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Fat Stunts Growth of Tobacco Hornworm Caterpillars

Studying caterpillars can improve understanding of metabolic diseases in humans

San Diego (April 4, 2016)—Tobacco hornworm caterpillars eating a high-fat diet are smaller than their counterparts eating a medium- or low-fat diet. New research presented today at the Experimental Biology 2016 meeting in San Diego found that fat decreased the caterpillars’ food consumption, leading to the smaller body size.

Credit: Gita Thapa

Tobacco hornworm caterpillars on high-, medium- and low-fat diets (left to right) for three days. The low-fat diet is the standard diet for tobacco hornworm caterpillars kept in a lab.

Fat metabolism pathways are similar among vertebrates, including humans and invertebrates such as the tobacco hornworm caterpillar. According to the study’s authors, understanding the role of fats in insects could help understand human metabolic diseases.

Fat is important for reproduction and development in insects. While insects with a high-carbohydrate intake have greater fat stores, little is known about what happens when insects eat fat. Researchers from North Dakota State University fed tobacco hornworm caterpillars of different ages low-, medium- or high-fat diets. They found that 80 percent of the young larvae raised on the high-fat diet died. The larvae’s body mass was 43 percent lower than the body mass of larvae fed low- and medium-fat diets. Development was also slower: Caterpillars on the high-fat diet started wandering later than their peers fed low- and medium-fat diets. Older larvae on the high-fat diet fared better. They had similar mortality rates as their counterparts on low- and medium-fat diets, but they also grew more slowly.

The researchers found that fat-fed caterpillars had a smaller body size because they ate less overall. The researchers measured lower food consumption and fewer fecal pellets produced. “The results suggest that increased dietary fat results in cessation of feeding in these insects,” according to the researchers.

Kendra Greenlee, PhD, associate professor at North Dakota State University, will present “Effects of High-Fat Diets on Mortality and Feeding in the Tobacco Hornworm Caterpillar, Manduca sexta” as part of the poster session “Comparative Nutritional and Dietary Physiology” Monday, April 4, from 12:45 to 3 p.m. PDT in Exhibit Halls A-D of the San Diego Convention Center.

Full 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.

NOTE TO JOURNALISTS: To schedule an interview with a member of the research team, please contact Stacy Brooks or (301) 634-7209.

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About Experimental Biology 2016

Experimental Biology is an annual meeting comprised of more than 14,000 scientists and exhibitors from six sponsoring societies and multiple guest societies. With a mission to share the newest scientific concepts and research findings shaping clinical advances, the meeting offers an unparalleled opportunity for exchange among scientists from across the United States and the world who represent dozens of scientific areas, from laboratory to translational to clinical research. www.experimentalbiology.org 

Physiology is the study of how molecules, cells, tissues and organs function in health and disease. Established in 1887, the American Physiological Society (APS) was the first U.S. society in the biomedical sciences field. The Society represents more than 10,500 members and publishes 15 peer-reviewed journals with a worldwide readership.

 


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