The Evolutionary Ecology of Antiviral Resistance in Insects

Infectious disease is ubiquitous and potentially devastating to individual hosts and populations as a whole. Understanding host resistance is therefore a key challenge. More specifically, understanding insect-virus interactions is crucial due to the role of insects as vectors of harmful human viruses, the potential role of insect viruses in the biological control of insect pest species and the impact which viruses have on beneficial insects such as the honey bee. Despite its importance, our understanding of resistance against viruses in insects and other invertebrates is less comprehensive than our understanding of resistance to bacterial and fungal parasites. In this thesis I investigate the resistance of the Lepidopteron host Plodia interpunctella to its natural viral parasite P. interpunctella Granulosis Virus (PiGV). I focus on two forms of antiviral resistance: (a) upregulation of an individual host’s (or their offspring’s) defences following previous exposure to a parasite, referred to as ‘immune priming’ and (b) host resistance following long term selection pressure from a parasite, referred to as ‘evolved resistance’. I examine these forms of resistance from an evolutionary and ecological perspective focusing on their associated costs and specificity. I find evidence for immune priming to virus for the first time in an insect but highlight that this form of resistance may carry costs and be context dependent in P. interpunctella. Using a mathematical modelling approach I also show that immune priming is likely to destabilise host populations. In addition, I show that antiviral resistance in P. interpunctella resulting from long term selection pressure with PiGV is non specific and localised in the gut. Furthermore, I find that resistance may be traded-off with developmental traits but that the detection of these trade-offs is dependent on the food quality on which P. interpunctella are raised.