The nutritional and behavioural ecology of Doratifera casta and Mnesampela
privata
B.Sc. (Hons) 1999
Insect-plant dynamics are influenced by multiple trophic levels and spatial and temporal variation in plant quality and insect feeding. Eucalpyts in Australia are characterised by relatively high levels of herbivory. Both Doratifera casta and Mnesampela privata are lepidopteran herbivores commonly found on eucalypts. Newly hatched larvae of both species tend to cluster together and skeletonise the surface of leaves. Later instar larvae feed alone and consume entire leaves. Different leaf properties and maintaining group structure are predicted to vary in importance to larval success at different life history stages owing to this shift in feeding behaviour. Using a series of field and laboratory experiments, I investigated hypotheses relating to the influence of leaf nutritional quality on foraging behaviour and how the interrelationship between ontogenetic changes in feeding by larvae may be reflected in both host use and morphology. Behaviour and the consumption of different diets influenced the survival of D. casta but not M. privata. Leaf structure and foraging position on a leaf are important factors influencing foraging behaviour of D. casta. I found that for early instar D. casta larvae it is essential to be in a group, kin or not, in order to successfully forage. Small M. privata larvae required a minimum group size in order to successfully complete a leaf roll which is used for shelter against both predation and desiccation. The ability and time taken to complete a leaf roll is influenced by group size, the structural properties of the leaves and the development stage of larvae. I found that nutritional and structural characteristics of host plants may influence the success of gregarious larvae. My results indicate that host choice for oviposition is important for relatively immobile early instar larvae. Factors that influence the potential success of gregarious larvae include the presence of conspecifics, the structural and chemical characteristics of host plants and the presence of predators and parasitoids. I also found the importance of these factors to the success of larvae varies ontogenetically and that these changes in foraging behaviour with development were related to group size changes. My studies indicate that there are clear interrelationships between nutrition, behaviour and morphology and that these should not be studied in isolation of each other and rather that they must be considered as interactive forces potentially influencing larval distribution and abundance.