The interaction between migration and disease in the Fall Armyworm,
      'Spodoptera frugiperda'
Creators: name: Pearson, Aislinn
Publisher: name: Lancaster University
Year: 2016
Subjects: Insect migration
Fall armyworm
Spodoptera frugiperda
baculovirus
sfMNPV
Flight mill
Bateman's principle

description: Every year billions of insects undertake long-distance seasonal
      migrations, moving hundreds of tonnes of biomass across the globe and
      providing key ecological services. Yet we know very little about the
      complex migratory movements of these tiny animal migrants and less still
      about what causes their populations to fluctuate in space and time.
      Understanding the reason for these population level changes is important,
      especially for insect species that are agricultural pests and disease
      vectors. One possible driver of large scale population dynamics in
      migratory insect species is disease. Migration is a stressful and
      energetically-costly behaviour. Fighting off, or living with, infections
      is also costly. In migratory animals that have been exposed to disease
      this may lead to potential trade-offs between investment in migration and
      investment in the resistance and tolerance mechanisms associated with
      infection. Using a combination of rotational flight mills, bioassays and
      molecular techniques, this thesis uses the fall armyworm, Spodoptera
      frugiperda, and its associated baculovirus, S. frugiperda multiple
      nucleopolyhedrovirus (SfMNPV), as a model system to describe the trade-off
      between migratory effort and disease susceptibility, and how this affects
      disease dynamics at a geographic scale. After a general introduction to
      the topic (Chapter 1), Chapter 2 uses an inter-species analysis to
      describe the insect flight patterns associated with migratory behaviour in
      three species of migratory noctuid moth, linking these with previous work
      on the upregulation of genes associated with the migratory syndrome and
      providing evidence of sex-biased dispersal in the fall armyworm. Chapter 3
      builds on these results by quantifying the impact of infection on
      migratory flight behaviour, and provides the first evidence of Bateman’s
      principle in insect migrants by demonstrating that males and females
      exhibit different developmental and physiological responses to infection,
      and adopt different flight strategies following virus exposure. To
      understand how this affects susceptibility, Chapter 4 quantifies the
      effect of flight effort on resistance to infection, showing that prolonged
      bouts of flight results in an increase in disease loads but only in
      populations with low levels of background infection. This provides
      evidence that the trade-off between flight effort and resistance is
      context dependent and possibly phenotypically plastic. Finally, Chapter 5
      contextualises these laboratory results by investigating fluctuations in
      disease load across the United States of America. Findings from this study
      show that the host-pathogen system is relatively stable over large
      geographic distances and time periods of up to two years. Where variation
      does occur, there is evidence for ‘escape’ from infection but that this is
      often associated with the cost of reduced resource availability in males.
      Overall the work demonstrates key physiological and behavioural
      adaptations that enable insects to engage in long-distance migration when
      faced with competing costs of flight and disease resistance.