Thesis Title COMPENSATION BY POPULATIONS OF RODENT PESTS TO APPLIED CONTROL MEASURES IN INTENSIVE CROPPING SYSTEMS Peter R. Brown A thesis submitted for the degree of Doctor of Philosophy. School of Biological, Earth and Environmental Sciences, The University of New South Wales. Submitted September 2005. ii Certificate of Originality I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, nor material which to a substantial extent has been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where any due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged. (Signed) ………………………………………………… iii Acknowledgements I wish to express my sincere thanks to many people who have assisted me in this endeavour and for their support. I have received invaluable support from Penny and Kieran, and I am eternally grateful. I thank all my colleagues at CSIRO for their assistance with various aspects of this work: Tony Arthur, Lisa Chambers, Stephen Davis, Stephen Day, Micah Davies, David Grice, Lyn Hinds, Jens Jacob, Dean Jones, Alice Kenney, Charles Krebs, Katrina Leslie, Chris Margules, Steve Morton, Roger Pech, Bill Price, Tony Robinson, Grant Singleton and Monica van Wensveen. I am also grateful to Phil Dunbar, Neil Huth and Greg Mutze. I sincerely thank my friends and colleagues in Vietnam (Cảm ơn ông và bà, quá tử đối vối tôi), particularly Mr Tuan, Prof Tuat, Dr Tan, Mrs Hue, Mrs Hoa, Mrs Ha, Mr Kien, Ms Lien, Ms Yen, Mr Hoa (“HP”) and especially Mr Bia Hoi (“mốt, hai, ba, yo!”). I especially thank the hospitality of my farmer friends and families, particularly Mr Coi (and Mrs Coi and Ms Lien), Mr Hung (“it’s raining”), Mr Dung, Mr Thanh, Mr Que, Mr Hung and Mr Manh, and no thanks would be too much for Mr Grabbit. I also thank the following Australian farming families for allowing me to trap mice on their farms: Blacks, Hannigs, Crothers, Hastings, Lesters, Meads, Poles, Saals, Thompsons, Walters, Wilsomores and Ziesemers. Finally, my sincere thanks go to Grant Singleton and Peter Banks. They have challenged me, and I have benefited greatly and enjoyed their intellectual stimulation and discussions. I acknowledge the support provided to me from CSIRO Sustainable Ecosystems, the Australian Centre for International Agricultural Research (ACIAR), and the University of New South Wales. This Thesis was conducted in compliance with the regulations of the CSIRO Sustainable Ecosystems Animal Ethics Committee (01/02 – 15). iv Summary Rodents cause significant damage to crops throughout the world including damage to wheat by feral house mice (Mus domesticus) in southeastern Australia and damage to rice crops by ricefield rats (Rattus argentiventer) in Southeast Asia. Much time and effort goes into controlling these pests, but control is generally applied after damage has already occurred and there is little understanding of how rodent control affects crop yields. This research was designed to understand how rodent populations recover after control, how crops compensate for damage, and to determine the relationship between rodent abundance and yield loss. These findings will lead to better management of rodents through appropriate timing of control, to minimise damage or yield loss of crops and result in better benefit:cost ratios for farmers. Replicated, manipulative, field studies were conducted in Vietnam and Australia. For ricefield rats in Vietnam, after population control had been applied, population abundance on treated sites was lower during summer, but was higher during winter compared to untreated sites. Furthermore, there was an increase in the proportion of juveniles and a decrease in the body weight of animals. The ricefield rats had variable but large home range sizes, allowing for rapid population recovery after control. For house mice in Australia, densities were lower on treated sites after control, there was a bias towards females and a decrease in survival compared to untreated sites. Poor survival was the only demographic characteristic that was exhibited both for rodenticide-induced population crashes and natural population crashes that occur at the end of mouse plagues. Wheat crops compensated when <50% of tillers were damaged early in the growth of the crop, however, when damage occurred later yield loss was proportional to the level of damage imposed. Compensation was through an increased number of tillers produced and through better survival of tillers. A sigmoidal relationship was found between the density of mice and damage to wheat. Most damage occurred at emergence of the crop when densities were >100 mice/ha. These results from Australia and Vietnam highlight the need to conduct rodent management before sowing or before breeding commences, over large areas, and to focus on key refuge and breeding habitats. This will reduce reinvasion and maximise the effect of any control applied. v COMPENSATION BY POPULATIONS OF RODENT PESTS TO APPLIED CONTROL MEASURES IN INTENSIVE CROPPING SYSTEMS Peter R. Brown CSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT, 2601, Australia School of Biological, Earth and Environmental Sciences, The University of New South Wales, NSW, 2052, Australia This thesis is based on the following publications and manuscripts that are referred to in the text by their Roman numerals: I. Brown, P. R., Tuan, N. P., and Banks, P. B. (In Press). Movements, habitat use and response of ricefield rats to removal in an intensive cropping system in Vietnam. Belgian Journal of Zoology. II. Brown, P. R. and Tuan, N. P. (In Press). Compensation of rodent pests after removal: control of two rat species in an irrigated farming system in the Red River Delta, Vietnam. Acta Oecologica. III. Brown, P. R. (Manuscript). Short- and long-term demographic changes in house mouse populations after control in dryland farming systems in Australia. Manuscript. IV. Brown, P. R. (2005). The effect of simulated house mouse damage to wheat in Australia. Crop Protection 24, 101-109. V. Brown, P. R., Huth, N. I., Banks, P. B., and Singleton, G. R. (Manuscript). Relationship between abundance of pest rodents and damage to agricultural crops. Manuscript. vi Table of Contents Thesis Title........................................................................................................................i Certificate of Originality ................................................................................................ii Acknowledgements.........................................................................................................iii Summary.........................................................................................................................iv Table of Contents ...........................................................................................................vi List of Tables ...................................................................................................................x List of Figures...............................................................................................................xiii Chapter 1. Introduction.................................................................................................1 1.1 Worldwide impact of rodent pests.....................................................................1 1.2 Rodents in SE Asia............................................................................................4 1.3 House mice in Australia ....................................................................................8 1.4 Impact on crops ...............................................................................................11 1.5 Response of rodent populations to control or removal....................................13 Key Question 1: How do rodent populations recover from control?......................14 1.6 Compensation by crops to damage by rodents................................................16 Key Question 2: How do wheat crops compensate for rodent damage? ................18 1.7 The relationship between rodent abundance and crop damage.......................19 Key Question 3: What is the relationship between rodent abundance and crop damage or yield loss?...............................................................................................20 Chapter 2. Study areas and species ............................................................................22 2.1 The ricefield rat in Southeast Asia ..................................................................22 2.2 House mice in Australia ..................................................................................29 Chapter 3. Results and Discussion..............................................................................35 3.1 How do rodent populations recover from control?..........................................35 3.1.1 Movements................................................................................................35 3.1.2 Demographic responses ............................................................................36