EFFECTS OF THERMAL STRESS ON THE BROWN PLANTHOPPER NILAPARVATA LUGENS (STAL) by JIRANAN PIYAPHONGKUL A thesis submitted to the University of Birmingham For the degree of DOCTOR OF PHILOSOPHY School of Biosciences University of Birmingham February 2013 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract This study investigated the effects of heat stress on the survival, mobility, acclimation ability, development, reproduction and feeding behaviour of the brown planthopper Nilaparvata lugens. The critical information derived from the heat tolerance studies indicate that some first instar nymphs become immobilized by heat stress at around 30°C and among the more heat tolerant adult stage, no insects were capable of coordinated movement at 38°C. There was no recovery after entry into heat coma, at temperatures around 38°C for nymphs and 42-43°C for adults. At 41.8° and 42.5oC respectively, approximately 50% of nymphs and adults are killed. In a comparison of the acclimation responses between nymphs and adults reared at 23°C and acclimated at either 15 or 30°C, the data indicate that increases in cold tolerance were greater than heat tolerance, and that acclimation over a generation compared with a single life stage increases tolerance across the thermal spectrum. The temperatures that kill around 50% of nymphs and adults also exert negative effects on development and longevity. The same exposures also lower fecundity and extend egg development time through a combination of mating groups, in which the greatest effects occur when both males and females have experienced sub-lethal heat stress. Likewise, exposure to their ULT50 reduced feeding activity in both life stages of N. lugens. The amount of honeydew excreted by females and males in the treated nymph and adult groups were 3-4x and 2-3x lower than in the equivalent control groups. Overall, sub-lethal heat stress extended egg development time, inhibited nymphal development, lowered fecundity and reduced feeding activity. i This thesis is dedicated to my deceased parents “Whatever the mind can conceive and believe it can achieve.” Napolean Hill quote Quoted in ‘Coming from Liberia’ by Ezike II, E.C. (2008) ii Preface This thesis is submitted for the degree of Doctoral of Philosophy at the University of Birmingham. All experiments were under the supervision of Professor Jeff Bale and carried out in the School of Biosciences from June 2009 to June 2012. This research is totally original and contains nothing that is the outcome of collaboration except where appropriately referenced. No part of this thesis has been submitted for any other degree, diploma or any other qualification. It does not exceed 50,000 words in length. Parts of this thesis have been published in: Piyaphongkul J., Pritchard J. and Bale J.S. (2012) Can tropical insects stand the heat? A case study with the brown planthopper Nilaparvata lugens (Stål). PLoS ONE, 7 (1): e29409 Piyaphongkul J., Pritchard J. and Bale J.S (2012) Heat stress impedes development and lowers fecundity of the brown planthopper Nilaparvata lugens. PLoS ONE, 7 (10): e47413 Other sections of the thesis are being prepared for publication as follows: Piyaphongkul J., Pritchard J. and Bale J.S. Effects of acclimation on the thermal tolerance of the brown planthopper Nilaparvata lugens (Stål). Piyaphongkul J., Pritchard J. and Bale J.S. Influence of short exposure to high temperatures on feeding activity of the brown plant hopper Nilaparvata lugens (Stål). iii Piyaphongkul J., Johnson B., Coleman P., Hands S., Pritchard J. and Bale J.S. Relationship between body size and dynamics of thermal equilibrium in insects. Piyaphongkul J., Pritchard J. and Bale J.S. Temperature calibration of system used to measure insect activity thresholds. Jiranan Piyaphongkul February 2013 iv Acknowledgements First and foremost, I would like to offer my utmost gratitude to my superb supervisor, Prof. Jeff Bale, who has continuously supported me throughout my dissertation. He has patiently helped editing my dissertation and provided advice, encouragement and research vision that is very important for me as I wish to become good doctoral researcher. My dissertation would not be complete without him. Besides my supervisor, I would like to thank my co-supervisor, Dr. Jeremy Pritchard who has offered much advice and insight throughout my research. My sincere thanks also go to Dr. Scott Hayward for assistance with some techniques and for providing comments on my work. I would like