Rubiaceae: Dyestuff, repellents and museum bugs

While analyzing the plants chosen for the CHARISMA project some discoveries are made that might not be relevant to the project but is still quite interesting to share.

Closet repellent

 As it has been published by Japanese allelochemical-researchers some Rubiaceae species (like madder, galium and coffee) produce a component at early age that works as an antifeedant or repellent for weed eating insects and moths. This component, nordamnacanthal, is produced by the young weeds as a systematic defense system which prevents phytophagous pests to feed on them.
Molecular structure Nordamnacanthal
 You might think; ‘Another simple household repellent’ like we use in our closets to drive off unwanted visitor ‘Naphtalene’ prepared for the first time by Carl Gräbe in 1869 who worked for the chemical company Meister Lucius und Brüning (him who funny enough synthesized the orange-red dye alizarin in 1869).

No, no, no, let’s not deviate to synthetic dyestuffs if nature already has made such ingenious repellents since much longer like camphor in Camphorwood, magnolias or cedar wood.

 Nordamnacanthal works in the same way and it was detected in wild madder (Rubia peregrina L.) in hedge bedstraw (Galium mollugo L.) in lady’s bedstraw (Galium verum L.) and in madder (Rubia tinctorum L.).

The dye plant that drives away the bug

Another remarkable component present in some Rubia species and in particular Rubia tinctorum L. (Madder) is lucidin-3-O-primeveroside. This particular component drives off the varied carpet beetle (Anthrenus verbasci L.) called in dutch ‘Museumkever’ because it is considered a pest because it not only scavenges on other dead insects but also hair, feathers, natural fibers and dead skin, it leaves its eggs in tapestries and woolly objects leaving a black corroded areas when it hatches. The larva starts eating immediately after hatching and its never-ending appetite scares museums around the globe. These types of insects are also used for cleaning human skulls by forensic pathologists.
Varied Carpet Beetle ( Bug)
It is not certain why the varied carpet beetle avoids this component, even when this component is present in very small amounts, but it is known that lucidin-3-O-primeveroside generates genotoxic compounds such as lucidin and rubiadin which is reported to be carcinogenic in kidney and liver of rats.

 But why drive off the beetle if it does not eats her?

Well, it was never the intension of the plant to produce lucidin-3-O-primeveroside for its own use but it was forced to produce this component by a bacterium called Rhizobium rhizogenes which is a soil bacterium that causes the ‘hairy root disease’ in rubia species. This bacterium infects the roots and causes them to produce a food source for themselves (lucidin-3-O-primeveroside). This component has a mutagenic effect on the roots that causes them to grow abnormally hairy.

Are there more bacteria who feed on dyes?

Yes. An studie made by the University of Warsaw have observed decolourization ande degradation of natural red dyes by microbial cause. Three bacteria; Bacillus cereus, bacillus vallismortis and bacillus subtilis  who feed on purpurin and alizarin and even deteriorate silk textiles. It sounds very dramatic because these bacteria are present everywhere you can not clear the fibers of bacteria. But something simple as low humidity levels where this objects are stored is able to prevent this bacteria to be activated.

There have been cases of microbial decolourization in humid museums but I did not find any case where the varied carpet beetle has damaged any textile objects dyed with plants of the Rubiaceae family, but it is fascinating to note that rubia and galium species are already being used for centuries and that we now are observing that it was actualy quite a good choice.

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