The effect of habitat management on the impact of Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae), on Pompom weed in South Africa Phuluso Mudau 2019 School of Animal, Plant and Environmental Sciences A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science, Johannesburg, South Africa. May 2019 Declaration I declare that this Dissertation is my own work. It is being submitted for the Degree of Master of Science at the University of the Witwatersrand, Johannesburg. It has not been submitted by me before for any other degree, diploma or examination at any other University or tertiary institution. Phuluso Mudau May 2019 Supervisors: Prof. Marcus J. Byrne (University of the Witwatersrand) Prof. Ed T.F. Witkowski (University of the Witwatersrand) Ms. L. van der Westhuizen (Agricultural Research Council- Plant Protection Research) 1 Dedication This Dissertation is dedicated to my dad (Takalani Mudau), mom (Gladys Mudau), and my one and only brother Tumelo Mudau. Thank you for your support. 2 Acknowledgements I would like to thank my supervisors Prof. Marcus J. Byrne, Ms. Liame van der Westhuizen and Prof. Ed T.F. Witkowski for their supervision, guidance and constructive comments towards completion of this project. I am also grateful to Phillimon Mpedi for his advice and guidance on propagation and culturing of pompom weed and the thrips biocontrol agent. I would also like to thank the Waterkloof Airforce Base staff members, in particular Major Mariska Vogel, Thato Chauke and Coert Theron for always assisting me in gaining access to the base. Macphee Madzivhe, Sanele Mtetwa and Joe Venturi thank you for assisting me with field work and driving me to the base and Bonginkosi Hlalukane for always being there for me when I needed field equipment. To the Biocontrol lab; Sipho Mbonani, Lerato Molekoa, Macphee Madzivhe, Lyriche Drude, Sanele Mtetwa, Kuda Musengi, Prisca Thobejane, Bongkuhle Mabuya, Lusungu Nkoma, Abubakar Bello, Zanele Machimane, Tumi Mathige, Guelor Mayonde, Amy Burness, Peter Kgampe, Tshuxekani Maluleke, Jeanne Mukarugwiro, Naweji Katembo, Archie Sassa, Danica Marlin, Solomon Newete, Joe Venturi and Blair Cowie thank you for your support and company. I would like to thank the NRF for funding my project. I am also grateful to FEENIX crowd funding for clearing my historical debt that threatened my stay at the University of the Witwatersrand. Would also like to thank South African Weather Service (SAWS) for the temperature data. To my mom and dad, thank you for the support and for always encouraging me to work hard. 3 Abstract Campuloclinium macrocephalum (Less.) DC. (Asteraceae), is an invasive perennial herb, mainly in the grassland biome of South Africa, commonly known as pompom weed. It is native to South and Central America. Since the 1980s it has invaded wetlands, roadsides and grasslands and poses a significant environmental threat, such as displacement of indigenous vegetation, reduction in grazing capacity of farms and game reserves because of its unpalatability to wildlife and livestock. Given the shortcomings of chemical and mechanical control methods, biological control is considered the most sustainable and environmentally friendly method of controlling some invasive plants such as pompom weed. Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripinae) is a stem and leaf deforming biological control agent released against C. macrocephalum in 2013. During laboratory impact studies L. tractabilis was found to significantly reduce the growth of C. macrocephalum. Young and regrowth plants that were inoculated with thrips demonstrated a significant reduction in leaf production, biomass and height compared to the control plants, with a reduced floral production. Light intensity is one of the factors that has been found to affect plant growth and population structure and consequently that of other living organisms, including insects. Exposure to light alters leaf quality, such as phenolic and nitrogen contents, water content and structural defences. Plants that are exposed to high light are often less palatable, making herbivores more likely to colonise plants in the shade. Many studies have observed increased rates of herbivory on plants in shaded environments, while conversely other studies found increased herbivory on plants in full sun. The first aim of this study was to compare the impact of L. tractabilis on the growth of C. macrocephalum in sunny (areas with short, mown grass) versus shaded environments (areas with long unmown grass). In this study, the number of adults, nymphs and eggs of L. tractabilis were found to be significantly higher in the sunny environment, which resulted in 78% of C. macrocephalum plants with deformed growth (plants with altered apical shoot tips), as well as a 64% reduction in plant height and a 74% reduction in the proportion of plants with flowers. Therefore, an early season mowing of C. macrocephalum in invaded veld, has the potential to enhance the performance of the biocontrol agent, L. tractabilis in reducing the vigour and reproduction of pompom weed. 4 The second aim of this study was to investigate the life stages of L. tractabilis that overwinter and assess their impact on the fleshy rootstocks of C. macrocephalum. In the southern hemisphere, perennial plants such as C. macrocephalum respond to seasonal reductions in rainfall with dieback to below-ground plant tissue during the dry and cold winter from May onwards followed by regrowth from the fleshy rootstocks in spring (October) at the commencement of the new growing (rainy) season. Liothrips tractabilis was found to display a similar pattern by moving to the underground plant parts of C. macrocephalum in winter, only to reappear in spring on the above-ground shoot regrowth. Adults of L. tractabilis were found to be the main life stage that overwinter on the plant roots, with only 4% of L. tractabilis individuals being nymphs. Liothrips tractabilis had no significant effect on the number, mass, thickness or length of the weed’s roots during the dry season. Therefore, L. tractabilis is only effective in controlling C. macrocephalum above-ground growth during the growing season. The effect of habitat management such as mowing enhanced the impact of L. tractabilis on C. macrocephalum. Overwintering L. tractabilis adults were most frequently found at the 4-6 cm depth from the soil surface (52%), which suggests that they could survive the typical Highveld winter fires. Thus, integrated control of C. macrocephalum using both fire and the biocontrol agent Liothrips tractabilis is feasible and should be trialed. Keywords: Alien invasive plants, impact, insect development, light intensity, mowing, overwintering, plant damage 5 Table of contents Declaration............................................................................................................................................. 1 Dedication .............................................................................................................................................. 2 Acknowledgements ............................................................................................................................... 3 Abstract .................................................................................................................................................. 4 CHAPTER 1: ....................................................................................................................................... 12 General introduction .......................................................................................................................... 12 1.1 Invasive plants ........................................................................................................................... 12 1.2 Management and Biological control ........................................................................................ 13 1.3 Factors affecting establishment of biological control agents ................................................. 14 1.4 Campuloclinium macrocephalum and its native and invasive distributions......................... 15 1.5 Management of Campuloclinium macrocephalum .................................................................. 17 1.6 Biological control of Campuloclinium macrocephalum .......................................................... 18 1.7 Liothrips tractabilis .................................................................................................................... 19 1.8 Developmental rates of insects and overwintering ................................................................. 21 1.9 Aims and objectives .................................................................................................................. 22 CHAPTER 2: ....................................................................................................................................... 23 Does early season mowing increase the impact of Liothrips tractabilis on Campuloclinium macrocephalum during the growing season? .................................................................................... 23 Abstract ................................................................................................................................................ 23 2.1 Introduction ..............................................................................................................................