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Bug of the Month: August pt. 1 – Phylloxera

By August 1, 2018No Comments

Written by Collin McMichael, Education Coordinator

Phylloxera? In my pecan tree? It’s more likely than you think.  I’m sure you might be wondering why Collin has been given the option to write two Bugs of the Month because one was enough.  Well, it just so happens that there is this minute little beasty that has been terrorizing my favorite nuts: pecans. Luckily, this is text and not spoken so you cannot tell instantly that I am not from here since I call them “peh-CAHNS” instead of “PEE-cans”, you big bunch of weirdos.  Anyway, the parasitic plant pest I plan on painting a pretty picture of for you people is a pecan phylloxera. And much like my alliterative forward momentum, phylloxera can stop plants in their tracks.

Phylloxera might sound like something you contracted in college, but they are actually very small, plant-dwelling vexations in the insect order Hemiptera.  If you have been a continued reader of Bug of the Month, you might already know that Hemipterans are the true bugs, a group of insects with piercing-sucking mouthparts.  Phylloxera, however, belong to a smaller suborder along with aphids known as Sternorrhyncha, a sister group to the Auchenorrhyncha to which cicadas belong (more on them next month!).  Unlike cicadas, phylloxera are nearly microscopic. They feed on the leaves and roots of plants, often forming protective galls around themselves by high-jacking plant cellular pathways.

Galls are both unsightly and often detrimental to the plant as they impede normal functions.  Galls can be formed by fungi, viruses, mites, or various other means, but those formed by insects happen after the insect has injected a sort of growth regulator into the plant.  This chemical takes over normal plant development pathways and forces the plant to grow something analogous to, but much less disgusting than, a warty tumor. Generally, inside these botanical aberrances insects are able to find safety from roving predators and gorge themselves on the sugary foodstuffs they convinced the plant to provide for them.

Once a gall is formed and a female phylloxera is safely inside, this fundatrix, or stem-mother, begins a wild parthenogenetic orgy of reproduction, spraying babies all over the place.  Many stay in the gall, but some will leave and then it gets weird. Phylloxera are known to have intensely complicated lifecycles, alternating hosts, body plans, or more for each generation.  Sometimes they are sexual, sometimes they are asexual, and sometimes they do both. Trying to nail down a general life history for a phylloxera is about a difficult as trying to explain why “phonetic” has a ph-.

Two notable crops that regularly experience phylloxera outbreaks are grapes and, as you might have guessed from the introduction, pecans.  The grape phylloxera is certainly more well known as this particular beasty nearly ended wine production in Europe in the 19th century.  Thankfully, since a world without wine is no world for me, the Americans came to Europe’s rescue.  American vines that is. It turns out that American grape rootstock is resistant to phylloxera infestation.  Grafting European vines to American roots gave us our modern wines and destroyed the grape phylloxera’s ability to transition between root and leaf feeding.

The pecan phylloxera does not have such an elegant fix, unfortunately.  In fact, there actually seem to be several pecan phylloxeras. Phylloxerae? Now I’ve lost my train of thought because I just spent longer than I would care to admit looking up etymology stuff.  Regardless, the phylloxeran palate seems mutable and heavily dependent on both phylloxeran species and the genetic makeup of individuals. Whether it be younger plants or those longer in the tooth or perhaps the difference between snacking on stems and lunching on leaves, when it comes to those nut trees that belie my transplant status, stem galling phylloxera seem to be those that cause the most damage.  This particular location weakens branch strength and can cause the young pecans to break off. Phylloxera cannot be controlled as the outbreak happens when adults are protected from insecticidal sprays by their leafy galls. Only spraying on a very specific seasonal schedule has proven an effective strategy against these pests. This maximizes the amount of possible contact with insecticide for the phylloxera and minimizes the amount of pesticide needed to treat the offending orchard.  A veritable win-win!

Click here to read August’s BOTM pt. 2