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  • 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.

    THESIS

    Submitted in fulfillment of the

    requirements for the degree of

    DOCTOR OF PHILOSOPHY

    of Rhodes University

    by

    JAN-ROBERT BAARS

    January 2002

  • ii

    ABSTRACT

    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.

  • iii

    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.

  • iv

    FRONTISPIECE

    Top row (Left to Right): Lantana camara (lantana); state of L. camara in dry and cold

    winter conditions; Flower colour of South African lantana varieties.

    Second row (Left to Right): Falconia intermedia impact on lantana (Tzaneen, South

    Africa); F. intermedia nymph and adult; feeding damage on lantana seedlings.

    Bottom row (Left to Right): Coelocephalapion camarae petiole galls on lantana; L.

    camara in native range (Mexico); No-choice host-specificity trials (Pretoria, South

    Africa).

  • v

    PUBLICATIONS ARISING FROM THIS STUDY

    Parts of this thesis have already been accepted for publication:

    Baars, J-R. and Neser, S. 1999. Past and present initiatives on the biological control of

    Lantana camara (Verbenaceae) in South Africa. In: T. Olckers and M.P. Hill

    (eds.). Biological Control of Weeds in South Africa (1990-1998). African

    Entomology Memoir 1: 21-33.

    Baars, J-R. 2000. Emphasising behavioural host range: the key to resolving ambiguous

    host specificity results on Lantana camara L. (Verbenaceae). In: N.R. Spencer

    (ed.). Proceedings of the Xth International Symposium on Biological Control of

    Weeds. July 2-5 1999, Montana State University, Bozeman, Montana, USA. pp.

    887-896.

    Baars, J-R. 2000. Biology and host range of Falconia intermedia (Hemiptera: Miridae), a

    potentially damaging natural enemy of Lantana camara in South Africa. In: N.R.

    Spencer (ed.). Proceedings of the Xth International Symposium on Biological

    Control of Weeds. July 2-5 1999, Montana State University, Bozeman, Montana,

    USA. p. 673.

    Baars, J-R. 2000. A cure for lantana at last? Plant Protection News 57: 8-11.

    Baars, J-R. and Heystek, F. 2001. Potential contribution of the petiole galling weevil,

    Coelocephalapion camarae Kissinger, to the biocontrol of Lantana camara L. In:

    T. Olckers and D.J. Brothers (eds.). Proceedings of the Thirteenth Entomological

    Congress. July 2-5, Pietermaritzburg, South Africa. p. 79.

    Baars, J-R. submitted. Geographic range, impact, and parasitism of lepidopteran species

    associated with the invasive weed Lantana camara in South Africa. Biological

    Control.

    Baars, J-R., Urban, A.J. and Hill, M.P. submitted. Biology, host range, and risk

    assessment supporting release in Africa of Falconia intermedia (Heteroptera:

    Miridae), a new biocontrol agent for Lantana camara. Biological Control.

    Baars, J-R. and Heystek, F. submitted. Geographical range and impact of five biocontrol

    agents established on Lantana camara in South Africa. BioControl.

  • vi

    ACKNOWLEDGEMENTS

    I owe a great deal of gratitude to both of my supervisors, Professor P.E. Hulley and Dr

    M.P. Hill for their support and guidance throughout this project. I thank them both for

    constructive comments on earlier drafts of the thesis. I thank Martin for teaching me how

    to be effective in a research project, and for his enthusiasm and above all his friendship.

    I appreciate all the time and effort Drs Terry Olckers, Alan Urban, Helmuth

    Zimmermann, Stefan Neser and other staff of the Plant Protection Research Institute have

    put into reviewing parts of this thesis and thank them for their suggestions and criticisms.

    Thanks are also due to the following people:

    Alan Urban for his frequent reassurance, enthusiasm and support for my research, and for

    his valuable insights into scientific methodology, writing style and attention to detail;

    Terry Olckers for his dedicated attention to my manuscripts and his patience while

    helping me refine my scientific writing skills; Mark Robertson (Rhodes University) for

    conducting the predictive distribution modelling technique, and providing comments;

    Lesley Henderson (PPRI) for supplying SAPIA distribution maps; Marie Smith and Liesl

    Morey (ARC-Biometry Unit) for their advice and assistance in the statistical analysis of

    my results; the researchers at the National Collection of Insects, particularly Gerard

    Prinsloo and Riaan Stals, and David Kissinger (Linda Loma, U.S.A.), Martin Kruger

    (Transvaal Museum), David Barraclough (Natal Museum), T. Henry (Systematic

    Entomology Laboratory, U.S.D.A.) and Don Davis (Smithsonian National Museum of

    Natural History) for their taxonomic services; the staff of the Plant Protection Research

    Institute for valuable dis

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