Lifetime consequences associated with varying macronutrient levels over a single generation for Heliothis virescens

Ratios of protein and digestible carbohydrate comprising an insect herbivore’s diet may have pronounced consequences on an individual’s performance and lifetime fitness. To date, though, most nutritional studies focus only on a single developmental stage. To investigate how macronutrient profile affects an insect herbivore’s lifetime performance, including reproductive ability, individual tobacco budworm larvae, Heliothis virescens, were reared from the neonate stage on one of seven different diets that differed in their protein (p) to digestible carbohydrate (c) ratios. Survival through eclosion peaked on diets with balanced or slightly protein-biased p:c ratios, with dietary imbalances having a greater effect on eclosion success for males compared to females. Developmental time was fastest on slightly protein-biased foods, but slowed considerably as the ratio of macronutrients became progressively more unbalanced. Pupal mass was highest on the slightly protein-biased food, but generally was not affected by macronutrient profile. Lipid content as a percentage of dry mass decreased linearly as the p:c ratio of the diet increased. Reproduction, which has rarely been examined in studies comparing protein and carbohydrate ratios, was significantly affected by diet macronutrient content. Egg production and viability were highest on foods with a balanced to slightly protein-bias, and non-existent on diets with low p:c ratios. The results from this experiment suggest that optimal intake targets observed in short-term studies correlate well with optimal lifetime performance in long-term studies. However, long-term studies, in contrast to short-tem studies, reveal that male survival and female fitness rates are highly sensitive to even slight macronutrient imbalances.