Parasites of Parasites of Parasites (well, sorta) and Red-Bays

03 Jan

Red-Bay   Persea borbonia

Swamp-Bay  P. palustris

Silk-Bay P.  humilis (P. borbonia var. humilis)


In plant groups with names resembling culinary spices, watch out for nomenclatural confusion.   And when you encounter a species complex where different taxonomists define species differently, shun fool’s arguments.  Not all plant groups have studied textbook definitions of species.   I have no interest in sorting out, pontificating upon, or quibbling over the controversial details of Persea taxonomy and naming.   A little relevant data appears at the end of the post under Notes.   Species complexes can easily generate arbitrary, semi-informed, overly specific pseudo-authoritative classification pronouncements.

Just for sloppy convenience, I’m using the term red-bay to cover all three locally native Persea species.

Persea borbonia (by John Bradford)

Persea borbonia (by John Bradford)

Laurel Wilt Disease, an exotic fungus coming with an Asian ambrosia beetle, has since 2002 marched southward from a foothold Georgia, now spanning the length of Florida to menace our red-bays, avacados, and possibly additional related species.   Because the Internet is loaded with info on this, we’ll move on summarily, providing a link.  Ambrosia beetles are not a genetically cohesive group, but rather an ecological lifestyle association:  they have specialized organs to carry fungal spores into the tunnels they bore into trunks and branches (look for telltale dangling strings of sawdust).  The fungus grows lining the burrow, and the beetle feeds on it.  The fungus clogs the plant plumbing and wilts the plant.

Let’s shift to other pests.  Galls on the leaf blades of all three local Persea species are so commonplace and conspicuous they aid in spotting the plants.  The galls come from the egg-laying of tiny red-bay psyllids, bewilderingly named Trioza magnolia, apparently due to old-time confusion between red-bays and sweet-bay magnolias. (See Notes below.  The bug does not bug magnolias).  Psyllids are small hemipteran sucking insects related to aphids and cicadas.  The nymphs mature under the deformed red-bay leaf margins, where the confined little pests have a waste disposal problem.  Not wishing to foul their own nest, they coat their waste in waxy balls and leave it there.    The nymphs are easy to find, to the benefit of a host of predators.

The galls are ugly, but not to a psyllid.

The galls are ugly, but not to a psyllid.

Psyllids, “plant-lice,” are masters of biological funny business.   They are juice-sucking plant parasites and at the same time are hosts to their own internal “parasites” and symbionts.   Psyllids house bacteria, and the 3-way psyllid-bacterium-hostplant relationships can become complex.    The galls are the tip of the lice-berg.   The psyllid with it sucking mouthparts injects bacteria into the host plant, where the bacteria can cause disease, and presumably can transmit to other psyllids, although the details of all the dynamics need research.   DNA technology will help.

Symbiotic bacteria can live inside the psyllid’s cells, almost as cell components.  Such bacteria have some of the briefest genetic codes known to cellular biology.  The bacteria are not mere parasites; they give back, including essential nutrients, and bacterial toxins useful to the psyllids for defense from all those varmints who hunt them (see above).  The bacterial toxins have stirred interest as antitumor agents for human medicine, and perhaps more promising, the insect-bacterial interdependence reveals an Achilles heel for potential psyllid disruption. In agriculture, they are quite the little troublemakers.

Wouldn’t it be something if those toxin-spewing psyllid-borne bacteria participate in the host shrub’s ecological relationships?     Bacteria introduced via psyllids move across grafts in the plant’s phloem.    Parasitic love vine (related to red-bay in the cinnamon family) invades its victim’s phloem.   Conceivably then, the psyllid bacteria could move from insect to red-bay phloem and onward to love vine phloem?…and there impair the parasitic vine, protecting the red-bay?  Any chance psyllid-infested red-bays are comparatively resistant to love vine attack?   Guilty, pure imagination.

Persea borbonia flowers (by John Bradford). (Flower parts in 3's are not common in Dicots, although characteristic of Lauraceae.)

