Potential Correlation Between <i>Bombus lantschouensis</i> Thoracic Morphology and Flight Behavior

Remarkably little modern work has investigated the thoracic structures of insects and their relationship to flight locomotion. Most studies focus exclusively on either morphology or flight kinematics. In this study, we explore within-species variation in mesosomal structures (thorax + propodeum) and their correlation with different flight modes of Bombus lantschouensis. The mesosomal structures, including skeletons and muscles, of four categories-pre-mating queen, post-mating queen, drone, and worker-are examined using micro-CT and 3D reconstruction. Their flight behaviors are also captured using high-speed cameras. Three key kinematic parameters are recorded-wingbeat frequency, flapping amplitude, and average speed-across three flight modes: takeoff, hovering, and forward flight. The wingbeat frequencies of the drone and the worker are higher than those of the queens. The relative distance between the mesophragma and propodeum (DMPP) and the toughness of the mesepisternum, part of the indirect flight system, are related to wingbeat frequency. Flapping amplitude is generally inversely proportional to wingbeat frequency, which might also be influenced by wing shape. After mating, additional fat in the body of the queen increased her weight and possibly compressed her muscles and DMPP, thereby reducing her average takeoff speed. Otherwise, the high diversity of the prothoracic muscles and the pronotal changes might be related to visual capabilities. The changes in the metathoracic muscles connecting to the metacoxal might be related to the functions of the hindlegs. This work provides a basis for future comparative work on bumblebee morphology and biomechanics.