Buttonbush (Cephalanthus occidentalis, family Rubiaceae) is one of my favorite native woody shrubs. It is highly tolerant of poorly drained soils and is commonly found in Ohio, thriving in wetlands and at the edge of ponds. However, it does not do well at the dry end of the soil moisture spectrum.
The shrubs sport large, dark green, glossy leaves. The button-like name-sake flowers are highly attractive to pollinators, although their passing resemblance to the SARS-CoV-2 virus is a bit disconcerting.
Buttonbush is relatively free of pests. Members of the genus Cephalanthus use an array of secondary plant metabolites for plant defense, including alkaloids, terpenes, and phenolic compounds. It’s a family business with members of the Rubiaceae family producing well-known alkaloids like antimalarial quinine produced by Cinchona trees (Cinchona spp.), and caffeine produced by coffee plants (Coffee spp.). It’s an eye-opener.
However, deploying chemical defenses against herbivory is a two-edged sword for plants. What happens if natural selection imbues an herbivore with the ability to handle the chemical defense? Not only is the plant no longer protected from the herbivore, but the plant’s chemical defense also drives away the competition. The herbivore gains a competitive advantage by becoming a specialist on its plant mate.
On the other hand, specializing in feeding on a single plant species is a two-edged sword for an herbivore. The loss of its host dooms the herbivore. One of the best examples is the Karner Blue butterfly (Lycaeides melissa samuelis) and its complete dependence on the Wild Blue Lupine (Lupinus perennis). In a twist on the Monty Python quote, “Your life or your lupines!”, the butterfly is endangered owing to the loss of habitat supporting the lupine.
Of course, evolution never sleeps. The Monarch Butterfly (Danaus plexippus) has become the poster child for [fill in this blank]. However, at the root of the monarch tale is its storied ability to handle the steroidal cardenolides found in the sap of Milkweeds (Asclepias spp.). What’s good for the monarch is also good for the commoner. Natural selection has gifted a plethora of other insects with the ability to utilize milkweeds, sometimes at the expense of the monarch.
Buttonbush Specialists
Tenthredinid Sawflies
In early June, a sawfly, Pseudosiobla excavata (family Tenthredinidae), was discovered feeding on containerized buttonbush in a hoop house at the Cincinnati Zoo and Botanical Garden’s Bowyer Farm in Warren County. This is a buttonbush specialist. No larvae were found feeding on any other plant species in the diverse collection of plants on the Farm.
Ohio is also home to another sawfly that’s a buttonbush specialist, P. cephalanthi. However, it’s much less common in our state compared to P. excavata.
Both of the buttonbush specialist sawflies have one generation per season. They spend the winter in the soil in cocoons constructed of soil particles cemented together. Adults emerge in the spring to deposit eggs on their buttonbush host and the larvae feed until mid-summer when they drop to the soil to construct overwintering cocoons.
P. excavata larvae are covered in a powdery material (“bloom”). Consequently, they vary in their coloration based on the accumulation of the bloom.
On a side note, sawfly larvae strongly resemble caterpillars. Of course, sawflies belong to the order Hymenoptera and are related to bees and wasps. Caterpillars are the larvae of moths or butterflies, which belong to the order Lepidoptera. The similar appearances can present a challenge in identifying a leaf-eating culprit.
A handy way to distinguish sawfly larvae from caterpillars, and vice versa, is to count the number of prolegs. The images below show the different types of legs found on sawfly larvae and caterpillars. Caterpillars have 5 or fewer pairs of abdominal prolegs. Sawfly larvae have 6 or more pairs of abdominal prolegs.
Here's a handy way to remember this: Caterpillars have the same number or fewer pairs of abdominal prolegs as the fingers on your hand; sawfly larvae have more pairs of abdominal prolegs than the fingers on your hand.
Buttonbush Shoot Borer / Leafmining Moth
Two moths belonging to the genus Mompha (family Momphidae) are also buttonbush specialists. They are M. cephalanthiella, which is commonly referred to as the Buttonbush Leafminer Moth, and M. solomoni, which was described in 2004 and has not yet acquired a popular name. However, for reasons that will become apparent, I’m going to refer to it as the Buttonbush Shoot Borer / Leafmining Moth. These and other small moths are called “microlepidoptera,” which is not a taxonomic group but a nod to their diminutive size.
