Differences in black pigmentation in lepidopteran cuticles as revealed by light and electron microscopy

Area of Science:

• Entomology
• Microscopy
• Biochemistry

Background:

• The black pigmentation of insect cuticles is a common but complex phenomenon.
• Understanding the ultrastructural basis of this pigmentation is crucial for insect biology.

Purpose of the Study:

• To investigate the ultrastructural differences in black cuticle pigmentation among various Lepidoptera larvae and pupae.
• To elucidate the mechanisms underlying black pigmentation in insect cuticles.

Main Methods:

• Light microscopy of black cuticles from Lepidoptera larvae and pupae.
• Electron microscopy to analyze ultrastructural features of pigmentation.
• Comparative analysis across different species and life stages.

Main Results:

• Two distinct types of black pigmentation were identified based on ultrastructural differences.
• Type 1: Melanin-like granules in the distal exocuticle (observed in Celerio, Papilio, Phalera).
• Type 2: A homogeneous dark layer in the distal exocuticle, with no correlated ultrastructure (observed in Pieris pupae, Aglais pupae; epicuticle in Pieris larvae).
• Epidermal cell processes transport precursors in Celerio.

Conclusions:

• Black cuticle pigmentation in Lepidoptera is not a uniform process.
• Two primary mechanisms, melanization and sclerotization, are responsible for black pigmentation, differing structurally.
• The specific mechanism employed depends on the insect species and life stage.