It’s a woman’s world

Galls of Disholcaspis quercusglobulus (round bullet gall wasp) on twig of Quercus alba (white oak).

Not all gall wasps (family Cynipidae) affect the leaves of their hosts—some instead affect the twigs. One example of such is Disholcaspis quercusglobulus (round bullet gall wasp), which forms round, detachable galls, singly or in small clusters, on the twigs of Quercus alba (white oak).

There are about a dozen other species in this genus, all of which seem to to have succeeded in eliminating the need for males (Weld 1959). All galls produce female wasps, which emerge from their galls during the fall and immediately lay eggs in twigs to begin the next year’s crop of females—no males needed. Ain’t evolution grand?!

Literature Cited

Weld, D. 1959. Cynipid Galls of the Eastern United States. Privately printed in Ann Arbor, Michigan [pdf].

©️ Ted C. MacRae 2021

A lot of gall

Walking Beau Diddley (my black lab) and blowing leaves today gave me an opportunity to glimpse into the world of leaf galls. Lots of organisms, both animal and disease, cause these bizarre structures to grow on the leaves and stems of various plants. In the case of the two shown here, they are cause by tiny wasps called cynipid gall wasps. There are thousands of different species of gall wasps, each creating their own characteristic type of gall and restricted to one or a few closely related host plants, but in each case the adult female wasp lays one or more eggs in the leaf—their “stinger” being used like a hypodermic needle to inject the eggs inside the leaf tissues (but completely unable to sting humans). When the eggs hatch, the larvae (called grubs) do not begin feeding directly on the existing leaf tissue, but instead secrete plant growth-like hormones that cause the plant to grow a specialized structure—called a gall—inside which the grub lives and feeds. It’s sort of like “Invasion of the Body Snatchers” on a micro-scale. When the grub has completed its development, it transforms into a pupa (kind of a wasp version of a butterfly chrysalis), and eventually the adult wasp emerges and chews its way out of the gall. It’s a marvelously elegant life cycle that goes unnoticed by most people.

Andricus dimorphus (clustered midrib gall wasp, family Cynipidae) on abaxial lower midrib of leaf of Quercus muhlenbergii (chinquapin oak).
Andricus pattoni (family Cynipidae) on abaxial leaf surface of Quercus stellata (post oak).

©️ Ted C. MacRae 2021

Hiking at Valley View Glades Natural Area

My good hiking/collecting buddy Rich called me yesterday and asked if I was interested in a hike. Since I am retired, and he is retired, there was nothing on either of our schedules that prevented us from doing it the very next day, so we decided to come to one of our favorite places that we haven’t been to in awhile—Valley View Glades Natural Area near Hillsboro.

Fall color beginning at Valley View Glades Natural Area.

I brought my big camera along because I figured Great Plains ladies’-tresses orchids (Spiranthes magnicamporum) would be in good bloom, and I wanted to get good closeups with a blue sky background (I was successful in that regard—photos coming soon). I also brought along my collecting pack in case we found a beetle or two, but in this regard I was only half-successful—careful examination of several ninebark (Physocarpus opulifolius intermedius) patches did not reveal any Dicerca pugionata (seen a week ago at nearby Victoria Glades), but I did find a Blackburn’s earth-boring beetle (Geotrupes blackburni) on the trail. We also found a gum bumelia (Sideroxylon lanuginosum) tree with copious amounts of frass at the base, indicating infestation by a bumelia borer (Plinthocoelium suaveolens), and I recorded the location so I could put an emergence cage at the base of the tree next season to catch the emerging adult.

One other item of botanical interest was downy goldenrod (Solidago petiolaris) growing near the margins of the dry post oak woodlands—a species I’ve not previously noticed but was able to recognize due to its combination of recurved phyllaries and moderately widened leaves without teeth (Buckley’s goldenrod, S. buckleyi, also has recurved phyllaries but wider leaves with the edges distinctly toothed).

Downy goldenrod (Solidago petiolaris).
Downy goldenrod (Solidago petiolaris).
Downy goldenrod (Solidago petiolaris).
Downy goldenrod (Solidago petiolaris).
Downy goldenrod (Solidago petiolaris).

An especially colorful gall caused by the cynipid wasp Atrusca quercuscentricola on the leaf of post oak (Quercus stellata) piqued both entomological and botanical curiosity.

Atrusca quercuscentricola gall on leaf of post oak (Quercus stellata). Note adult emergence hole in upper left of gall.
Atrusca quercuscentricola gall on leaf of post oak (Quercus stellata)—turned upside down.

Near the end of the hike, I pointed out a shortleaf pine (Pinus echinata) tree that may be the northernmost naturally-occurring shortleaf pine in the state. I am aware of some trees further north along Hwy 21 at Sunridge Tower Park and in St. Louis Co. at Rockwoods Reservation, but I believe in both of these cases they are planted.

Shortleaf pine (Pinus echinata).

©️ Ted C. MacRae 2021

“The Botanists Among Us: Host plant specialization in insects”

It’s been a busy week for me—just two days after doing a presentation on tiger beetles to the Webster Groves Nature Society’s Entomology Group, I gave a talk to the St. Louis Chapter of the Missouri Native Plant Society. As implied by the title, the talk focused on host plant specialization among insects, first covering the major groups of plant-feeding insects and the evolutionary themes involved in adaption to (and away from) plant-feeding, then moving to examples of different types of host plant specificity and highlighting some of the more interesting insects that I’ve encountered (and managed to photograph) over the years.

