A selective sweet tooth: The effects of various carbohydrates on the dietary selection of the cockroach Rhyparobia maderae nymphs

Insects have been shown to regulate their feeding behavior based on the nutrient content in their hemolymph. For example, the carbohydrate trehalose acts as a blood sugar in many insects and causes reduced intake of food. This project examines the relationship of various carbohydrates on the feeding behavior of madeira cockroach Rhyparobia maderae nymphs. Nymphs were injected with varying levels of trehalose, and other relevant monosaccharides, including glucose and sorbose to observe the changes in dietary intake. There were three separate concentrations for all sugars: A high concentration (160mM in 1 µl injection into the abdomen), a medium level (120mM), a low level (80mM), and vehicle control (0.7% saline). After injection, R. maderae nymphs (n=30-50 per treatment) were provided with a choice of sucrose and casein diet cubes for 24 hours. The results showed that the various sugars had conflicting effects on the intake of these diet cubes. The trehalose injections seemed to have little to no effect on the casein feeding, but interestingly the 120 mM injection nearly doubled the amount of sucrose eaten. Glucose injections appeared to decrease casein feeding as the concentration got larger, while sucrose feeding decreased significantly with medium and high concentrations. Overall feeding (of both casein and sucrose cubes) increased with the sorbose injections across all levels. Injection of various sugars physiologically altered dietary choice by making the cockroaches feel satiated (glucose) or starved (trehalose or sorbose). Interestingly, these results differed drastically from feeding experiments when similar carbohydrates were offered as food.