Now that I've reared this species and have some additional knowledge, it's tantalus ;) - important to note that these are not final instar, and the horn color is not what it would be in that instar.

Moved from Tantalus Sphinx.

Moved from Tantalus Sphinx.

Moved from Aellopos.

Moved from Sphinx Moths.

This is probably A. titan, but without a photo of the final instar I'm hesitant to move it... but generally A. tantalus has significantly more white streaking. It is however Aellopos, so I will move it to the genus level. While there haven't been records of A. titan from Casasia, it is in the Rubiacea, and therefore isn't out of the question.

Moved from Butterflies and Moths.

Moved from ID Request.

Interesting find, Aellopos tantalus would be my best guess too. A. tantalus is the only sphingid I know of that feeds on Casasia clusiifolia and these larvae look like they could be tantalus, however I have only seen one other photo of this species as a larvae, and this species is variable. Therefore, I cannot be certain that this is tantalus, but I think it could be. Perhaps someone else would have a better idea.

If this is tantalus, it would be the first larval images of the species for the guide. You wouldn't happen to have any images of the final instar would you?