Update: Squash vine borers attacked my zucchini, here's how I saved them
My zucchini plants suddenly wilted last Tuesday, and I panicked. After slicing a stem open, I found fat white larvae eating from the inside. I grabbed some Bacillus thuringiensis from the garden store and injected it into the vines with a small syringe. It stopped the borers dead, and the plants are recovering now.