This thesis looks at the immunology of Australian locusts in a broad ecological context. By investigating some of the ecological parameters commonly known to influence locusts, this work ties many of the underlying immune-based mechanisms of locusts, ultimately providing insight into the success of these animals in the field. In the context of locust biocontrol strategies, this is particularly important. In Chapter 2, the density-dependent prophylaxis hypothesis was tested in Chortoicetes terminifera; a theory predicting that group-living animals invest more in immune function compared to solitarious conspecifics. Through the use of several conventional immune assays, C. terminifera was found to both support and oppose the theory, accounting for the contradictory literature currently existing on this topic. The effect of cannibalism on disease transmission was investigated in Chapter 3. Starved locusts were found to significantly cannibalise uninfected over fungal-infected victims. Without an alternative food source, locusts succumbed to starvation rather than consume infected victims, revealing a striking adaptation of infection avoidance. Chapter 4 investigated predictive immune response in C. terminifera. After measuring several immune parameters in locusts exposed to live or dead infected conspecifics, physiological immune anticipation was not detected. In Chapter 5, gene expression assays were developed in Locusta migratoria to investigate immune gene expression variation across different tissues and immune states. These assays found distinct tissue-specificity across genes, highlighting the importance of tissue selection in such assays. Gene expression assays were applied in Chapter 6 to investigate variation in locust immunity in response to bacterial introduction to the gut. Results suggested that alteration of microbiota communities could induce subtle immune responses within hosts, supporting the need for further study in this field