to thank Prof.Brian Ford-Lloyd and Prof.Simon Leather for providing many valuable comments that improved the contents of this dissertation. I am also very grateful to Dr. Mohamad Bahagia AB Ghaffar (known as ‘Mr. Happy’) for his advice on the culture of rice and insects and general laboratory techniques. I would like to thank all members of staff at the School of Biosciences for their friendly assistance and good support. I would like to thank my colleagues in insect eco-physiology lab group: Lucy, Gwen, Stuart, Bobbie, Megan, Paul, Emily, Matt and Nicky for their assistance, encouragement and friendship. Thanks to all of you for creating of such wonderful social and outdoor activities. I am grateful to Miss Jutharat Voraprateep, a PhD student in the School of Mathematics for guidance on statistical analysis. Thanks also to Dr. Jedsada Manyam, Dr Athikhom Manoi and Dr. Chinnapat Panwisawas who offered advice on the work on thermodynamics. I am also v thankful to my best friends, Miss Patcharawarin Ruanto, Dr. Chinnapat Panwisawas, Miss Wilai Siriwatcharapiboon and Vanesse Wong, who shared my happiness and sadness. I am lucky to have the support from many good Thai friends in Birmingham: Komson, Suwijak, Cherry, Eakasit, Suchada and others. My sincere thanks also go to my former project advisor, Associate Professor Dr.Pornsilp Pholpunthin at the Biology Department, Prince of Songkhla University and Associate Professor Dr.Nantana Gajaseni at Chulalongkorn University, who provided a role model for the type of lecturer and scientist I wish to be. I am grateful to Dr. Tang-on Prommi and other all members of staff at the Faculty of Liberal Art and Sciences, Kasetsart University for their help, encouragement and support and communication of all important documents during my period of study in Birmingham. I would like to thank Royal Thai Government, Development and Promotion of Science and Technology Talents project (DPST) and the Office of Educational Affairs (OEA) at the Royal Thai Embassy, London, not only for providing me with the government scholarship, but also for giving me the opportunity to attend the conferences and establish good research connections for my future career. Special thanks to my dearest husband, Kang, who has always stood by me and patiently waited me with constant love. I would like also to thank my brothers and sisters for their encouragement and support. Finally, I would like to express my extreme gratitude to my deceased parents for their love and support. I would like to apologise to anyone who has helped me and I have not mentioned here. vi Table of contents List of Figures …………………………………………………………………………………...xiii List of Tables……………………………………………………………………………..……...xix Chapter 1 General introduction…………………………………………………………………1 1.1 Climate change…………………………………………………………………………….3 1.2 Impacts of climate change on insects………………………………………………….......9 1.3 Thermal biology and insect physiology…………………………………………………..11 1.3.1 Background…………………………………………………………………………12 1.3.2 Thermoregulation in insects………………………………………………………..14 1.3.3 Temperature tolerance……………………………………………………………...19 1.4 Ecology and biology of the brown planthopper, Nilaparvata lugens……………………..22 1.4.1 Development and life cycle……………………………………………………..….23 1.4.2 Feeding behaviour………………………………………………………………….24 1.4.3 Migratory behaviour and distribution………………………………………………25 1.4.4 Outbreaks and economic impacts…………………………………………..………28 1.5 Objectives………………………………………………………………………..………..29 vii Chapter 2 Temperature calibration of system used to measure insect activity thresholds...30 2.1 Abstract…………………………………………………………………………...……….30 2.2 Introduction………………………………………………………………………………..31 2.3 Material and methods…………………………………………………………………...…33 2.4 Results……………………………………………………………………………………..36 2.5 Discussion and conclusions…………………………………………………………...…..41 Chapter 3 Relationship between body size and dynamics of thermal equilibrium in insects………………………………………………………………………………………… 45 3.1 Abstract…………………………………………………………………………...……….45 3.2 Introduction………………………………………………………………………………..46 3.3 Material and methods…………………………………………………………………...…49 3.3.1 Insect materials……………………………………………………………………..49 3.3.2 Measurement of surface-to-volume ratio…………………………………………..50 3.3.3 Measurement of Tb and time required to reach thermal equilibrium…………….....50 viii 3.4 Results……………………………………………………………………………………..53 3.4.1 Surface-to-volume ratios………………………………………………….………..53 3.4.2 Effect of body size on lag times…………………………………………..………..54