Illness-induced anorexia and its possible function in the caterpillar, Manduca sexta

Area of Science:

• Insect immunology
• Animal behavior
• Evolutionary biology

Background:

• Animals often reduce feeding when sick, a phenomenon known as illness-induced anorexia.
• The evolutionary advantage of this behavior is not well understood across different species.

Purpose of the Study:

• To investigate the adaptive significance of illness-induced anorexia in Manduca sexta larvae.
• To test common hypotheses regarding the functions of reduced feeding during immune challenges.

Main Methods:

• Manduca sexta larvae were injected with bacteria (Serratia marcescens) or bacterial components to induce anorexia.
• Larvae were tested for changes in hemolymph iron, movement, infection susceptibility, and mortality under various feeding conditions.
• Specific diets, including high-lipid, sucrose, and water, were force-fed to assess their impact on survival during immune challenges.

Main Results:

• Illness-induced anorexia did not affect hemolymph iron levels or increase host movement away from potential contamination.
• Force-feeding bacteria did not increase susceptibility to systemic infection.
• Force-feeding a high-lipid diet increased mortality when larvae were challenged with S. marcescens, but not when larvae were fed sucrose or water.
• Short-term food deprivation did not improve survival rates.

Conclusions:

• The results do not support common adaptive explanations for illness-induced anorexia in Manduca sexta.
• A potential conflict between lipid metabolism and immune function is proposed as a factor.
• Further research is needed to elucidate the adaptive role of illness-induced anorexia in both invertebrates and vertebrates.