In zoology, the segment of the body of an insect to which the wings are attached; the thorax; mesosoma: The alitrunk is found in the higher Hymenoptera, including the true thorax and (fused anteriorly to the thorax) the first abdominal segment.

The middle of the three major divisions of the insect body: In most insects, the mesosoma is the strict equivalent of the thorax; but in the higher hymenoptera, it includes the propodeum (first abdominal segment of hymenopterans, fused to the thorax).