I have never found the buttonbush leafminer moth in southwest Ohio, so I have no pictures. However, it is reported to occur in our state. The caterpillars are described as producing blotch mines that extend along the leaf margin and are free of excrement (frass).
I observed the handiwork of the Buttonbush Shoot Borer / Leafmining Moth last week in a local county park. It has one of the most peculiar life cycles for a leafminer that I’ve ever come across.
There are three generations per season, with the first generation having a distinctly different lifestyle compared to the second and third generations. First-generation caterpillars bore into the developing shoots in the spring. Their damage causes the new shoots to wilt, die, and turn black. It can easily be mistaken for freeze or frost damage, which I did! Frankly, I didn’t realize the significance of the symptom until I learned about the life cycle in the literature.
Once the caterpillars complete their development, they emerge from the shoots to pupate in the leaf litter. Some of the second-generation moths that rise from the leaf litter will lay their eggs on the shoots. The resulting caterpillars continuing to produce the shoot-boring damage.
However, the vast majority of the moths lay eggs on leaf midveins to initiate a leafmining lifestyle practiced by second and third-generation caterpillars. The caterpillars first produce short serpentine leafmines that may lead to blotch mines. Or the caterpillars may migrate to a new location to produce another meandering leafmine that’s slightly longer.
Eventually, the caterpillars produce blotch mines. All of the leafmines are filled with frass, unlike the mines produced by the Buttonbush Leafminer Moth.
No Worries
Native herbivore specialists seldom cause serious harm to their native host. It’s simply not in their best interest. Remember, as the host goes, so goes the specialist (e.g., Karner blue butterfly).
Neither the tenthredinid sawflies nor the momphid moths have a record of causing serious harm to buttonbush. Their damage is primarily aesthetic. The yardstick we should use to measure pest impact and decide when to act is whether the pest causes significant harm to overall plant health. The damage produced by these buttonbush specialists does meet that standard.
Acknowledgment
The author thanks Charles (Charley) Eiseman, who is an author, naturalist, and entomologist extraordinaire, for confirming the identification of Pseudosiobla excavata. You can visit his website to purchase his books and subscribe to his blog at:
Selected References
Birnbaum, S. S. L., & Abbot, P. (2018). Insect adaptations toward plant toxins in milkweed–herbivores systems–a review. Entomologia Experimentalis et Applicata, 166(5), 357-366.
https://doi.org/10.1111/eea.12659
Bruzzese, D. J., Wagner, D. L., Harrison, T., Jogesh, T., Overson, R. P., Wickett, N. J., ... & Skogen, K. A. (2019). Phylogeny, host use, and diversification in the moth family Momphidae (Lepidoptera: Gelechioidea). PLoS One, 14(6), e0207833.
https://doi.org/10.1371/journal.pone.0207833
Eiseman, C. S., Smith, D. R., & Feldman, T. S. (2023). Distinguishing Larvae and Prepupae of the Two Buttonbush-Feeding Sawflies (Hymenoptera: Tenthredinidae: Pseudosiobla Ashmead). Proceedings of the Entomological Society of Washington, 125(1), 195-200.
https://doi.org/10.4289/0013-8797.125.1.195
Grundel, R., Pavlovic, N. B., & Sulzman, C. L. (1998). Habitat use by the endangered Karner blue butterfly in oak woodlands: the influence of canopy cover. Biological conservation, 85(1-2), 47-53.
https://doi.org/10.1016/S0006-3207(97)00165-1
Hall, S.P., Sullivan, J.B., Petranka, J.W., Feldman, T., George, D., … & Howard, T. (2025). The Moths of North Carolina [Internet]. Raleigh (NC): North Carolina Biodiversity Project and North Carolina State Parks.
https://auth1.dpr.ncparks.gov/moths/index.php.
Smith, D. R. (1979). Nearctic sawflies. IV. Allantinae: Adults and larvae (Hymenoptera: Tenthredinidae). Technical Bulletin, U.S. Department of Agriculture 1595: 1-172.
https://ageconsearch.umn.edu/record/157742/files/tb1595.pdf
Wagner, D. L., Adamski, D., & Brown, R. L. (2004). A new species of Mompha Hübner (Lepidoptera: Coleophoridae: Momphinae) from buttonbush (Cephalanthus occidentalis L.) with descriptions of the early stages. Proceedings of the Entomological Society of Washington, 106(1), 1-18.
