Submitted to: Journal of Environmental Entomology
Publication Type: Book / Chapter
Publication Acceptance Date: November 20, 1997
Publication Date: N/A
Interpretive Summary: Because of problems associated with conventional pesticides such as buildup of toxic residues in the environment, there is a critical need for new concepts and alternative approaches in controlling such pests. The basic premise of this research is that neuropeptides (short chains of amino acids) serve as internal messengers in insects to regulate vital functions such as water balance and muscle movement. Peptides themselves are unsuitable for use in insect control because of their inability to penetrate the tough outside skin (cuticle) of insects. However, peptide-like chemicals called mimics can perhaps be made that could penetrate the cuticle and therefore effectively disrupt the internal environment of the insect and kill it. In this paper we discuss mimics of one class of insect neuropeptides that demonstrate the unprecedented ability to penetrate the insect skin and force the tobacco hornworm moth to ounnaturally produce certain natural body chemicals over a prolonged period of time. Also, these mimics demonstrate resistance to the processes insects normally use to destroy the natural peptides. In some insects this could exhaust the pests' supply of these natural body chemicals and lead to disruption of reproduction. Because this class of neuropeptides also regulate the processes of digestion and development, the mimics presented here are favorable candidates for the development of control strategies based on these other critical insect life functions as well.
Technical Abstract: Amphiphilic pseudopeptide analogs of Phe-Thr-Pro-Arg-Leu-NH2 (FTPRLamide) representing the active C-terminal core of the pyrokinin class of insect neuropeptides, were synthesized either by replacement of phenylalanine with 2-carborane-ethanoic acid or hydrocinnamic acid, or attachment of the hydrophobic groups 6-phenylhexanoic acid (6Pha), 9-fluoreneacetic acid (Fla), 1-pyrenebutyric acid (Pba) and a complex of 2-amino-7-bromofluorene and succinic acid (Abf-Suc) to the N-terminus of the pentapeptide. Three of the pseudopeptides were found to stimulate sex pheromone biosynthesis when injected into females of the moth Heliothis virescens with greater potency than the native 33-membered hormone PBAN. With an ED50 of 0.024 and an EDmax of 0.1 pmoles/female, the analogue Hca-TPRLamide proved to be 50 fold more potent than the natural PBAN. Topical application of each of the pseudopeptides in water to the cuticle of moths stimulated significant production of pheromone. The parent peptide, FTPRLamide, failed to stimulate significant production of pheromone when applied topically. Temporal studies indicated that Hca-TPRLamide stimulated significant production of pheromone for only 4 hr after application whereas continuous pheromone production for 20 hrs was observed when aqueous solutions of either Pba-FTPRLamide or Fla-FTPRLamide were applied to the abdominal surface. The results show that modification of the C-terminal active core of the insect pyrokinins can result in production of pseudopeptides which effectively penetrate the insect cuticle and have prolonged physiological effects. These characteristics make them favorable candidates for use in development of alternative strategies for pest insect control.