Morphological Characterization of Abdominal Neuromuscular System of Aedes aegypti Larvae.

Mosquitoes are major disease vectors that pose significant threats to human health. Recent efforts to understand the neurobiology of these insects have utilized modern research tools to advance our knowledge of the neural circuits underlying ecologically relevant behaviors in adults. However, the neurobiology of mosquito larvae remains relatively unexplored. This report focuses on the neuromuscular system of mosquito larvae, providing a morphological analysis of the abdominal neuromuscular system in Aedes aegypti. We identified 24 muscle fibers per hemi-segment and detailed their anchoring points and orientations. Using immunocytochemistry, the organization and innervation of abdominal body-wall muscles were reconstructed. Two primary nerve branches emerged from the ventral nerve cord in each segment. The branches, trajectories, and targets of the two primary nerves were named and described. At the synaptic level, motor axons arborization on muscle fibers were quantitatively analyzed. Motor axons branched extensively on muscle fibers, covering up to 90% of large fibers' length and approximately 30% of small fibers. Varicosities along axonal branches showed considerable size variation, with antibody labeled active zones present in all varicosities. Furthermore, active zone densities per varicosity on smaller muscle fibers were significantly higher than those on larger fibers. These observations provide a functional and morphological framework for understanding the physiology of mosquito larval locomotion.