Fig. 2: Melanization pathways in insects.
In Anopheles female mosquitoes, melanin synthesis relies mostly on dopamine produced from the blood meal-derived phenylalanine; however, other precursors from plant sources such as tyrosine or L-DOPA are used by both female and male mosquitoes for the generation of this biopolymer. Most melanins synthesized in insects derive from L-DOPA or dopamine in a reaction initiated by phenoloxidases present in the hemolymph; however, there is one possible minor pathway from a degradation product of dopamine: 3,4-dihydroxyphenylaldehide (DOPAL). DOPAL is a highly unstable compound that reacts with primary amines, leading to protein crosslinking and inactivation. Current literature suggests that its toxicity outweighs its benefits; evidence for DOPAL melanin formation in any biological system remains to be established. Simultaneously but via an independent pathway, dopamine serves as substrate for a process known as sclerotization which promotes hardening of insect cuticles (exoskeleton) and prevents desiccation, dehydration, and invasion by foreign organisms. This process is catalyzed by cuticle-bound phenoloxidases12,17. Created in BioRender. Camacho, E. (2025) https://BioRender.com/d90z642.
