The ecology and evolution of insect pathogens

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In order to be able to manage the environment effectively, either in terms of preserving biodiversity, protecting our crops from pests or maintaining human health, we need to understand how different organisms interact and what mechanism underlie the patterns we observe.  One of the key components of our environment is the pathogens that cause diseases of varying severity in virtually all groups of plants and animals.  This programme will focus on the interactions between an insect, the western tent caterpillar, and a virus pathogen.  Tent caterpillars are often seen on deciduous trees in early summer however, when their numbers are high they are frequently killed by a virus disease which attacks the caterpillar stage.  This disease is thought to play an important role in the population fluctuations that are so evident in this insect every 8-11 years.  In this programme we will study several tent caterpillar populations found in the vicinity of Vancouver, BC.  We are particularly interested in the evolution of this interaction: whether the resistance of the insect to the virus alters as it changes in density, and how the virus population responds to this in terms of its virulence.  We are not just interested in recording numbers: we also want to study the genetics of the interaction and the role that different levels of genetic variation play in the outcome.  Our earlier research has shown that the virus populations are highly variable genetically and that this is influenced by the spatial structure of the different populations.  One of the questions we want to answer is why is the virus population so variable?  We suspect that infections made up of many closely related virus strains are more pathogenic than any single strain.  However, we want to be able to test this idea in a natural population and to understand why it is that more viruses are better than one.  We also want to understand how infection by the virus affects the genetics of insect, for example, are there times in the population cycle when the insects are more susceptible and what is its basis? The findings from this project will have implications, not only for the role of pathogens in wildlife populations, but also in terms of understanding the development of disease severity in human diseases and pathogens of agricultural interest.