White Lined Sphinx moths are also known as Hummingbird Moths and the larva of these sphinx moths grow on and eat a variety of what we call "weeds" so they are known as a beneficial moth.
Because the Tobacco, or Tomato, Hornworn is the larva of members of the sphinx moth family many people think all pf the sphinx moth family is a pest, although there are also those that think that the Hummingbird Moths come from the larva of the Carolina Sphinx or the Five Spotted Hawkmoth, both sphinx moths and the parents of the Tobacco, Tomato, hornworm.

So, you're sure about the ID of your Sphinx moth? Just checking. The larvae of most Sphingidae have a horn, making them pretty recognizable; they are often pretty large, as well.

If yours is really the Whitelined Sphinx moth, it enjoys a wide range of host plants, something a bit unusual in this family. I've identified them on oaks and elms, tomatoes, and even portulaca but they can also be
found on many other plants. If populations are high, they can be a pest of tomatoes, grapes, and other crops. Yes...I said tomatoes.

The "beneficial " aspect is complex but you should try to understand it as much as possible. These moths visit an enormous variety of flowers, especially those that become strongly scented at night. Therefore, they are pollinators. It's the larvae that can cause problems IF your crops are their host plants AND they are in large enough numbers. Accurate ID is very important.

As a market grower, you need to find dependable information resources for insect identification. If you can provide pretty good pictures, you have a much better chance at getting some accurate information. Not just here in the Gardenweb but at your Extension office and other places.

I'll be happy to help when I can....just post in here or email.