Phenotypic variation in food utilization in an outbreak insect herbivore

The effects of nutrition may have subtantial impact on insect evolution by shaping different components of phenotypes. The key to undestanding this evolutionary process is to know how nutritional condition affects additive and nonadditive components of the phenotype. However, this is poorly understood in outbreaking insects. We investigated the additive and nonadditive variation present in food utilization traits in spruce budworm individuals subjected to chronic nutritional stress. A total of 160 full-sib families of spruce budworm (Choristoneura fumiferana Clem.) were raised under laboratory conditions, feeding on 2 diets (high and low energy) during 3 generations. Variables tested were pupal mass, consumption rate (RCR), growth rate (RGR), approximate digestibility (AD), the efficiency of conversion of digested food (ECD) and the efficiency of conversion of ingested food (ECI). Our results show that all traits tested presented a high percentage of nonadditive effects that modulate phenotype expression. We found a significant impact of family × diet interaction on pupal mass, RGR and ECD. Furthermore, these traits exhibited the greatest heritability. There was no evidence of presence of maternal effects. The results revealed that food utilization traits may evolve through epigenetics effects, such as phenotypic plasticity. This information can be used by modellers to improve forecast of spruce budworm population dynamics.