Like my talk two nights earlier, it was another fun and lighthearted conversation with a highly engaged crowd, and I appreciate the great interest shown by a group that is normally much more focused on plants than on insects. Once again, it was well-attended locally, but for the benefit of those who were not able to attend the meeting in person and that may be interested in this subject, I’ve prepared a PDF version* of the presentation that you can download and peruse at your convenience.

* All content is copyrighted and may not be reproduced or distributed without written consent.

© Ted C. MacRae 2019

Rush skeletonplant pea gall wasp

Lygodesmia juncea with galls of Antistrophus lygodesmiaepisum (Hymenoptera: Cynipidae) on stem.

The Loess Hills landform along the western edge of Iowa and extreme northwestern Missouri is home to a unique assemblage of plants and animals.  The majority of these are associated with loess hilltop prairies – grassland remnants that have their origins in the hypsithermal maximum of several thousand years ago and that persist as small relicts on the landform’s steep, dry, south- and west-facing slopes.  Many of the plants and animals found in these grassland remnants are more typically found further west in the Great Plains, but hang on in the Loess Hills as hypsithermal relicts.

Antistrophus lygodesmiaepisum galls on stem of Lygodesmia juncea.

One such hypsithermal relict is rush skeletonplant, Lygodesmia juncea, a wirey, leafless-looking plant in the family Asteraceae¹.  More common in the Great Plains, this plant occurs in Missouri only on these loess hilltop prairie remnants.  The first time one encounters this plant, they are left with the impression that the plant bears small, pea-like fruiting structures along the length of its stem.  These are not fruiting structures, however, but galls made by the cynipid wasp Antistrophus lygodesmiaepisum.  Although this insect does not have a common name, it is associated exclusively with L. juncea, as suggested by its specific epithet (which also alludes to the pea-like galls with the suffix -pisum), so I see no reason why this wasp cannot be called the “rush skeletonplant pea gall wasp.”  Some sources variably misspell the genus as Anistrophus (without the first “t”) or the species name as simply pisum, a synonym first introduced by Ashmead in the late 19th century a few years after the species was described (I made both mistakes [and also erroneously referred to L. juncea as skeletonweed] in one of my earliest posts: The Loess Hills in Missouri).  It would seem that Antistrophus lygodesmiaepisum is the correct name, according to Pickering (2009).

¹ Not to be confused with rush skeletonweed, Chondrilla juncea – also in the Asteraceae, which despite the similarity of common names, specific epithet, and general appearance (except with yellow flowers) is an altogether different plant that was introduced from the Mediterranean Region and is now considered an invasive weed in much of the Great Plains.

Antistrophus lygodesmiaepisum larva in gall on stem of Lygodesmia juncea.

Rush skeletonplant exudes a latex-like sap when damaged, making it unpalatable to most grazers – this latex-like sap can be seen when the galls made by the wasps are cut open.  Cynipid wasps are the second most diverse group of gall-making insects behind the gall midges, and many species are mono- or oligophagous (Ronquist and Liljeblad 2001), meaning that they are associated exclusively with a single plant species or group of closely related species.  Antistrophus lygodesmiaepisum is one such monophagous species, thus its occurrence in Missouri, like that of L. juncea, is restricted to the tiny loess hilltop prairie remnants in extreme northwestern Missouri.  In recent years, these prairie relicts have suffered heavily from conversion to agriculture, abusive grazing, and suppression of fire that has led to invasion by woody and exotic plants.  In Missouri, only about 50 acres of loess hilltop prairie remain, and only half of these are in conservation ownership, making it among the most critically imperiled of natural communities in Missouri.  While lacking the conservation charisma of L. juncea and the dozen or so other plants and vertebrates that are restricted in Missouri to these prairie remnants, A. lygodesmiaepisum nevertheless deserves equal consideration as a Missouri species of conservation concern.

I knew this would be a difficult ID Challenge and am quite impressed that at least a few people figured out at least the correct genus.  Tim Eisele scored 8 points in this challenge to not only take the win but also move way up into a 3-way tie for 4th place in the overalls.  Ben Coulter continues to be Mr. Consistency, earning 4 points for 2nd place and retaining his overall lead by an almost insurmountable margin (see what happens when you play every game!).  JasonC beat out the other contenders for the final podium spot on the basis of a bonus point, but the hot contest continues to be the battle for 2nd place overall.  Janet Creamer still holds it at 14 pts, but there is a veritable gaggle of contenders nipping at her heals – the next few challenges could be interesting.

Photo 1: Canon 100mm macro lens (ISO 100, 1/250 sec, f/2.8).
Photos 2-3: Canon MP-E 65mm 1-5X macro lens (ISO 100, 1/250 sec, f/14).
All photos: Canon 50D , Canon MT-24EX flash w/ Sto-Fen + GFPuffer diffusers. Typical post-processing (levels, minor cropping, unsharp mask).

REFERENCES:

Pickering, J.  2009.  Database of Hymenoptera in America north of Mexico. http://www.discoverlife.org/proceedings/0000/6/html/Cynipidae (accessed 20 Jan 2011).

Ronquist, F. and J. Liljeblad.  2001.  Evolution of the gall wasp-host plant association.  Evolution 55(12):2503–2522.

Copyright © Ted C. MacRae 2011