Diapause hormone (DH) effectively terminated pupal diapause in Helicoverpa zea. This effect was temperature-dependent. The ED₅₀ of DH for diapause termination was approximately 100 pmol. A C-terminal hepta-peptide, LWFGPRLa, was the core sequence required for diapause termination. Only Glycine was variable in the core sequence, and the amide and Arginine were the most important components needed for terminating diapause. Leucine, Tryptophan, and Phenylalanine at the N-terminus of the hepta-peptide were also critical for activity. The C-terminal Leucine was less important. The threshold dose of DH essential to accelerate fly pupariation was 5 pmol for immobilization/retraction and longitudinal contraction and 10 pmol for tanning. Tensiometric measurements revealed that DH affected neuromuscular patterns of pupariation behavior and associated cuticular changes in a manner similar to that of the fly pyrokinins and their analogs.