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Title: Mode of action of an insect neuropeptide Leucopyrokinin (LPK) on pupariation in fleshfly (Sarcophaga bullata) larvae

item Nachman, Ronald

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2002
Publication Date: 10/11/2002
Citation: Zdarek, J., Myska, P., Zemek, R., Nachman, R.J. 2002. Mode of action of an insect neuropeptide Leucopyrokinin (LPK) on pupariation in fleshfly (Sarcophaga bullata) larvae. Journal of Insect Physiology. 48:951-959.

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 internal 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 work that increases our understanding of the mechanism of the formation of an intermediate stage in the transformation of immature flies to the adult stage. Through detailed analysis of muscular activity, the work reveals that the neuropeptide "LPK" accelerates the switch from wandering to immobilized behavior in immature flies, and requires the cooperation of the nervous system in one aspect, but not in another aspect, of the development of the mature fly. A deeper understanding of how LPK interferes with the process of development will aid in the design of strategies to disrupt the life cycles of pest flies. 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: An insect neuropeptide leucopyrokinin (LPK) (pQTSFTPRLamide) accelerates pupariation in wandering larvae of the fleshfly Sarcophaga bullata. The period of sensitivity to the action of LPK begins approximately 4 h before pupariation. Within this period the degree of acceleration of contraction into the shape of a puparium is practically independent of the age at which the larvae are injected, while acceleration of tanning is distinctly more age dependent. From the ligation experiments we conclude that intact central innervation is essential for the action of LPK on puparial contraction, whereas central neurones take no part in mediation of LPK action on tanning of the cuticle. An analysis of tensiometric recordings of muscular activity revealed that the actual time of LPK accelerated puparial contraction coincides with the beginning of the immobilization/retraction phase. LPK accelerates the switch from wandering behavior to immobilization/retraction behavior but has no effect on the onset and duration of motor patterns that normally underly puparial contraction in controls. The morphology of an accelerated puparium is normal but its formation is temporally dissociated from normal `contraction patterns¿ that are performed a long time after the puparium has contracted. It means that neuromuscular activity of larvae accelerated by LPK does not cease upon formation of the white puparium, but continues until the whole motor program of pupariation behavior is completed. Apparently the peptide acts on the integument by stimulating it to contract and shrink, and no specific patterns of muscular contractions are needed to properly shape the puparium. This finding sheds new light on our understanding of the mechanism of puparium formation.