Sex-specific differences in nutrient regulation in a capital breeding caterpillar, Spodoptera litura (Fabricius)

Nutrient requirements by male and female insects are likely to differ, but relatively little is known regarding how sexes differ in their regulation of macronutrient acquisition. The present study reports the results from a laboratory experiment in which behavioural and physiological components of nutrient regulation were compared between male and female caterpillars of Spodoptera litura (Fabricius). When provided with choices between two nutritionally complementary foods (one is a protein-biased diet and the other a carbohydrate-biased diet), both males and females adjusted their food selection to defend an intake target. However, the composition of diet preferred by the two differed, with females selecting significantly more protein than males with no difference in carbohydrate intake between the two. When confined to single diets with varying mixtures of protein and carbohydrate [P:C ratios, expressed as the percentage of diet by dry mass: protein 42%:carbohydrate 0% (p42:c0), p35:c7, p28:c14, p21:c21, p14:c28, p7:c35], females consumed more macronutrients than did males across on all P:C diets except the extremely carbohydrate-biased diet (p7:c35). Under both choice and no-choice feeding condition, such sex differences in nutrient intake were not expressed until late in the feeding stage of the final stadium. Sexes also differed in post-ingestive utilization of ingested nutrients. Females utilized ingested protein for body growth with greater efficiency compared to males, presumably reflecting provisioning their adult needs for protein to develop eggs, whereas males were more efficient at depositing lipids from carbohydrate intake than females.

Research highlights▶ Male and female individuals may require different mixture and amount of multiple nutrients to maximize their respective reproductive output. However, less is known how the two sexes differ in their physiological and behavioural regulation of macronutrient input. The present study investigates sex-specific differences in macronutrient regulation in a capital breeding caterpillar of Spodoptera litura. Results show that female caterpillars consumed more protein than males, and were more efficient at converting protein intake to body protein growth than did males, reflecting their high protein investment for egg production. However, males regulated their body lipid storage to a greater level compared to females, which may be related to their greater propensity to migrate. The present study highlights how sex-specific differences in nutritional requirement for reproduction are controlled differently by each sex.