Submitted to: Journal of Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 1997
Publication Date: N/A
Interpretive Summary: This research describes two new lipid classes which were discovered on the surface of Heliothis virescens pupae that had been fed larval diet containing the mold and yeast inhibitor, sorbic acid. The tobacco budworm, H. virescens, is a serious agricultural pest that burrows underground to pupate. During the pupal stage, insects are completely immobile and do not tfeed, making them extremely vulnerable. Many insects which pupate underground deposit a thick layer of wax on their cuticle which may be their only defense against desiccation, soil microorganisms, and predators. Therefore, knowledge of how the outer waxy coating is deposited could lead to developing a means of controlling agricultural pests and protecting beneficial insects. The presence and quantities of these two new lipids deposited on the cuticle of the pupae was found to be related to the amounts of sorbic acid in the larval diet. The lipids were identified as long chain primary alcohols esterified to sorbic acid or its metabolite, 4-hexenoic acid. Considering the high energy demands of a developing insect, it was surprising to determine that this six-carbon, two double bond acid was not oxidized, but instead was reduced and/or esterified. For devising biocontrol strategies, these results provide useful knowledge toward developing a means of marking laboratory-reared H. virescens moths prior to release and recapture studies.
Technical Abstract: Two previously unreported lipid classes were characterized which are present on the cuticular surface of laboratory-reared tobacco budworm (Heliothis virescens, Fabricius) pupae only when the mold and yeast inhibitor, trans, trans 2,4-hexadienoic acid (sorbic acid) is added to the larval diet. One lipid fraction was identified as esters of sorbic acid and C26, C24, C28, C22, and C30 primary alcohols (listed in descending order of abundance). The second, less polar lipid fraction was shown to consist of esters of 4-hexenoic acid and the same C22-C30 even-chain primary alcohols. The two lipid classes were structurally identified on the basis of their analysis by thin-layer chromatography, gas chromatographic retention times, gas-liquid chromatography-mass spectrometry, infrared and proton magnetic resonance spectroscopy. Results of the same analyses on synthetic compounds, long-chain alkanyl esters of 2-, 3- and 4-hexenoic acids and 2,4-hexadienoic acid, were also presented.