Squash Vine Borers
The number one pest of Summer Squash and one of the worst pests of a plant you are likely to encounter in vegetable gardening. Whereas many pests simply do some damage (often not serious), this one will kill the plant almost every time, unless drastic measures are taken. If you aren’t very observant, by the time the damage is apparent the plant is wilting and close to death.
If a plant starts to wilt, the commonest course of action is to cut the plant open and pry out the worm like caterpillars (I don’t like killing things but it’s hard not to feel some satisfaction when removing these). The borers give away their location by the sawdust-like frass that comes out of little holes in the stem. You might save the plant if you bury the stems in soil, so they can send out new roots. This is a very discouraging pest when it gets bad and can cause you to stop planting Squash. After digging out 8 or 10 borers the plant may be pretty well shredded. Another course of action is to inject B.T into the stem.
It would be much better if you could prevent the borers from entering the plant in the first place. One idea is to lay a sheet of aluminum foil ‘mulch’ under the plant, apparently it is supposed to fool the parent moth so she doesn’t find the stems. You might also wrap the stem with aluminum foil.
Image: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org