Investigating the Mechanisms Behind Moth Declines: Plants, Land-use and Climate Dan Blumgart August 2020 A thesis submitted to Lancaster University in fulfilment of the requirements for the degree of Doctor of Philosophy Project supervisors James Bell Rothamsted Insect Survey, Rothamsted Research Rosa Menendez Lancaster Environment Centre, Lancaster University Marc Botham Centre for Ecology and Hydrology 1 Declaration and funding statement I declare that the work presented in this thesis is my own and has not been submitted elsewhere for the award of a degree of Doctor of Philosophy. The illustrations at the beginning of each chapter are also my own work. This work was funded by the Natural Environment Research Council (NERC) through the Envision Doctoral Training Program awarded to Lancaster University and Rothamsted Research. Dan Blumgart 22nd August 2020 ii Acknowledgements Thanks go firstly to James Bell, Rosa Menendez and Marc Botham, my three supervisors. Thanks to James, for his encouragement and enthusiasm, and all the hours spent with me going through my work. Thank to Rosa for being so quick and thorough with corrections and feedback, and thanks to Marc for pushing me to think more deeply about the ways of moths. Thanks to everyone in the Rothamsted Insect Survey team, especially to Chris Shortall for answering my endless questions about the database and to Mike Hall for all the woodwork he did for me, as well as all the advice on everything DIY-related. Thanks to Butterfly Conservation for support and to the Centre for Ecology and Hydrology for hosting me several times and arranging my stay at Hillesden Farm. Also, thanks to the Ecological Community Trust for funding the purchase of the grass and wildflower seed used in my field trials. Thanks to Paul Compton for his help with designing and making 25 LED battery-powered moth-traps. I don’t know what I would’ve done without his electronics knowledge. Thanks to Todd Jenkins and Alex Dye for their loyal assistance with the night-time fieldwork. There aren’t many people who would enjoy, or even tolerate, wandering along the edges of fields catching moths deep into the night. Despite the fatigue, I enjoyed our deep chats and the excitement of finding something that wasn’t yet another Agriphilla straminella! Thanks also to my temporary field assistants Dion, Kelly, Meg, Sarah, Cait and Mum. Thanks especially to Mum – I have never seen anyone so excited about catching a moth in a net. Thanks to the farm team, especially Chris Mackay, for sowing and maintaining my field margins. Thanks to Jamie Orpwood who let me camp out at Hillesden Farm during fieldwork in my first field season. Thanks to Suzanne Clark for all the statistics consultations and for helping me design the randomised blocked field trial. Thanks also to Kirsty Hassall for help with my idiosyncratic stats problems. Thanks to Donna Fellowes for her flawless running of the postgrad system at Rothamsted. Thanks to Colin Harrower for teaching me how to up my game in R and saving me countless hours of labour by showing me how to write loops. Thank you to all the volunteers of the RIS light-trap network, with special thanks to Paul Verrier for maintaining the database. Without all of you, my project could never have existed. Thanks to Colin Plant for teaching me how to dissect moths and mount their genitals. Also thank you to my housemates, Matt and Cassie, for tolerating my constant occupation of the kitchen table iii while I dissected my endless quantities of moth genitals. Thanks again to Mum for her proofreading services. Thanks to my friend, colleague, and PhD predecessor Aislinn Pearson for her bountiful advice about everything PhD-related. If it weren’t for her, I’d still be using R and Word like an amateur. Finally, thanks to my family: Mum, Dad, Julie, and Cait, for supporting me in my decision to become a doctor of moths. iv Abstract Moth populations have declined across large areas of north-western Europe since the mid- 20th century, mirroring similar declines in other insect groups. The mechanisms behind these declines are likely manifold, but it is believed that agricultural intensification is a key factor. There were two aims of this thesis: (1) to elucidate the mechanisms behind moth decline in the UK, and (2) to determine ways in which farmland habitats could be improved for moths. Counter to expectations, between 1968 and 2016, the declines in total moth abundance were least severe in the most agriculturally intensive areas and were most severe in semi-natural habitats, as well as in urban environments. Species richness, while remaining stable at the national level, declined in only one habitat type: broadleaf woodland. No evidence was found to support the hypotheses that habitat loss, shading of the understory by canopy-closure, or overgrazing by deer had driven these declines within broadleaf woodland. Evidence was found that warm winters negatively impacted moth abundance, but this effect was consistent across all habitats. Although declines were least severe in improved grassland and arable land, the declines in total abundance were significant and ongoing, despite widespread and increasing adoption of agri-environment schemes (AES) since the early 1990s. In this thesis, the role of nectar resources and larval hostplants were explored within AES field margins on arable land, with the aim of determining how these small areas of habitat could be best managed to enhance moth abundance and diversity. It was found that the diversity of moths was greatly increased, and abundance moderately so, when margins were sown with a wide range of wildflowers and grasses, in comparison to only grasses. The evidence suggested that this was due primarily to the provision of larval hostplants, with nectar resources playing a secondary role. Overall, this thesis demonstrates that, in order to improve the environment for moths, AES wildflower margins should be encouraged over and above plain grass margins. This thesis also demonstrates that while agricultural intensification is likely responsible for some of the observed declines in moths, there are other mechanisms, as yet unknown, at work in both semi-natural habitats and urban areas. v Contents Declaration and funding statement ......................................................................................... ii Acknowledgements ................................................................................................................. iii Abstract .................................................................................................................................... v List of acronyms used ............................................................................................................. xii List of figures ......................................................................................................................... xiv List of tables ......................................................................................................................... xvii Chapter 1. Introduction and literature review ........................................................................ 2 1.1 Overview of insect declines ........................................................................................... 4 1.1.1 Insect declines in the UK ......................................................................................... 4 1.1.2 Global insect declines ............................................................................................. 5 1.2 Evidence for moth population decline ........................................................................... 7 1.2.1 UK trends ................................................................................................................ 7 1.2.2 European trends ..................................................................................................... 8 1.3 Drivers of moth population change ............................................................................. 10 1.3.1 Habitat loss ........................................................................................................... 11 1.3.2 Direct and indirect effects of agrochemicals ......................................................... 18 1.3.3 Light pollution ....................................................................................................... 20 1.3.4 Climate change ..................................................................................................... 21 1.3.5 Non-native species ................................................................................................ 22 1.4 Conservation measures ............................................................................................... 22 1.4.1 Field margin creation ............................................................................................ 23 1.4.2 Reduction in chemical input .................................................................................. 27 1.4.3 Reduction in grazing intensity ............................................................................... 28 1.4.4 Hedgerow management ....................................................................................... 28 1.5 Research objectives and thesis structure .................................................................... 29 vi 1.5.1 Chapter 2 – The effect of land-use and species traits on the long-term trends of abundance and diversity of moths in the UK ................................................................