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Title: Diapause hormone in the corn earworm, Helicoverpa zea: Optimum temperature for activity, structure-activity relationships, and efficacy in accelerating flesh fly pupariation

item Nachman, Ronald

Submitted to: Peptides
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2007
Publication Date: 2/15/2008
Citation: Zhang, Q., Zdarek, J., Nachman, R.J., Denlinger, D.L. 2008. Diapause hormone in the corn earworm, Helicoverpa zea: Optimum temperature for activity, structure-activity relationships, and efficacy in accelerating flesh fly pupariation. Peptides. 29:196-205.

Interpretive Summary: Because of problems with the development of resistance to conventional pesticides, there is a critical need for new concepts and alternative approaches in controlling insect pests. The basic premise of this research is that neuropeptides (short chains of amino acids) serve as potent messengers in insects to regulate vital functions. New, selective control measures may be developed by designing metabolically stable mimics of these neuropeptides that actively inhibit or over-stimulate functions regulated by them, resulting in disruption of the internal environment of the insect. We report on the determination of the optimal temperature at which the diapause hormone neuropeptide elicits termination of a hibernation-like state that enhances winter survival in corn earworm moths. In addition, the work identifies components of the structure of the diapause hormone critical for its regulation of this winter survival state. The above results suggest that development of metabolically stable versions of the diapause hormone could lead to agents capable of disrupting this important survival mechanism in these agricultural pests. The work brings us one step closer to the development of practical neuropeptide-like substances that will be effective in controlling pest insects in an environmentally friendly fashion.

Technical Abstract: Diapause hormone (DH) effectively terminated pupal diapause in Helicoverpa zea. This effect was temperature-dependent, with an optimum of 21 degrees C. The dose-response curve indicated an ED50 of DH for diapause termination of approximately 100 pmol. The core sequence and essential amino acids were determined by bioassays using modified and truncated DH analogs. A C-terminal hepta-peptide, LWFGPRLa, was the core sequence required for diapause termination. Activity was lost when Alanine was substituted for any of the amino acids in the hepta-peptide, with the exception of Glycine. A fragment series of analogs suggested that 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: deletion did result in decreased activity, although it could not be substituted by Alanine. The fact that a portion of the DH sequence is similar to the pyrokinin that accelerates fly pupariation prompted us to also evaluate the capability of DH to accelerate development in the flesh fly, Sarcophaga bullata. The threshold dose of DH essential to accelerate fly pupariation was 5 pmol for immobilization/retraction and longitudinal contraction and 10 pmol for tanning, approximately one or two orders of magnitude lower than the effective dose required for diapause termination in H. zea. 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.