Populating field based on another field in the same form

I am trying to get the text that someone types in one form to show up in the post title automatically. The post title field is hidden.
Here is the page where the form is posted:
http://herbalrepertory.throughwoods.com/post-a-new-herb/

I am creating an herb database where each post is an herb. I would like to have the post title field be dynamically populated by the latin name field.

The latin name field does not show up under the insert form field list under create content template.

It seems like it would be easy to do with shortcode based on the form and field ids.