Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2003
Publication Date: 9/22/2003
Citation: NELSON, D.R., LEOPOLD, R.A. COMPOSITION OF THE SURFACE HYDROCARBONS FROM THE VITELLINE MEMBRANE OF DIPTERAN EMBRYOS. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. 2003. v. 136(2)B. p. 295-308. Interpretive Summary: Cryopreservation of insects is becoming a major focus in maintaining genetic diversity, preserving genotypes from genetic research programs, stockpiling biocontrol insects until needed for release, and combating genetic drift in mass rearing programs. Cryopreserved insects can be used to reestablish rearing programs, to help mass rearing programs operate on a more continuous level of production, and to markedly lower insect maintenance costs by eliminating the need to maintain specific lines of germplasm by continuous rearing. Cyropreservation of most cells, tissues and embryos requires that freezable cell water be replaced with a cryoprotectant such as ethylene glycol, dimethyl sulfoxide or glycerol. Insects depositing their eggs into harsh environments equip the eggs with elaborate eggshells and membrane barriers to contend with changes in temperature, moisture, and possible microbial attack. These barriers must be removed to accommodate the requirements for successful cryopreservation of insect embryos. Insect egg shells are easily removed by sodium hypochlorite treatment. However, an impermeable lipid or waxy layer remains on the vitelline membrane of the exposed embryo which can be removed by organic solvents, i.e., hexane. Once the lipid layer is removed, chemical cryoprotectants and water can move across the vitelline membrane. In this study, hydrocarbons were the major lipid class extracted by hexane from the vitelline membrane. We characterized the individual components of this major lipid class of 6 species: the house fly, green bottle fly, sheep blow fly, New World screwworm, secondary screwworm, and the Mexican fruit fly. Lipid classes were determined by thin-layer chromatography and the hydrocarbon components by gas chromatography-mass spectrometry. Unsaturated hydrocarbons were abundant only in the Mexican fruit fly. We suggest that these differences between species may correlate with the ease of membrane permeabilization using solvents and also with the probability that desiccation might occur following oviposition in or upon various media.
Technical Abstract: Hydrocarbons were the major lipid class extracted by hexane from the vitelline membrane surface of dechorionated eggs of the house fly, Musca domestica, the New World screwworm, Cochliomyia hominivorax, the secondary screwworm, Cochliomyia macellaria, the green bottle fly, Phaenicia sericata, the sheep blow fly, Lucilia cuprina, and the Mexican fruit fly, Anastrepha ludens. Long-chain n-alkanes comprised the major lipid class removed from vitelline membranes of all species except A. ludens in which 2-methylalkanes were the major class. The range in size of the hydrocarbons was: in the New World screwworm, Cochliomyia hominivorax (C23 - C49), the secondary screwworm, Cochliomyia macellaria (C27 - C33), the sheep blow fly, Lucilia cuprina (C24 - C35), the house fly, Musca domestica (C25 - C36), the green bottle fly, Phaenicia sericata (C25 - C33), and in the Mexican fruit fly, Anastrepha ludens, (C21 - C51). The major hydrocarbon component, expressed as percent of the total hydrocarbons, was n-nonacosane (C29) in C. hominivorax (40%), C. macellaria (43%), L. cuprina (38%), M. domestica (39%), and P. sericata (60%). However, in A. ludens, 2-methyloctacosane (32%) was the major hydrocarbon. Unsaturated hydrocarbons, monoenes (16%) and dienes (11%), were abundant only in A. ludens. Since prior studies indicate that the length of time the embryos must be exposed to hexane with or without a small amount of alcohol in order to attain permeability is species dependant, we suggest that the differences in lipid classes may contribute to this variation in lipid extractability.