Strategies used by female larval Lepidoptera to accumulate nutrient reserves

Abstract

Female insects produce eggs that are nutrient-rich. For most Lepidoptera, protein is acquired during larval feeding. Insects use pre-ingestive, post-ingestive and developmental strategies to meet nutritional needs. In this dissertation I examine the importance of these strategies to females of two related lepidopteran species differing in their adult feeding. Adult Heliothis virescens (Family Noctuidae) ingests nectar. The sexes were not distinguished according to their selective feeding behavior, but females accumulated more protein and carbohydrate. When restricted to diets, females ate and accumulated more protein on high protein diets. There were no sexual differences on high carbohydrate diets. Results indicate that female H. virescens larvae accumulate protein by regulating both intake and post-ingestive processing on high protein foods. Adult Estigmene acrea (Family Arctiidae) do not feed. The sexes did not differ in their selective feeding behavior. When restricted to diets, female E. acrea increased ingestion of diets unbalanced in protein and carbohydrate leading to greater intake of both nutrients but only accumulated more protein. Lastly, E. acrea prolong juvenile development if too small at later stages effectively extending their period of ingestion and processing. As previously shown protein-derived growth in female H. virescens progressively increased as dietary protein levels increased. Storage protein, a component of protein-derived growth, was found to similarly increase but was more abundant in females across all pupal stages and diets. Pharate adults retained a portion of total storage protein with females retaining greater levels presumably toward egg provisioning. Growth of both H. virescens and E. acrea was highly clustered compared to ingestion values suggesting post-ingestive processing of nutrients to regulate growth. Males and females of both species efficiently utilized carbohydrate except at high ingestion. Females of both species utilized nitrogen more efficiently than did males at all ingestion levels, contributing to their greater protein accumulation. The manner of post-ingestive processing by these two species reflects differences in their larval diet. Clearly, my studies show that female caterpillars regulate both nutrient consumption and post-ingestive physiology to accumulate greater reserves.