Tyrosine hydroxylase- and serotonin-immunoreactive neurons in the thoracic ganglia of the Oriental fruit fly, Bactrocera dorsalis

The thoracic ganglia (TG) of insects are essential neural centers responsible for regulating behaviors such as flight and courtship. These ganglia control thoracic muscle movements through the release of biogenic amines, such as dopamine and serotonin, which modulate motor functions and behavioral outputs. The Oriental fruit fly, Bactrocera dorsalis (Hendel), is a major agricultural pest characterized by strong flight and reproductive capabilities. These traits enable rapid dispersal and population establishment, posing significant threats to crop production. Elucidating the neural mechanisms of flight and mating behaviors in B. dorsalis is crucial for developing effective pest management strategies. However, the functional roles of biogenic aminergic neurons in the TG of this species remain poorly understood. This study aimed to elucidate the role of biogenic amines in regulating flight and courtship behavior by employing immunohistochemical techniques using tyrosine hydroxylase (TH, a rate-limiting enzyme in dopamine biosynthesis) and serotonin (5-hydroxytryptamine, 5-HT) antibodies. Using confocal laser scanning microscopy, we analyzed and identified TH immunoreactive (TH-ir) and 5-HT immunoreactive (5-HT-ir) neurons in the TG. Their axonal projections were reconstructed in three dimensions. We identified 10 5-HT-ir and 10 TH-ir neurons. These neurons were primarily distributed in the ventral regions of the TG, located between adjacent neuromeres. The 5-HT-ir neurons exhibited extensive projections throughout the TG with a bilateral projection pattern. In contrast, TH-ir neurons displayed more restricted projection areas. Notably, the cell bodies and axonal projections of these two neuron types were entirely independent, with no co-localization observed. This study provides a comprehensive map of putative dopaminergic and serotonergic neurons in the TG of B. dorsalis, laying a foundation for future research on their roles in behavioral regulation.