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Wikipedia's Carmine begins:

Carmine (/ˈkɑːrmən, ˈkɑːrmaɪn/) – also called cochineal (for the insect from which it is extracted), cochineal extract, crimson lake, or carmine lake – is a pigment of a bright-red color obtained from the aluminium complex derived from carminic acid.1 Specific code names for the pigment include natural red 4, C.I. 75470, or E120.

1 Dapson, R. W.; Frank, M.; Penney, D. P.; Kiernan, J. A. (2007). "Revised procedures for the certification of carmine (C.I. 75470, Natural red 4) as a biological stain". Biotechnic & Histochemistry. 82 (1): 13–15. doi:10.1080/10520290701207364

Wikipedia's Dactylopius; Cochineal dye includes the image below of a ~5mm individual Dactylopius confusus that's been squished and a finger covered in a bright red dye thereby "extracted" from it.

And my guess is that the central aluminium may in fact be necessary to produce such a strong absorption of green and blue light (λmax = 530–335 nm).

But it's not yet clear to me where the aluminum for complexing comes from. Is it in the insect's diet and the "aluminium complex derived from carminic acid" is performed inside the insect itself? If so, from where do these insects get their aluminum in such large quantities how do they handle it safely?

Question: Do cochineals ("scale bugs") form aluminium complexes themselves? Where do they get such large quantities so quickly and how do they handle it safely?

"so quickly" because they seem to be pretty short-lived and I'd expect that bio-available aluminum would be pretty scarce.

The reason I ask is because biological aluminum has a toxicity aspect and it doesn't seem to me that it's something you'd particularly get a lot of sucking on plant juice.


Figure 2. Salasaca dyer showing red woollen cloths with modified cochineal red colours. Ecuador. Photo: A. Roquero. from Ana Roquero (2008) Textile Society of America Symposium Proceedings "Identification of Red Dyes in Textiles from the Andean Region" "Dactylopius confusus crushed scale insect, Fort Collins, Colorado, United States" from Wikimedia

Click figures for full size. above first: "Figure 2. Salasaca dyer showing red woollen cloths with modified cochineal red colours. Ecuador. Photo: A. Roquero." from Ana Roquero (2008) Textile Society of America Symposium Proceedings Identification of Red Dyes in Textiles from the Andean Region above second: "Dactylopius confusus crushed scale insect, Fort Collins, Colorado, United States" from Wikimedia. below first: "scale bugs" on my houseplant, perhaps female Dactylopius confusus or Dactylopius coccus, from Are these little white fuzzy insects "scale"? What species and what is their lifecycle like? below second: Structure of carmine from Wikipedia

is this a scale bug (northern Taiwan nursery plant) Structure of carmine

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  • $\begingroup$ companion question: Are these little white fuzzy insects "scale"? What species and what is their lifecycle like? $\endgroup$
    – uhoh
    Commented May 29, 2022 at 1:00
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    $\begingroup$ I gather it's in the diet of O. ficus-indica which does the binding, but I can't pin down the mechanism. I'll give it more time tomorrow, see if there's anything more detailed to find on the topic. $\endgroup$ Commented May 29, 2022 at 2:28
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    $\begingroup$ Definitely something to do with the Al. You get 2 carminic acids to 1 Al and the colour of the carminic acid alone is not bright red, more a deep orange. See article here $\endgroup$
    – bob1
    Commented Jul 17, 2022 at 20:51
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    $\begingroup$ Interestingly ionic salts produce other colours - substitute Na and you get indigo/deep blue, K and Ca salts are red to purple (may also contain Al I though) and ammmonium is blueish red. I'm having difficulty finding anything about the salts without Al though. $\endgroup$
    – bob1
    Commented Jul 17, 2022 at 22:13
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    $\begingroup$ pH dependent I would have thought. Wood ash = potassium salts, though I guess others present too. $\endgroup$
    – bob1
    Commented Jul 17, 2022 at 22:52

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Aluminium moves within plants as a complex with ligands such as oxalate, malate, and citrate.

Plant cells also hide the aluminium (and other junk) in vacuoles. That is most likely the immediate source for the beetle.

Plant roots exude malate and citrate to neutralise aluminium before it poisons the roots. I got this from The role of solute transporters in aluminium toxicity and tolerance.

The toxicity of aluminium is greatly dependant on its form and what it is complexed with. The more "naked" the ion is, the more toxic.

The toxicity is pretty much confined to the roots, and gets more nasty if the pH gets down to 4.3. Once inside the plant it is usually complexed, and not a big problem.

An easily readable review article on toxicity is Aluminum, a Friend or Foe of Higher Plants in Acid Soils.

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  • $\begingroup$ This is all really interesting and mostly new to me, thank you! $\endgroup$
    – uhoh
    Commented Jun 20, 2022 at 19:00

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