# Avocado leaf toxicity to microfauna?



## Veneer (Nov 13, 2012)

I was going to germinate some Hass avocados as an supplemental leaf source for my litter-eating inverts, but after digging up the following think I may be calling that off.

You might have heard of avocado (_Persea americana_) toxicosis in birds and mammals (from stem, pit, and especially leaves more so than fruit, but for the most sensitive species even the flesh can be dangerous). There's huge taxonomic variability in response (and the data for vertebrates beyond this is limited – I see some poorly sourced claims of fish dying after avocado leaves blew into their pool) but the most severe reactions are pretty dire – rapid and fatal myocardial necrosis. The main culprit seems to be a lipid-soluble compound unique to this genus called persin, which is especially concentrated in leaf tissues.

Poison is a matter of dose, as the adage goes, and you might wonder if this is a _practical_ grounds for worry for hobby arthropods (basically all plants have defensive chemicals of some sort, and you can certainly find proof of concept literature reporting insecticidal activity for isolates from tried and tested tree species like _Magnolia virginiana_). Unfortunately, I think it could be. (I can't really speculate about downstream effects of using avocado-grazing inverts as feeders.)

The "macroscopic" observation that set it all off – Chang et al. (1975) noticed that silkworms were stunted on fresh avocado leaves:









(Their "active component IIA", toxic to the larvae at 200ppm, was what later workers would dub persin.)

Rodriguez-Saona et al. 1997:



> We isolated and identified (12Z,15Z)-1-acetoxy-2-hydroxy-4-oxoheneicosa-12,15-diene (persin) from avocado as a compound toxic to _Spodoptera exigua_ [Veneer: beet armyworm moth, an agricultural pest] larvae. Persin was obtained from oil extracted from the specialized idioblast cells of avocado fruit. When tested for activity using neonates in no-choice artificial diet bioassays, *persin at concentrations of 200 μg/g inhibited growth*; larvae gained only ∼50% of the weight attained by control insects after seven days. *At concentrations of 400 μg/g or above, larval growth was reduced by >70% as measured by weight gain, and significant mortality occurred.* In choice tests, persin at concentrations of 400 μg/g or higher deterred feeding, with significantly more larvae being found on control diet than on persin-treated diet. Possible applications of persin as a natural insecticide are discussed.


Follow-up work by Rodriguez-Saona & Trumble (2000) argued that defense against generalist insect herbivores is one of the primary functions of the specialized oil cells in which persin is concentrated ... and we already see that avocado has other tricks in its chemical repertoire than just that.

For reference, concentrations of persin (the specific diene in question) in fresh leaves of different avocado cultivars (Carman & Handley, 1999:1330):









That is, fresh leaves of the familiar Hass clock in at 4500 μg/g. 

You'll see that the Mexican cultivars tend to have less than the Guatemalans (though two of the Guatemalan hybrid strains apparently have negligible levels), which sounds in line with mammalian toxicity observations.

The thing is, I know some members of this board have used avocado leaf litter in isopod and spring cultures to no overwhelming ill effect (well, no immediate crashes – I don't think we have real case/control comparisons). I assume these leaves are usually getting added in a dried (and baked?) state and are not the sole leaf litter source – maybe thermal degradation or microbial breakdown dissipates all of these concerns, maybe isopods are better physiologically equipped to deal with these defensive compounds than moths, or maybe people have just been lucky with their avocado cultivars.


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## cam1941 (Jan 16, 2014)

I have been using avocado leaves in my cultures and tanks for a few years now. I have found that not only they harmless but I find that the microfauna absolutely loves them.

Although, the undisputed champion of leaves is still fig leaves (the best) (but any large ficus leaves will work) 

This of course is another type of leaf litter that may be considered suspect due to its milky sap. Just let them dry all the way and you will be amazed with the results.

All of my cultures explode when I have them to add...


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## DPfarr (Nov 24, 2017)

Has anyone ha success with Ericacea members? Coffee or some of the epiphytic blueberries? Also Theobroma cacao? They have many of the same compounds as green tea Camellias.

Currently I've got some huge cacao leaves on my tank floor.


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## Veneer (Nov 13, 2012)

Your reports did take the edge off some of my concerns. Do you just air-dry them at room temperature? 

I am trying out _Ficus septica_.



cam1941 said:


> I have been using avocado leaves in my cultures and tanks for a few years now. I have found that not only they harmless but I find that the microfauna absolutely loves them.
> 
> Although, the undisputed champion of leaves is still fig leaves (the best) (but any large ficus leaves will work)
> 
> ...


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## cam1941 (Jan 16, 2014)

Exactly... I place them in a cardboard box, making sure that they are not wet from cleaning. 

In a couple weeks they should be crispy and ready to go.






Veneer said:


> Your reports did take the edge off some of my concerns. Do you just air-dry them at room temperature?
> 
> I am trying out _Ficus septica_.


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