Feeding ecology of outbreak insect species

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Results from field and laboratory rearing experiments indicate that total tannin fraction of balsam fir tree foliage appears to serve as mechanisms of host resistance to spruce budworm. However, the specific tannins involved and their individual mode of action remain to be investigated. I hypothesize that specific foliar tannins act synergically to influence larval survival and growth by interfering with larval food utilization processes and that these specific tannins have different modes of action on budworm larvae. This hypothesis will be tested using gravimetric, behavioral, electrophysiological, and histological studies on larvae reared on artificial diet supplemented with various levels and combinations of pure chemicals extracted from foliage. According to the local-adaptation hypothesis, the spatial heterogeneity in nutritive, defensive, or phenological traits within populations of long-lived plants structures populations of short-lived, specialized herbivores into demes (genetically different populations) adapted to the phenotypes of individual hosts. I hypothesize that food quality deterioration (change in host phenotype caused by successive insect defoliation) during an outbreak exerts a selective pressure on budworm population that changes gene frequency of the population which in turn leads to a better adaptation to poor feeding conditions. Reciprocal transfert experiments will be conducted over four successive generations of insect under laboratory conditions using postdiapausing siblings and fresh foliage from damaged stands or foliage from undamaged stands. Spruce budworm biological performances will be documented and quantitative genetic analysis performed. Additional laboratory rearing experiments will be conducted using high and low quality diets to investigate the processes involved in the impact of nutritional stress on spruce budworm over several generations. I hypothesize that, through selective pressure, nutritional stress imposed on spruce budworms over several generations modifies larval development and food utilization, optimal nutrient balance and responses to positive and negative food quality changes (nutrient and secondary compounds).