Thorax

In aptera, from front to back, each segment is larger than the preceding one.

In alates, the thorax is both more strongly developed and sclerotized, especially the mesothorax where the wing muscles are housed.
The exact form of the mesothorax differs depending on the wing position adopted at rest,
The wings are relatively large. At rest they are held above the abdomen, either:

• vertically (the most frequent position – figure A)
• horizontally (Phylloxeridae, Adelgidae, Thelaxinae – figure B)

A : wings held roof-like (Macrosiphum euphorbiae)

B : wings held flat (Thelaxes dryophila)