Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2000
Publication Date: 4/1/2001
Citation: Interpretive Summary: Differentiation of Heliothis virescens and Helicoverpa zea is of value as they attack several of the same crops. In the early larval stages they can not be distinguished. Hydrocarbons are a common component of the surface lipids of all life stages of arthropods and are also found among the internal tissues. However, internal hydrocarbons are seldom studied. Hydrocarbons present on the cuticular surface are synthesized internally by the previous developmental stage, and then there is a selective transfer of internal hydrocarbon components to the cuticular surface. The cuticular hydrocarbons of larvae, adults, and pupae have been shown to be species specific. The internal hydrocarbons are similar, but different, than those found on the surface, and are different between the two species. In addition, the specificity of the biosynthetic pathways and the transport systems is demonstrated by the presence of novel methylalkanes identified in the internal lipids which were not present in the cuticular surface lipids.
Technical Abstract: The internal pupal hydrocarbons of Heliothis virescens and Helicoverpa zea amounted to 123 ug and 304 ug per pupa, respectively. They consisted of n-alkanes (8% and 4%, respectively) and methyl-branched alkanes (88% and 94%, respectively). The n-alkanes ranged in chain length from about 21 to 35 carbons and the methyl-branched alkanes from about 26 to 55 carbons vs. methyl-branched alkanes from 28 to 37 carbons previously reported for hydrocarbons from the pupal cuticular surface. The major n-alkane was heptacosane (3.3% and 1.2%, respectively, in H. virescens and H. zea). The major methyl-branched alkanes in H. virescens were methylhentriacontane (15%), methyltritriacontane (12%) and dimethyltritriacontane (10%), and in H. zea were methylnonacosane (17%), dimethylnonacosane (9%) and methylhentriacontane (20%). Methylalkane branch points were predominantly on odd-numbered carbons as has been reported for these and other species. The branching of the putative methyalkanes with 40 carbon and longer backbones were unusual in that they chromatographed with the monomethylalkanes. They had mass spectra indicative of multiple methyl branches, probably of trimethyalkanes with the first methyl branch on carbon 2 and the second and third methyl branches 16 or more carbons down the chain and separated by a single methylene.