Final answer:
The Formosan termite is the most economically important subterranean termite worldwide due to its invasive nature and the severe damage it causes to structures.
Step-by-step explanation:
The most economically important subterranean termite worldwide is the Formosan termite. The Formosan termite is invasive and causes significant structural damage to buildings, trees, and other wooden structures. Due to their aggressive nature and large colonies, they are capable of causing more destruction than the Eastern or Western subterranean termites. Managing and eradicating Formosan termite infestations can be incredibly challenging and costly, which is why they are considered the most economically impactful among subterranean termites.