Dietary self-selection by the tobacco hornworm, Manduca sexta: Self-selection from defined diets and the role of the maxillae in this process

Investigations into dietary self-selection by larvae of the tobacco hornworm, Manduca sexta, and the role of the maxillae in this process are presented.The insects were given the opportunity to self-select from two defined diets, both complete except that one contained protein but no digestible carbohydrate and the other contained carbohydrate but no protein. Fourth instars ate the protein and carbohydrate diets in a ratio of 83:17, whereas fifth instars chose an overall ratio of 72:28, protein:carbohydrate. In general, the growth and efficiency of food use of both instars were inferior in the case of self-selectors than that of the controls. Fourth instars held the daily protein:carbohydrate ratio relatively constant. Fifth instars, in contrast, changed their preference ratio.When 4th instars were provided with a nutritionally complete diet with a protein:carbohydrate ratio of 56:44, 70:30, 84:16 or 98:2, they ate the least food and had the highest ECD on the 84:16 diet, "the self-selected ratio". When a 70:30 ratio of protein:carbohydrate was incorporated into a single diet and fed to 5th instars, it promoted a similar efficiency of food use to 56:44 diets. The degree of separation of the diets offered affected the ratio of protein to carbohydrate selected; 1 cm separation appears to be sufficient to affect self-selection behavior.In response to protein dilution in dietary selection, the larvae compensated by consuming more of both the protein-containing and carbohydrate containing diets. In most of the cases, this compensation was sufficient to maintain normal growth. While in response to carbohydrate dilution in dietary selection, they responded by eating more from the protein-containing diet as the sucrose content of the carbohydrate diet declined. The growth and efficiency of food use was little affected over the entire range of carbohydrate diets tested.It has been suggested that dietary self-selection is controlled by changes in peripheral gustatory sensitivity of the maxillary palps. However, the results showed that maxillectomy does not interfere with self-selection for protein and carbohydrate on a short and long-term basis. This suggests that changes in the sensitivity of the maxillary receptors can not be the sole mechanism for mediating self-selection.U of I OnlyETDs are only available to UIUC Users without author permissio