Biochemical Analysis of Insect Camouflage in Manduca sexta, the Tobacco Hornworm
Manduca sexta (Tobacco Hornworm) larvae exhibit diet-induced adaptation, demonstrating green coloration in their natural environment but becoming a pale blue when placed on a lab diet lacking plant material. I hypothesized that the color change observed in the Tobacco Hornworm was induced by the dietary intake of a plant pigment of orange or yellow color (specifically ?-carotene). The pigment ?-carotene is highly hydrophobic, so I hypothesized that it was traveling to the skin via a lipoprotein transport pathway. Hornworms were reared and then bled to extract hemolymph. Ultracentrifugation was used to float out the lipoproteins from the hemolymph. Lipoprotein isolation was confirmed by gel electrophoresis. The lipoproteins isolated from plant-fed insects did indeed contain a bright yellow pigment. UV-visible spectroscopy supported ?-carotene as the pigment being carried by the lipoproteins and responsible for inducing the insect’s color change.