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 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. ii 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. iii 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). iv 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. v 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 discussions and support; Zolliele Duze (Working for Water Programme, Department of Water Affairs and Forestry), Hardi Oberholzer, Hester Williams (both PPRI) and Tammy Smith (Rhodes University) for their field assistance; Wendy Forno, Ricardo Segura and Moises Martinez (CSIRO, Australia) for their assistance during field surveys in Mexico; Elisabeth Retief (National Botanical Institute) and Roger Sanders (Botanical Research Institute of Texas) for identifying plant material; and Wiekus Botha (WfW, Tzaneen) for his dedication to the mass-rearing of lantana vi biocontrol agents. I am especially indebted to Fritz Heystek, who not only gave his continuous assistance during my research, but also provided unending amusement and a great friendship. I thank Sarah, my wife and friend for her love and support throughout the project and especially for her patience and reassurance during the write