"What a thousand acres of Silphiums looked like when they tickled the bellies of the buffalo is a question never again to be answered, and perhaps not even asked." -Aldo Leopold
I never know when I’ll find a new nature photography project, or, more accurately, when a nature photography project will find me. In this case in the form of a hackberry (Celtis occidentalis) leaf, blown in to land on our front walk from one of this past year’s summer storms. I still have not identified a hackberry within a square block of our house, so I am still unsure from what distance this leaf came to arrive at our front steps.
A hackberry (Celtis occidentalis) leaf with galls formed by Pachypsylla celtidismamma, known generally as the hackberry nipplegall maker or hackberry psylla.
I pretty quickly identified the leaf and the responsible gall inducer. Pachypsylla celtidismamma is a plant-parasitic hemipteran in the Aphalaridae family. The Pachypsyllinae, the subfamily in which these guys are organized in, feed only on hackberry. I wasn’t sure what the fate of the gall makers might be, once the leaf was separated from the tree. I doubted that they would be able to make it to adulthood, so I thought this would be a great time to use my 2-5x macro lens.
Pachypsylla celtidismamma nymphs located within the chambers of their gall home. Two individual nymphs can be seen in this photo. An inquiline species (Pachypsylla cohabitans) can also be found within the galls but I have no idea how one would tell the difference between nymphs of these two species.
I cut open a few different galls and they all contained at least two cute nymphs. After emerging from their gall nurseries, the adults overwinter in cracks and crevices of the hackberry tree’s bark until the following spring. Females need to be present at just the right time in spring in order to insert their eggs in the developing leaves.
A Pachypsylla celtidismamma nymph removed from its gall nursery.
The presence of these galls is not detrimental to the overall health of the hackberry host. Some property owners dislike them because of the disfigured appearance of the leaves. I wish these owners could see this as being part of the overall food web in their community and a fascinating natural history story, instead of using insecticides that would affect dozens of other insect species just in the name of aesthetics.
A Pachypsylla celtidismamma nymph at approximately 1 mm in length.
Most of us are familiar with many of the parasites that infect animals, since we, as animals, are susceptible to many. Tonight I am sharing a few easily spotted and recognizable forms of parasitism in the plant kingdom. The photograph above was taken, as were all in this post, at Shaw Nature Reserve and shows a relentless parasite that can infect a number of prairie plant species. Dodder (Cuscuta sp.) is an obligate parasite, meaning it must find a specific living host plant to infect in order to survive and reproduce. One can see by the orange coloration, this plant does not contain chlorophyll and must pull the necessary nutrients from its host plant.
Silphium Wasp Gall
The next parasite is of a form that I am just beginning to study and am finding quite interesting. Plant galls are simply growths of plant tissue, formed not by the host plant, but by other organisms. The variety of gall former as well as gall formation is astounding, to put it mildly. Insects are the primary organisms that cause gall formations, but other arthropods, fungi, bacteria and viruses form galls as well. Researchers are just beginning to learn the basics behind how these parasites cause the formation of such specific, and often beautiful galls.
The particular gall that is found on this poor Rosinweed plant pictured above is caused by a Silphium Gall Wasp (Antistrophus sp.). One of the gloriously interesting facts about galls, much like other forms of parasitism, is the specificity most commonly found between host and gall former. Most often a gall former can infect only one species of plant, or sometimes a group of closely related plant taxa. Such is the evolutionary arms race between host and its necessarily specific parasite. In the case of so many prairie host and gall former relationships, the outcome is sad for both. The near elimination of this habitat has caused dramatic reductions in the variety and abundance of prairie plant species, and accordingly, has had similar effects on the insects that form galls on these plants.
Silphium Gall Wasp
Having observed these galls for so many years, I decided to cut one open to see the developments within. A single gall can host many developing was larvae. In this small section I was able to count no fewer than five wasp galleries, each harboring a developing wasp. The two examples of parasites presented above are just a small example of the number of parasitic species that the Silphium support. A number of other insects/arthropods use Silphium for food and shelter. Birds love the seed and use the plants’ long strong stems for perches. In many ways the Silphium are keystone species and can be considered as important to the prairies as trees are to the forests.
Grape Phylloxera
Grape Phylloxera is caused by an aphid-like insect and is a parasite to native grapes. In the mid-1800s this species was accidentally released in Europe and nearly destroyed the French wine industry. The life cycle of this insect and its relationship to its host is mind-boggling. As many as 18 different life stages have been identified – from sexual to asexual, winged, foliage feeding to root feeding. This complexity, as with so many other multi-stage, specific host-parasite relationships creates major problems in man’s attempt at developing commercial controls. To date, this parasite cannot be controlled with any pesticide solution; the only remedy is still resistant stock that nature has developed in this host-parasite arms race.
A Thousand Acres of Silphiums 