A Sabal Palm Tree is a Universe — From a Sap Beetle Standpoint

Sabal palmetto

Arecaceae, the Palm Family

Sap Beetle  Brachypeplus glaber

In the horticultural world vertical gardens became faddish a few years ago.   Nothing new there:   Cabbage Palms invented the concept, some of their trunks being vertical jungles, although other individuals can be bare and clean.   Many Cabbage Palms retain  broken-off leaf bases which turn into hundreds of little natural flower pots filled with spongy detritus.  Somewhere I read a list of around 60 plant species occupying Cabbage Palms, merely in one locality.  Some of the hangers-on are rooted on the ground and climb; others root on the palm itself, especially in those fertile leaf bases.

It is fun to walk and gawk at Cabbage Palms to see who is hanging around, and far more fun to wonder about the interactions among the species.   What nutrients, or toxins,  or hormones from the plants perched up high  wash down the trunk and suppress, or favor, species lower on the totem pole.  Some species may use allelopathy (natural herbicides) drizzling down the trunk to discourage competitors taking hold below.  The nutrient cycling patterns would probably amaze, if only we knew.

Corkystem Passionvine enjoying the palm trunk.

The species distributions up and down the trunks do not seem random, although unraveling suspected patterns may be complex or subtle.  Cabbage Palm ecology runs deeper than meets the eye.  The tree has a lot of hidey-holes, and its microscopic life is no doubt a realm of secrets.   The micro-hideaways are where we are headed now, thanks to a team of entomologists.

Honkin’ big hanger-on…Strangler Fig on the Cabbage Palm.

In 2014 Andrew Cline and collaborators explored a remarkable multi-species ecological web on Cabbage Palms.   Virtually everything I’m about to relate comes from their research, linked below.

Join me now at the senescent flower stalk bases still held on the tree.  Any suburban homeowner dragging the fallen inflorescences from their St. Augustine lawn can see layering around the stalk bases.  During yard cleanup however, we may miss all the fun in the layers, the lair of a sap beetle, Brachypeplus glaber, found in this niche essentially exclusively.  Oh-no, a “sap” beetle!   Does it suck sap and disrespect  our state tree?  No, apparently not, its diet is more complex, and the beetle perhaps even benefits its palm host whose flower stalks are the insect’s entire life-bringing universe.

CLICK to see the beetle

Enter a third species into the plot:   The palmetto scale insect Comstockiella sabalis sheds its skins.   Our sap beetle eats the skins in a handy act of recycling.   Great , now move on:

Now come the fungi.   The beetle has a tight relationship with a yeast, Meyerozyma caribbica.   The beetle, including its larval stages,  lives among the yeasts, eats them, and apparently hosts them as internal symbionts.   The same yeast is a known digestive helper in other insects. The entomologists suspected the yeast to be so potently antifungal  as to be of potential medical interest.

Yeasts are not the only important fungi in the story. The main diet of our sap beetle is filamentous fungi, particularly from the genus Fusarium.  Somehow the yeasts seem to help the beetle deal with the Fusarium.  Maybe they constrain it to a dietary level rather than allowing the pathogenic fungus to overwhelm the inflorescence too rapidly, destroying house and home, although that is 100% my speculation.

Fusarium fungi are plant pathogens, and anything that eats the Fusarium or suppresses Fusarium  might be defenders of the palm.

The tale of the sap beetle et al. can lead to just one “sappy” conclusion.  You guessed it.  Here we have a case where an insect and its yeast associates could protect the tree at its vulnerable growing crown right where infective fungi are most unwelcome.   Would residential applications of insecticides and fungicides disturb an intricate and possibly valuable beete-scale insect-yeast-palm-Fusarium microcosm?    And, by the way, where does that little ecoweb go when you “hurricane prune” a Cabbage Palm’s crown down to just a few leaves?

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A few species hanging around on Cabbage Palms

Algae and Cyanobacteria

Asian Sword Fern

Balsam-Pear

Boston Fern

Cowpea

Creeping Cucumber

Golden Polypody Fern

Grapes

Laurel Fig

Leafy liverworts

Lichens

Mosses of various species

Passionvines

Poison Ivy

Shoestring Fern usually with the moss Octoblepharum

Smilax

Strangler Fig

Tuberous Sword Fern

Virginia Creeper

Whisk-Fern (Psilotum)

 

Today’s primary source:  CLICK