Life stage- and sex-specific sensitivity to nutritional stress in a holometabolous insect

Over the course of their lives, organisms can be repeatedly exposed to stress, which shapes their phenotype. At certain life stages, known as sensitive phases, individuals might be more receptive to such stress than at others. One of these stresses is nutritional stress, such as food limitation. However, little is known about how plastic responses differ between individuals experiencing nutritional stress early versus later in life or repeatedly, particularly in species with distinct ontogenetic niches. Moreover, there may be sex-specific differences due to distinct physiology. The turnip sawfly, Athalia rosae (Hymenoptera: Tenthredinidae), is a holometabolous herbivore, whose larvae consume leaves and flowers, while the adults take up nectar. We examined the effects of starvation experienced at different life stages on life-history traits as well as adult behavioural and metabolic traits to determine which life-stage may be more sensitive to nutritional stress and how specific these traits respond. We exposed individuals to four distinct nutritional regimes, no, larval, or adult starvation, or starvation periods during both larval and adult stage. Larvae exposed to starvation had a prolonged developmental time, and starved females reached a lower initial adult body mass than non-starved individuals. However, males did not differ in initial adult body mass regardless of larval starvation, suggesting the ability to conform well to poor nutritional conditions, possibly through changes in development and metabolism. Adult behaviour, measured as activity, was not significantly impacted by larval or adult starvation in either sex. Individuals starved as larvae had similar carbohydrate and lipid (i.e. fatty acid) contents as non-starved individuals, potentially due to building up energy reserves during their prolonged development, while starvation during adulthood or at both stages led to reduced energy reserves in males. This study indicates that the sensitivity of a life stage to nutritional stress depends on the specific trait under consideration. Life-history traits were mainly affected by larval nutritional stress, while activity appeared to be more robust and metabolism mostly impacted by the adult nutritional conditions. Individuals differed in their ability to conform to the given environment, with the responses being life stage- and sex-specific.