Trace identification of plant substances by combining gas chromatography-mass spectrometry and direct deposition gas chromatography-Fourier transform infrared spectrometry.

The advantages of combined gas chromatography-mass spectrometry and direct deposition gas chromatography-Fourier transform infrared spectrometry at the same level of sensitivity are demonstrated using an apolar capillary column. This technique was applied to allelochemicals present in minute concentrations. The identification of volatiles in green leaves and an alkaloid is described.

Origin and identification of bacteria which produce kairomones in the frass of Acrolepiopsis assectella (Lep., Hyponomeutoidea).

The volatiles used by the parasitoid Diadromus pulchellus to find its host, the leek moth, are produced by the bacteria developing in the frass of the host larvae. The origin and the nature of these bacteria were investigated. Samples were taken from healthy leeks and from infested leeks in the field, as well as from the frass of larvae reared in the laboratory either on the host plant or on an artificial diet. The various species of bacteria identified were cultured in the presence of precursors of leek sulphur volatiles and their volatile emissions were analysed. Klebsiella oxytoca and various Bacillus, common decomposers of plant matter, were the principal species producing active volatiles which were alkyl disulphides.

Nature and role of sexual pheromones emitted by males ofAcrolepiopsis assectella (LEP.).

Seven compounds that do not exist in the extracts from legs of males have been isolated in the hair-pencil extracts of maleAcrolepiopsis assectella. By combining techniques of GC-MS and GC-FT-IR, six of these compounds have been identified. They are sixn-alkanes: hexadecane (C16), heptadecane (C17), octadecane (C18), nonadecane (C19), eicosane (C20), and heneicosane (C21). Twelven-alkanes of the homologous series, from the C14-C25 compounds were presented to virgin females, mated females, and males. At the end of the scotophase, four of then-alkanes (C16, C17, C19, C21) present in the hair-pencil extract induced the virgin females to adopt the acceptance posture after having induced the virgin females to remain stationary. The two othern-alkanes (C18 and C20) present in the extract have less effect on the females similar to then-alkanes not present in the males. The blends tested do not seem to indicate any synergy between the most active compounds. The threen-alkanes with an odd number of carbons and the C16 compound would thus be the principle components of the male pheromone ofA. assectella. As well as their role of female aphrodisiac, they tend to make males and fertilized females flee.