Mesonotum

Definition

The dorsal (upper) sclerite of the mesothorax, the middle segment of the insect thorax. It bears the forewings in winged insects and, in many orders, forms the largest part of the visible thoracic dorsum. In Diptera, Hymenoptera, and Lepidoptera, the mesonotum is hypertrophied and subdivided into an anterior mesoscutum and a posterior scutellum; the wing base is often protected by a small associated sclerite called the tegula.

Etymology

Greek meso- (middle) + noton (back)

Example

In house flies (Diptera), the greatly enlarged mesonotum dominates the thoracic dorsum and carries the single pair of functional wings; the reduced hindwings are modified into knob-like halteres that attach to this structure.

Synonyms

• mesothoracic notum

Related Terms

• Mesothorax
• mesoscutum
• scutellum
• tegula
• pronotum
• Metanotum
• notum
• Sclerite

Usage Notes

The mesonotum is often the most conspicuous part of the thorax in winged insects and is frequently used in identification keys. In Coleoptera, the mesonotum is largely concealed beneath the pronotum and elytra, with only the scutellum typically visible as a small triangular plate between the wing bases. The term is specific to hexapods; other arthropod groups use different nomenclature for homologous structures.