In 2012 I first ran across some banana-shaped objects growing on Euphorbia polycarpa plants:

I vouchered the plant material and dissected some of the objects finding only tiny orange larvae which I could not identify. I have occasionally seen the galls since, but this year they have been produced in great numbers, with thousands of them felicitously placed within a few feet of my back porch. Spot-checks in other locations and another observation suggest this has been a particularly good year for the insects involved.

Euphorbia polycarpa is a member of the Euphorbiaceae. The floral structure of euphorbs is unique to the family. A cuplike involucre holds a single stalked female flower at its center, surrounded by one to dozens of male flowers. Male flowers are reduced to just a stalk with paired anthers at the ends. This arrangement is called a cyathium:

The galls are induced in the cyathium of the plant by the act of the galling insect laying its egg. The cyathium itself grows abnormally; glands and appendages normally produced on the rim of the cyathium can be seen at the apex of some galls. The walls of the gall encapsulate the egg, larva, and pupa. The distal end of the gall is open.

Thus began a hunt for the inducer. In near-daily safaris among a dozen or twenty galls at a time, I found almost nothing beyond those familiar orange larvae. The larvae were usually single, but there were multiples in a few, as many as four in a single gall. The larvae were all identical, at least to my untrained eye. Along with near-daily harvests, I placed some material with galls in petri dishes hoping for adults to emerge. Eventually some pupae turned up (images are linked to the observations):

At least two adults were found firmly ensconced in galls, one alive and one not:

All four had the head to the distal end of the gall. Note the ovipositors on the dead adult and pupae. Given the length of the ovipositors, this taxon could be a parasitoid - a parasite on a parasite. With the open end of the gall, they would not even need to perforate the gall wall.

The pupa at right above produced this adult:

All adults are similar, but not identical. Body length of all is similar, just above 2 mm. Some variations:

Female, dorsal view

Male [?] with feathery antennae

The above were found in the galls or resemble those that were. Whether they represent more than one taxon I don't know. I've been sticking with Chalcidoidea, and even that may be wrong with some of them; I'm out of my depth.

Some other wasp or wasp-like insects turned up in the petri dishes. This small wasp is very active and difficult to photograph:

It is the next most numerous wasp. Body is about 1 mm long. Began appearing later than the others, and seems to be thriving in the dishes.
ETA: This appears to be a whitefly parasitoid in the genus Eretmocerus; makes sense since whiteflies are also very common on the E. polycarpa plants. Information at the link (click on photo above).

Beyond those a couple of other wasp-like critters made brief appearances, one each:

Colorful things; possibly the same taxon. Both had bodies of about 1 mm long. Deceased at left, alive at right.

I found galls similar to the Euphorbia polycarpa galls on Euphorbia melanadenia, nearly identical except for the hairs on the outer surface of the galls. The hairs are consistent with that species' usual indument:

There are other images of similar galls on related taxa here and I know there's at least one more out there - will add if found.

I've accumulated quite a pile of adult corpses - couple of dozen so far - if anyone is interested and able to attempt to further ID these critters. There are also links to other observations I made in the hunt here, compiled by the ever-helpful Nathan Taylor, creator of this relevant project.

Bottom line: I have no idea which, if any, of these wasps are inducing the galls.

Posted on October 18, 2022 02:36 PM by stevejones stevejones


Fascinating, Steve! Thanks!

Posted by rangermicah 8 months ago (Flag)

Good stuff Steve, I'll keep an eye out for these galls. Do you have any tips on rearing them?

Posted by psyllidhipster 8 months ago (Flag)

Thanks, Chris. Nope, no advice on rearing; I just put some stems with galls in petri dishes and let time do its magic. Most of the photos were taken through the plastic lids of the dishes, at least with the living insects.

Posted by stevejones 8 months ago (Flag)

Wow.. way up there on the COOL meter!!!
Kudos for your research so far. I'm eager to hear more.

Posted by ezpixels 8 months ago (Flag)

Found one more wasp.

Posted by stevejones 8 months ago (Flag)

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