Persea borbonia flowers (by John Bradford). (Flower parts in 3’s are not common in Dicots, although characteristic of Lauraceae.)

Red-bays have broad soil tolerances thanks no doubt in part to their root antibiotic called borbonol, which confers resistance to some fungal (Oomycete) rots. The crushed leaves are distinctively stinky and probably toxic, yet used a little for culinary flavoring.   Anything bioactive and smelly automatically has history in human medicine.  Red-bays have too many historic uses to list.  Name an ailment.  An interesting application, however, is as sort of folk smelling salts to counter unconsciousness.   Maybe that would help in some in my classes.

Red-bay has mixed relationships with butterflies.   The foliage murders eastern tiger swallowtail larvae, and yet is the chief larval host for the palamedes swallowtail butterfly, which probably derives nasty stuff from the leaf tissue to the butterfly’s defensive benefit.

Before quittin’ a word on the fruit.  It is a little weird, a drupe (stone fruit) about the size of a marble  and black or dark blue sitting on a cup (the calyx) like a golf ball on a tee.  Perhaps more noticeable and important farther north, the fruit persists into the autumn or winter, providing late-season wildlife food.    Must be one mighty fine fruit, as we like the fruit of one closely related species, Persea americana, in our guacamole.

The fruits (by John Bradford)

The fruits (by John Bradford)



The native plants called “bays” are not the bay (laurel) leaves of the kitchen, although today’s plants and bay laurel (Laurus nobilis) all belong to the big spicy cinnamon family (Lauraceae) along with another local native favorite, lancewood (Ocotea coriacea), and more.  Sweet bay magnolia (Magnolia virginiana) is in the magnolia family (Magnoliaceae), not particularly closely related to any of the other “bays” of today, although it too has spicy foliage.  Bay-rum (Pimenta racemosa) is in the Eucalyptus family (Myrtaceae), along with allspice (Pimenta dioica), which in turn is not related to the so-called Carolina allspice (Calycanthus floridus, Calycanthaceae).    See what I mean about kitchen names getting tangled?
Persea is a large genus.  Most modern taxonomists variably interpret the local representatives as two or as three species, although some have seen merely variants of a single species, and others have diced the complex into even more species.  There’s no single “correct” answer.   My favorite general go-to guide on North American taxonomy, Flora North America, recognizes three species as follow:
  1. Red-Bay, Persea borbonia, abundant in our counties, in varied habitats, often hammocks, or coastal dunes, with the hairs on twigs and leaf undersides pressed to the leaf surface and the leaf blades often over 8 cm long. Alternatively interpretable as a mere variant of P. borbonia, if accepted as a separate species,   2. Silk-Bay, Persea humilis (or P. borbonia var. humilis)  has more abundant, silkier hairs especially on the leaf underside, and shorter leaf blades on average.  Silk-Bay is mostly a scrub species and, although abundant in Florida, is absent or nearly so from the area our blog covers.
  2. Swamp-Bay, Persea, palustris, has a broad distribution in our area and beyond in diverse habitats from swamps to woodlands. It differs from the others by kinky hairs jutting out from the twig and leaf surfaces (as opposed to pressed to the surfaces).
Not native to Florida, Persea americana is avocado.

Posted by on January 3, 2015 in Red-Bay


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4 responses to “Parasites of Parasites of Parasites (well, sorta) and Red-Bays

  1. Suellen Granberry-Hager

    January 4, 2015 at 9:03 pm

    I am always fascinated by plant-invertebrate-microbe interactions. This one was especially interesting after seeing the galls on the Red-Bays in the Native Plant ID class last spring.

    • George Rogers

      January 5, 2015 at 6:32 pm

      They’re fun to pop open and see who (and what) is inside.

  2. Kimberly Heise

    October 26, 2017 at 11:08 pm

    Have you seen which type of insects prefer the flowers? Do you think this would be one for the bees? I’m curious to know what native species might prefer it

    • George Rogers

      October 27, 2017 at 4:26 pm

      I do not really know, most likely bees.


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