There are a few pests that can cause this — snails, slugs and caterpillars. The issue here is that the Bayer Flower Dust should take care of the caterpillars. The other issue is that the snails and slugs would either still be one the plants or have the ability to crawl away which is unlikely since it is in a hanging basket.

Spider mites can cause problems with impatiens but the leaves usually present a discoloration rather than a striping effect. To check for spider mites use a magnifying glass. This insect is very small and is difficult to see with the naked eye.

I assume the stems are still healthy. So my course of action would be to check the basket after dark for snails and slugs. If you have these pests either pick them off or use Fertilome Elminate to kill them. If spider mites are a problem use a miticide — orthene or malathion can help.

You can also trim the impatiens to encourage new growth.