Labellum

Definition

A fleshy, lobed extension of the prementum in insect mouthparts, typically functioning as a sensory or food-manipulation structure. In Diptera, the labellum forms the paired, sponging or lapping lobes at the tip of the proboscis, often bearing pseudotracheae for liquid uptake; in some Coleoptera and other groups, it serves as a palp-like sensory organ. The term derives from Latin 'labellum' (diminutive of 'labium,' lip), reflecting its position as a small lip-like appendage distal to the ligula.

Etymology

Latin diminutive of labium, 'lip'

Example

In house flies (Musca domestica), the expanded labella bear fine pseudotracheal channels that draw liquid food by capillary action into the food canal.

Synonyms

• labella (plural)
• distal lobes of proboscis (contextual)

Related Terms

• prementum
• ligula
• Proboscis
• pseudotracheae
• hypopharynx
• Mentum
• Maxilla

Usage Notes

Distinguished from the labium proper: the labellum is the terminal, often paired or bilobed portion, not the entire median lower lip. In Diptera, 'labella' (plural) is frequently used when referring to the paired lobes; singular 'labellum' may refer to one lobe or the structure collectively. Not to be confused with the homonymous floral structure in orchids (botany).