A. extrema larvae, over a period spanning the larval stage (16 to 20 days), reduced the above-ground biomass of L. camara plants by up to 29%. Higher larval populations resulted in a higher reduction of biomass. Varietal preference and suitability studies indicated that A. extrema exhibits a degree of varietal preference under laboratory conditions, with one of the white pink L. camara varieties proving the most suitable host. This variety is one of the most damaging varieties in South Africa and is particularly widespread in Mpumalanga Province. Although A. extrema proved to be damaging to L. camara, laboratory host range trials showed it to be an oligophagous species, capable of feeding and developing on several non-target species, especially two native Lippia species (Verbenaceae). The host suitability of these species was marginally lower than that of L. camara and the potential risk to these indigenous species was deemed to be too high to warrant release. It was therefore recommended that A. extrema not be considered for release in South Africa.
- Full Text:
- Date Issued: 2003
- «
- ‹
- 1
- ›
- »