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Bill Pramuk
Great fleas have little fleas upon their backs to bite ‘em,
And little fleas have lesser fleas, and so ad infinitum.
And the great fleas themselves, in turn, have greater fleas to go on;
While these again have greater still, and greater still, and so on
(‘Siphonaptera’)
That little poem from "A Budget of Paradoxes" by Augustus De Morgan, came to mind when a reader sent me a photo of a tiny insect they found in an oak leaf gall — the cynipid gall wasp that defoliated so many live oaks in and around Napa in the past year.
Technically, “Siphonaptera” is an order of insects containing about 2,500 species of fleas. I take it De Morgan wrote it to express some of his views as a philosopher, logician, and mathematician. I see it as an exaggeration of actual systems in nature, where no living thing exists independently of everything else.
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The two-horned oak leaf gall wasp — Dryocosmus dubiosus — wreaked havoc on live oaks in 2023. It will surely come again, but probably not every year at the same level of infestation. Why? Because environmental conditions favoring it change from year to year, and though its larvae feed in oak leaf galls, other insects feed on them and the galls they inhabit.
The insect in the photo sent to me was found inside an oak leaf gall and thought to be of the adult leaf gall wasp. After some online searching, and noting some anatomical differences, I think it could be the parasitic wasp, mentioned in the literature: Torymus fullawayi (Huber) that feeds on the gall wasp.
Little wasps have smaller wasps upon their backs to bite’ em!
I could be wrong about the identification, but the principle is documented in the literature.
When certain species of eucalyptus began to die off in the late 1980’s it was discovered that a ‘longhorned borer’ beetle had made its way to California, probably via infested wooden shipping pallets and its hatchlings quickly flew off and found safe homes in local eucalyptus. The die-off was alarming. The question that arose was: Why is this so bad here but not in Australia or Tasmania, the homes of so many eucalyptus species?
Entomologists from UC Riverside investigated and determined that an egg parasitoid — a tiny wasp that lays its eggs inside the eggs of the borer and keeps the borers in check — did not arrive in California along with the longhorned beetle. As one of the entomologists said, the beetle without its natural parasitoid had a free ticket to Disneyland.
Subsequently, Professors Jocelyn Millar and Timothy Paine developed a trial project to import the parasitoid and provide it with borer infested fresh cut eucalyptus logs. The project successfully demonstrated the effectiveness of the concept. Not only that, but the parasitoids quickly spread to nearby sites. The first longhorn borer, Phoracantha semipunctata, met its natural enemy, but another longhorn borer arrived later. That story is not over.
Big Euc pests have smaller pests upon their backs to bite ‘em… !
The principle was also demonstrated when the ash whitefly became a devastating pest in the 1980’s. It infested various tree and plant species, causing millions of dollars of damage in the nursery industry and fouling public areas with clouds of whiteflies and their sticky honeydew coating surfaces.
The ash whitefly arrived here from its homeland in the Middle East and Mediterranean without its natural companion, Encarsia inaron, another parasitic wasp. Entomologists at UC Riverside imported and released E. inaron and soon after the release, there was a dramatic crash in the ash whitefly population. It all but disappeared, in a classic success of assisted bio-control of a devastating pest.
These efforts are not done willy-nilly. Moving insects or diseases across oceans is risky. The intended predator or parasitoid might be happy to attack insects we value as beneficials, so entomologists working on these problems do their best to study potential unintended consequences.
Bill Pramuk is an ASCA registered consulting arborist and an ISA certified arborist. Visit his website, www.billpramuk.com, email questions to info@billpramuk.com, or call him at 707-363-0114.