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Title: A hexamerin protein, AgSP-1, is associated with diapause in the boll weevil

item Spurgeon, Dale
item Sappington, Thomas

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2002
Publication Date: 12/15/2002
Citation: Lewis, D.K., Spurgeon, D.W., Sappington, T.W., Keeley, L.L. 2002. A hexamerin protein, AgSP-1, is associated with diapause in the boll weevil. Journal of Insect Physiology. 48:887-901.

Interpretive Summary: The boll weevil is a major pest of cotton that survives the winter in a state of dormancy called diapause. Although efforts to control the weevil would be enhanced by a better understanding of diapause, this important aspect of the weevil's ecology remains poorly understood. In particular, little is known of the biochemical changes that occur during diapause. Our objective was to identify chemicals in the blood of the boll weevil that reliably indicate whether a given weevil is in diapause. Examination of the blood of diapausing weevils revealed the presence of a specialized storage protein absent from the blood of reproductive (not diapausing) weevils. An antibody (a chemical that reacts specifically with the protein) reacted with the blood of diapausing weevils but not with the blood of reproductive weevils. Also, when the storage protein was present another protein typical of egg production was absent. However, treatment with a juvenile hormone (a chemical that in most insects controls egg production) did not cause diapausing weevils to produce eggs. In further testing the gene responsible for production of the storage protein was identified and described, and was found to be active in fat tissues of both male and female diapausing weevils. Our results suggest the storage protein is a reliable indicator of diapause, and that diapause is not ended by the hormone that controls egg production. These findings provide a method of identifying diapausing boll weevils without killing them, and presents a new tool for use in future studies of diapause.

Technical Abstract: Diapause is an aspect of boll weevil, Anthonomus grandis Boheman, ecology that is critically important to successful management of this serious pest of cotton (Gossypium hirsutum L.). Yet this phenomenon remains poorly understood. In particular, reliable biochemical indicators of the dormancy that would facilitate a better understanding and further study of diapause are lacking. Our objective was to identify and characterize such an indicator by examining the hemolymph composition of diapausing and reproductive weevils. Hemolymph subjected to SDS-PAGE revealed the presence of a 77-kDa hexamerin (AgSP-1) strongly associated with the diapause morphology. An antibody developed from the N-terminal sequence of the first 25 amino acids reacted only with hemolymph from dormant weevils. Also, presence of the yolk protein, vitellogenin (VG), was inversely correlated with AgSP-1, however treatment with a juvenile hormone analog (methoprene) did not activate reproductive development in dormant weevils. Using a genomic DNA library and 3' RACE, two clones were isolated that yielded the complete sequence of AgSP-1 as well as a portion of the 5' untranslated region. Northern blot analysis confirmed the presence of a 2.5-kB transcript for AgSP-1 in the fat body of dormant weevils that was also present to a lesser extent in the fat body of reproductive weevils. Dormant weevils of both sexes showed similar levels of AgSP-1 expression. Presence of the VG transcript was inversely correlated with that of AgSP-1 mRNA. Our data suggests that AgSP-1 is a diapause-specific protein in adult weevils and that juvenile hormone alone is not effective in terminating dormancy.