Chemistry, biochemistry, and physiology of insect cuticular lipids (original) (raw)
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Cuticular lipids of insects as potential biofungicides: methods of lipid composition analysis
Analytical and Bioanalytical Chemistry, 2011
The main function of cuticular lipids in insects is the restriction of water transpiration through the surface. Lipids are involved in various types of chemical communication between species and reduce the penetration of insecticides, chemicals, and toxins and they also provide protection from attack by microorganisms, parasitic insects, and predators. Hydrocarbons, which include straight-chain saturated, unsaturated, and methyl-branched hydrocarbons, predominate in the cuticular lipids of most insect species; fatty acids, alcohols, esters, ketones, aldehydes, as well as trace amounts of epoxides, ethers, oxoaldehydes, diols, and triacylglycerols have also been identified. Analyses of cuticular lipids are chemically relatively straightforward, and methods for their extraction should be simple. Classically, extraction has relied mainly on application of apolar solvents to the entire insect body. Recently, several alternative methods have been employed to overcome some of the shortcomings of solvent extraction. These include the use of solid-phase microextraction (SPME) fibers to extract hydrocarbons from the headspace of heated samples, SPME to sample live individuals, and a less expensive method (utilized for social wasps), which consists of the collection of cuticular lipids by means of small pieces of cotton rubbed on the body of the insect. Both classical and recently developed extraction methods are reviewed in this work. The separation and analysis of the insect cuticular lipids were performed by column chromatography, thin-layer chromatography (TLC), high performance liquid chromatography with a laser light scattering detector (HPLC-LLSD), gas chromatography (GC), and GC-mass spectrometry (MS). The strategy of lipid analysis with the use of chromatographic techniques was as follows: extraction of analytes from biological material, lipid class separation by TLC, column chromatography, HPLC-LLSD, derivatization, and final determination by GC, GC-MS, matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) MS, and liquid chromatography-mass spectrometry (LC-MS).
Alkanes from surface lipids of sunflower stem weevil,Cylindrocopturus adspersus (LeConte)
Journal of Chemical Ecology, 1984
The stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae) yields 3% of its body weight as extractable lipids (40 #g/weevil). The alkane fraction was composed of n-alkanes (38%) and branched alkanes (62%). The compounds were characterized by gas chromatography-mass spectrometry (GC-MS). The chromatogram contained several single-component peaks (9 of 25). Only seven dimethylalkanes were isolated (17.8%): 9,19-and 9,21-dimethylheptacosane; 9,19-and 9,21-dimethylnonacosane; 9,21-and l l,21-dimethylhentriacontane; and l l,21-dimethyltritriacontane. Important methylalkanes were: 2-methyltetra-and hexacosanes and 10-methylhexa-and octacosanes. Late-eluting gas chromatography peaks were composed of simple alkane mixtures or a single component.
Journal of Chromatography A, 2013
The organic compounds occurring naturally on the cuticles (surfaces) of insects are important for insect communication, help to act as protective water barriers and are useful in chemical taxonomy. Typically the cuticular lipids are only studied by gas chromatography-mass spectrometry (GC-MS) of hexane or pentane extracts, so the normal limitations of GC-MS makes it perhaps unsurprising that compounds with more than about 35 carbon atoms have only rarely been reported. Here we show by high temperature (HT) GC and HTGC-MS of extracts of eleven species of insects from nine genera, that longer chain compounds are actually common. Wax esters and triacylglycerides are virtually ubiquitous in such extracts, but long chain (>C 35) hydrocarbons also sometimes occur. Whilst the latter have occasionally been reported previously from mass spectrometry studies, the use of the HTGC combination with MS allowed even some isobaric isomers to be separated and thus more complete lipid distributions to be monitored. Since the physical properties of cuticular compounds depend on this composition of the mixtures, such differences may influence the water loss rates of the insects, amongst other effects. In addition, the high molecular weight compound profiles may allow species to be more easily differentiated, one from another. It would be interesting to apply these methods to examination of the cuticular lipids of insects on a more routine basis, ideally in combination with MALDI-TOF-MS and imaging methods.
Stereochemistry of Olefinic Bond Formation in Defensive Steroids of Acilius sulcatus (Dytiscidae)
European Journal of Biochemistry, 1977
The defensive secretion of Acilius sulcatus contains a number of pregnane derivatives : cortexone, 20a-hydroxy-4-pregnen-3-one, together with the unusual A 4 s 6 dienes, 6,7-dehydrocortexone, 20ahydroxy-4,6-pregnadien-3-one and 4,6-pregnadien-3,20-dione. The synthesis of all these steroids except cortexone is described. Complete separation of the steroids of Acilius can be achieved by high-performance liquid chromatography on a reversed-phase column system. During biosynthesis of the Acilius steroids from cholesterol, introduction of the A4 and A6 bonds involves elimination of the 48 and 7p hydrogens, respectively. Possible mechanisms of formation of the A4,6 steroids are discussed.
Insect Biochemistry, 1983
Akaraet--The cuticular lipids of the cabbage looper Trichoplusia ni are comprised mostly of hydrocarbons. The type of hydrocarbons present varies with development. Over 98% of the hydrocarbons of the larva and pupa are 2-methyl-and internally branched mono-, di-and tri-methylalkanes of 31-42 carbons. Methylalkanes comprise 74.5 and 86.1% of the hydrocarbons from 3-day-old adult females and males, respectively. Newly emerged adults contain traces of n-alkanes which increase in amount to day 5. No significant increase in methylalkanes was observed in adults with age. Larvae readily incorporated [1-14C]acetate into each major hydrocarbon component, whereas [3H]valine preferentially labelled the 2-methylalkanes and [1-14C]propionate labelled the internally branched alkanes almost exclusively. [9,10-3H]Palmitate was not incorporated into methyl alkanes which was consistent with the methyl branches being inserted early during chain elongation. Adult insects incorporated radioactive precursors into their hydrocarbon at much lower rates than did larvae, and switched from the almost exclusive synthesis of methylalkanes during larval stages to producing only n-alkanes as adults.
