Effects of High‐Fat Diets on Mortality and Feeding in the Tobacco Hornworm Caterpillar, Manduca sexta

Abstract

Nutritionally‐balanced diets are important for fitness, but for insects the high energy value of fat storage is crucial for reproduction and development. Although studies have shown that insects fed high carbohydrate diets have increased fat storage, and excess fat storage in insects may have a fitness cost, little is known about how insects regulate fat consumption when presented with diets containing varying lipid content. To determine how insects respond to high fat diets, we fed caterpillars of different ages high (5.6%), medium (3.4%), or low (0.4%) fat diets. Young Manduca sexta larvae reared on high fat diet had 80% mortality and 43% lower body mass compared to those reared on medium or low fat diets. Older larvae showed no difference in mortality, but those fed a high fat diet had a lower average body mass by the third day of the fifth instar. Growth rates and development time also differed. High fat‐fed caterpillars wandered later than those fed low and medium fat diets. To test the hypothesis that the increased survival of older larvae was due to increased lipid transport, we measured mRNA expression of Apolipoprotein I and II (APO1 and 2), proteins responsible for transporting lipids to the fat body and to various tissues. APO1 and 2 expression did not differ with dietary fat content. In addition, we tested the hypothesis that caterpillars preferentially metabolize fat during the fifth instar. We measured oxygen consumption and carbon dioxide emission of caterpillars fed a high or low fat diet and calculated the respiratory quotient. To determine the mechanism underlying the decrease in body size, we tested the hypothesis that the high fat diet altered feeding. Caterpillars fed a high fat diet indeed ate less, as indicated by a decrease in food consumption and the number and mass of fecal pellets produced. These results suggest that increased dietary fat results in cessation of feeding in these insects. Due to conserved fat metabolism pathways in vertebrates and invertebrates, better understanding of the role of lipids in insects could contribute to knowledge of human metabolic diseases and provide support for using insect models for these studies.Support or Funding InformationThis research was funded in part by NSF EPS‐0447679 and IOS‐0953297 to K.J.G. and NIH National Center for Research Resources 2P20RR0l5566. The contents of this study are solely the responsibility of the authors and do not necessarily reflect the views of the NIH.