Squash Vine Borer
The adult fly looks like a moth. It flies during the daytime and lays eggs singly at the base of the squash plants or on leaf petioles. The squash vine borer overwinters as a pupa in the soil and appears in mid June to July. The egg hatches in 7-10 days and larva bore into the stem of the plant leaving a trail of waste behind where it feeds on the stem tissues. The damaged stem tissues cannot facilitate translocation of water and nutrients. This causes the vine to wilt and the whole plant may eventually die. The infestation is more serious during the extended dry period in early summer. Squash that still vine can be kept alive by rooting the stem every foot or so along the vine.
Use row covers, spray with recommended insecticides before the larvae burrow into the stem, and scout the crop (applies to both commercial and homeowner) from mid June onwards for eggs and larval feeding. See pictures (Plant wilting due to squash vine borer damage)