Insect Biochemistry, 1989
Four homologous series of very long-chain methyl-branched alcohols were found in the internal lipids of cabbage looper, Trichoplusia ni, pupae both as free alcohols and as esters. These alcohols were identified based on mass spectra of their TMS and acetate derivatives, and on the Kovats Indices and mass spectra of the alkanes obtained by reduction of their bromide derivatives with LiAIH 4. The four homologous series (from C36 to C46) consisted of monomethyl-, two dimethyl-and a trimethyl-branched alcohol series. The major alcohols (with the corresponding alkanes in parentheses) were identified as 24-methyltetracontan-l-ol (17-methyltetracontane), 24,28-dimethyltetracontan-1-ol (I 3,17-dimethyltetracontane), 24,36-dimethyltetracontan-l-ol (5,17-dimethyltetracontane) and 24,28,36-trimethyltetracontan-1-ol (5,13,17-trimethyltetracontane). The minor components had an odd number of carbon atoms (C37, C39, C41 and C43) in the carbon chain and the methylalkanes formed from their reduction had methyl branches on the 18-and 14,18-positions. The methylalkanes found internally in pupae were similar to those previously reported in larval cuticular lipids (de Renobales and Blomquist, Insect Biochem. 13, 493-502, 1983). Additional novel methylalkanes identified were 2,X-dimethylalkanes, 5,15-dimethylhentriacontane, 5,23-dimethyltritriacontane, 5,17,23-trimethyltritriacontane and 5,15,23-trimethylpentatriacontane. The methyl branching positions of the major methyl-branched alcohols were different from those of the major methylalkanes.
Cuticular hydrocarbons from two species of Malaysian< i> Bactrocera fruit flies
1993
The cuticular hydrocarbons of two Malaysian taxa (Malaysia A and Malaysia B) of the Bacb'ocera dorsalis complex were analysed by gas chromatography and gas chromatography-mass spectrometry. Significant quantitative differences in the distribution of hydrocarbons of different chain lengths, mainly the 31-, 33-and 35-carbon backbone compounds of these two species were observed despite indistinct qualitative differences in these hydrocarbons. The cuticular hydrocarbons of Bactrocera Malaysia A and B. Malaysia B (denoted as BMA and BMB respectively) comprised n-alkanes, terminally branched monomethylalkanes, internally branched monomethylalkanes, and dimethylalkanes. Hydrocarbons with the parent chain of 33 carbons predominate in these two species. The most abundant components present in the hydrocarbon mixture of BMA are the isomeric mixtures of (333 internally branched monomethylalkanes while in BMB, are the isomeric mixtures of C33 dimethylalkanes. The major n-alkanes present in both species were n-hentriacontane and n-tritiacontane. The major components of terminally branched monomethylalkanes in BMA were 3-methylhentriacontane and 3-methyltritriacontane, while in BMB was 3-methylhentriacontane. In BMB, the internally branched monomethylalkanes were predominated by isomeric mixtures of C31 and C~. The major dimethylalkanes in BMA were the isomeric mixtures of C33 and C35. Statistical comparisons of the cuticular hydrocarbon compositions of the two species by canonical discriminant analysis show distinct interspecies identities.
Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 1995
The waterproofing abilities of insect cuticular tipids, consisting mainly of hydrocarbons, are thought to depend upon their biophysical properties. However, little is known regarding the effects of specific structural changes upon cuticular lipid properties. We examined the phase behavior of pure hydrocarbons differing in chain length, methyl-branching pattern, and unsaturation, using Fourier transform infrared spectroscopy. Melting temperatures (Tin) of 21-40 carbon n-alkanes increased by 1-3°C for an increase in backbone chain length of one carbon atom. The effects of methyl-branching on hydrocarbon properties depended upon the location of the methyl group along the molecule. Melting temperatures of 25-carbon long methyipentacosanes decreased by over 30°C as the location of the methyl moiety was shifted from the terminal portion of the molecule to more internal positions. Addition of a second methyl branch had additional effects on T m. Unsaturation decreased Tm by 50°C or more.
γ-Dodecalactone from rove beetles
Tetrahedron Letters, 1972
Many staphylinfd beetles possess exocrine glands, yet the secretions of only two species have been identified', the principal components being monoterpenes. A acre complex molecule has been found in the blood of a staphylinfd4. The pygidial secretions of two species of staphylfnids of the genus Bledius contain, in addition to terpenes, a benzoquinone, undecene, and y-dodecalactone, which has not been reported previously fram insect sources. Pygidial glands of Bledius mandibularis and B. spectabilis from the Atlantic coasts of the United States and Europe, respectively5, were excised and imaersed in methylene chloride and the resulting extract analyzed by combined gc-ms6. This revealed the same five components in both species: The mass spectrum of the first component was similar to reported spectra for 1-undecene' and identical to that of an authentic sample. The presence of the terminal double bond wzs confirmed by an absorption at 11.0 or in its infrared spectrum and by ozonolysis to decanal, identified from the mass spectrum of the aldehyde and its methoxime'. Methyl p-benzoquinone (II) was identified by comparison of its mass spectrum with that of an authentic sample. In addition to the parent peak at m/e 122, it exhibited large peaks at m/e 94, 4635