IMPACTS OF CLIMATE VARIABILITY ON STEMBORERS-NATURAL ENEMIES TROPHIC LEVEL INTERACTION: IMPLICATIONS FOR BIOLOGICAL CONTROL UNDER GLOBAL CHANGE by REYARD MUTAMISWA Reg. No: 13100028 BSc Natural Resources Management & Agriculture (Hons) Crop Production & Horticulture (MSU), MSc Tropical Entomology (UZ) Department of Biological Sciences and Biotechnology, Faculty of Science, Botswana International University of Science and Technology [email protected] A Thesis Submitted to the Faculty of Science in Partial Fulfilment of the Requirements for the Doctor of Philosophy in Biological Sciences of BIUST Supervisor: Dr Casper Nyamukondiwa Department of Biological Sciences and Biotechnology, Faculty of Science, BIUST [email protected] December, 2017 i DECLARATION AND COPYRIGHT I, REYARD MUTAMISWA, declare that this thesis is my own original work and that it has not been presented and will not be presented to any other university for a similar or any other degree award. Signature: This thesis is copyright material protected under the Berne Convention, the Copyright Act of 1999 and other international and national enactments, in that behalf, on intellectual property. It must not be reproduced by any means, in full or in part, except for short extracts in fair dealing; for researcher private study, critical scholarly review or discourse with an acknowledgement, without the written permission of the office of the Provost, on behalf of both the author and BIUST ii CERTIFICATION The undersigned certifies that he has read and hereby recommends for acceptance by the Faculty of Science a thesis titled: Impacts of Climate Variability on Stemborers-Natural Enemies Trophic Level Interaction: Implications for Biological Control Under Global Change, in fulfilment of the requirements for the degree of Doctor of Philosophy in Biological Sciences (Applied Entomology) of BIUST. ………………………………… Dr. Casper Nyamukondiwa (Supervisor) Date: 03 February 2018 iii DEDICATION This thesis is dedicated to my family and my mom. Your prayers, support and love during the course of this study are highly appreciated. iv ACKNOWLEDGEMENTS Firstly I would like to thank Almighty God for giving me strength and wisdom throughout this study. Secondly, my sincere gratitude goes to my supervisor Dr. Casper Nyamukondiwa for his unwavering support, guidance and mentorship throughout the study period. This research would not have been possible without your patience, excellent supervision and encouragement. I sincerely thank Botswana International University of Science and Technology (BIUST) for granting me this opportunity to pursue my studies and financial support. Special thanks also go to International Centre for Insect Physiology and Ecology (ICIPE), South African Sugarcane Research Institute (SASRI) for provision of insects that I used for the entire duration of this study. I would also like to extend my gratitude to Ministry of Agriculture, Botswana for provision of import permits for the insects that I used in this research. I also express my sincere gratitude to Dr. Frank Chidawanyika for editing and advice in the write up and several anonymous referees for the constructive comments on earlier versions of different chapters of this thesis. Many thanks to my laboratory colleagues Eva Moeng, Honest Machekano, Mphoeng Ofithile, Mmabaledi Buxton, Nonofo Gotcha, Rebaone Motswagole and Biological Sciences department technical team for their support throughout my study. Finally, I also extend my sincere appreciation to my family and my mom for their unconditional support in my life. May God richly bless you. v TABLE OF CONTENTS Page DECLARATION AND COPYRIGHT........................................................................................... ii CERTIFICATION ......................................................................................................................... iii DEDICATION ............................................................................................................................... iv ACKNOWLEDGEMENTS ............................................................................................................ v LIST OF TABLES ........................................................................................................................ xii LIST OF FIGURES ...................................................................................................................... xv ABSTRACT .................................................................................................................................. xx CHAPTER 1 General Introduction ...................................................................................................................... 1 1.0 Climate change and insect phenology ................................................................................... 2 1.1 Insect Thermal Biology and Physiology ............................................................................... 3 1.2 Insect freeze strategies and supercooling points (SCPs) ....................................................... 9 1.3 Phenotypic plasticity in insects as a response to changes in temperature ........................... 11 1.4 Economic Importance of Cereal Stemborers ...................................................................... 12 1.4.1 Biology and Ecology of Busseola fusca ....................................................................... 13 1.4.2 Biology and Ecology of Sesamia calamistis ................................................................ 13 1.4.3 Biology and Ecology of Chilo partellus ....................................................................... 14 1.5 Control of Cereal Stemborers .............................................................................................. 15 1.5.1 Chemical Control .......................................................................................................... 15 1.5.2 Cultural Control ............................................................................................................ 16 1.5.3 Push - Pull Technology................................................................................................. 17 1.5.4 Biological control ......................................................................................................... 18 1.6 Biology and ecology of Cotesia flavipes and Cotesia sesamiae ......................................... 18 vi 1.7 Problem statement and justification of the study ................................................................ 19 1.8 Objectives ............................................................................................................................ 22 1.8.1 Overall Objective .......................................................................................................... 22 1.8.2 Specific Objectives ....................................................................................................... 23 1.8.3 Hypotheses.................................................................................................................... 23 References ................................................................................................................................. 23 CHAPTER 2 Dominance of spotted stemborer, Chilo partellus Swinhoe (Lepidoptera: Crambidae) over indigenous stemborer species in Africa’s changing climates: ecological and thermal biology perspectives ................................................................................................................................... 39 2.1 Introduction ......................................................................................................................... 40 2.2 Africa’s Changing Climate.................................................................................................. 45 2.3 Competitive Displacement of Indigenous Stemborer Species ............................................ 46 2.3.1 Extension of C. partellus geographical range .............................................................. 48 2.3.2 Increase in numbers of C. partellus generations .......................................................... 50 2.3.3 Overwintering of C. partellus ....................................................................................... 53 2.3.4 Impact of Variability in Temperature and Relative Humidity on the Ecology of Stemborers ............................................................................................................................. 55 2.3.5 Physiological Tolerances in C. partellus ..................................................................... 58 2.3.6 Host range of C. partellus ............................................................................................ 65 2.3.7 Asynchrony between C. partellus and its natural enemies ........................................... 66 2.4 Future Directions and Conclusions ..................................................................................... 67 References ................................................................................................................................. 70 CHAPTER 3 Comparative assessment of the thermal tolerance of spotted stemborer, Chilo partellus Swinhoe (Lepidoptera: Crambidae) and its larval parasitoid, Cotesia sesamiae Cameron (Hymenoptera: Braconidae)…… ........................................................................................................................... 81 3.1 Introduction ........................................................................................................................