The biosynthetic pathway of neral and its key enzyme(s) in Carpoglyphus lactis were elucidated using a crude enzyme solution obtained from C. lactis. Geraniol, which was biosynthesized via the mevalonate pathway, was first oxidized to geranial, and then geranial was isomerized to neral in C. lactis. Geraniol's geometrical isomer, nerol, was not converted by the crude enzyme solution. The body of C. lactis contained geraniol dehydrogenase (GeDH) dependent on NAD + and a factor that catalyzes the isomerization of geranial to neral. Four GeDHs were found in the crude enzyme solution of C. lactis when subjected to electrophoresis followed by staining with nitro blue tetrazolium and phenazine methosulfate in the presence of geraniol as a substrate. This is the first report of GeDHs from an animal.
The presence of the alarm pheromone was demonstrated in the hexane extract of an acarid mite Tyroborus lini Oudemans 1924. The active fraction derived from an SiO 2 column chromatography of the mite extract was identified as neryl formate, (Z)-3,7-dimethyl-2,6-octadienyl formate by GC/MS and GC analysis. The synthesized neryl formate was shown to be active at 0.05-1 ng dose. Males contained 0.08 ng of the compound on average, and females 0.16 ng on average. The alarm pheromone was a component present in the opisthonotal gland. Once totally discharged from the gland upon disturbance, it took seven days before the pheromone content reached to its original level in the gland, whereas other compounds recovered within 60 hrs. The reason remains obscure at present.
Neral [3,7-dimethyl-(Z)-2,6-octadienal] was identified to be the female sex pheromone of the mite Histiogaster sp. (Acari: Acaridae). The species originated from a fungal Trichoderma harzianum culture in Japan. The compound aroused males to mount females. Although the compound was detected in both sexes (29.4±8.9 ng in females and 5.7±1.9 ng in males), the behavior observation suggested that males could distinguish females from males. Synthetic neral indicated the activity at 0.1-1 ng doses. On the other hand, geranial [3,7-dimethyl-(E)-2,6-octadienal, the geometrical isomer of neral at the 2-C position], did not sexually stimulate males. Males could, therefore, discriminate between neral and geranial. Escaping behavior was observed upon exposure of neral at 100 ng and of geranial at 10-100 ng doses.
Hexane extracts derived from an unidentified Oulenzia sp. showed the alarm pheromone activity. The extract was composed of the following 10 compounds; tridecane, neral, pentadecane, dodecane, 3-hydroxybenzene-1,2-dicarbaldehyde, geranial, (Z)-7-pentadecene and 7-hydroxyphthalide in decreasing order together with two unknown compounds. After fractionation with a silica gel column, the active fraction consisted of a mixture of neral and geranial. Neral was found to show the activity, but geranial was not. Neral was, therefore, identified as the alarm pheromone of this species.
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