Abstract/Summary

Intraspecific variation is the variation found among individuals of a species and has historically been ignored by ecologists. However, studies are beginning to reveal the importance of intraspecific variation on the ecological performance of individuals and populations; populations have been found to be less vulnerable to environmental change and have more stable sizes when the individuals that composed them are more diverse. Although intraspecific variation is being increasingly explored in ecology, the majority of research has been done using ecological models and observations and have primarily focused on terrestrial vascular plants and freshwater fish. This leaves a gap on experimental research on invertebrate species. Pest and invasive species, including many invertebrates, are a global problem affecting both the economy and natural ecosystems. Knowledge gaps in the intraspecific variation literature present the opportunity to explore the importance of intraspecific variation in an applied way; to see whether it can be used to help manage and improve pest and biological control species. This thesis therefore aimed to improve our understanding of how intraspecific variation influences population and individual process: (1) within insect species, (2) using controlled experimental studies, and (3) under varying environmental conditions. Each chapter focuses on a different pest or biological control model system to provide guidance for improved pest and invasive species management. Chapter 1 aimed to investigate the effects of intraspecific variation on the pest species, Sitophilus oryzae, under novel and heterogeneous environments. Chapter 2 explored whether intraspecific variation could improve the biological control performance of Aphalara itadori in the UK, and whether its performance would differ under present and future environmental conditions. Finally, Chapter 3 tested the effects of intraspecific variation on multiple trophic levels using the polymorphic pest species, Callosobruchus maculatus, its potential biological control Dinarmus basalis. All experimentation was undertaken at the University of Reading Campus and CABI, UK. Our studies revealed the intraspecific phenotypic and/or genetic variation were not always important for the performance and dynamics of pests and biological controls species under constant or different environmental conditions. Instead, effects varied across experiments and model systems. For example, phenotypic variation did not affect the overall performance of the pest species S. oryzae on the four different grain treatments tested. However, it did affect offspring performance of the polymorphic pest species, C. maculatus, with offspring survival varying by morph variant in the presence of its biological control. In terms of genetic variation, the hybrid S. oryzae population showed some improved performance (although not for all responses considered), whilst hybrid populations of A. itadori were less efficient under both environmental conditions tested. This variation in the importance and consequences of intraspecific differences on the performance of invertebrate species means that we cannot safely conclude that variation is always good, or bad, or irrelevant. Therefore, as a cautionary approach we would recommend ecologists and managers to explicitly consider intraspecific variation within their studies and applied work.