Wednesday, January 31, 2024

Hibiscus Scentless Plant Bug Life Cycle

It is a rare occasion when I am able to document all life stages of an insect species, let alone in the same location, or over a period of a couple of days. That is what happened, though, when I photographed a population of a scentless plant bug, Niesthrea louisianica, sometimes called the Hibiscus Scentless Plant Bug. Indeed, hibiscus and related plants in the family Malvaceae are their hosts. Our saga takes place in Okawville, Illinois, USA, in October of 2023.

While exploring the yard at my sister-in-law's home, I happened to notice adults and nymphs of this insect on buds of what I learned later was the plant known as Rose-of-Sharon, Hibiscus syriacus. Even the adults are not very large, measuring only 6.5-8.5 millimeters in body length. They are noticeable because they are so brilliantly colored in orange and red, with legs annulated (banded) in black and white. Niesthrea louisianica is a mostly southern U.S. species, but ranges from New York to Florida, and west to Iowa, Texas, Arizona, Utah, and California.

Apparently it is not unusual to find all stages in the life cycle at the end of the plant's growing season, and the adult insects overwinter anyway. Females can live about two months, males roughly fifty days. There can be at least three or four generations per year in southern latitudes, fewer farther north. Females deposit eggs in small batches, up to 36 in number, on the underside of leaves, beneath the bracts of the flower buds, or on the seed heads. One female can lay up to seven hundred eggs in her lifetime. I spotted a couple of egg clusters, one being guarded, presumably by the female that laid them.

The first instar nymphs that emerge from the eggs are so tiny! This species goes through five instars, an instar being the interval between molts. Like all true bugs, metamorphosis is "simple," each instar incrementally larger than the last, with the final molt to adulthood resulting, in this case, in a winged, sexually-mature individual. All life stages feed on the flower buds and seeds of the host plant, inserting the stylets of their rostrum to reach the interior fluids and tissues.

The activity period of the Hibiscus Scentless Plant Bug differs with latitude, but the life cycle begins in April or May, when the overwintered females lay eggs. It concludes with the end of the growing season, in October or even later.

One interesting aspect of Niesthrea louisianica is its potential role in controlling a problematic plant called Velvetleaf, Abutilon theophrasti. The bugs can carry pathogenic fungi in the genera Fusarium and Alternaria, which ride on the insects and infect the seeds of the plant, weakened from the feeding activities of the insect.

The "scentless plant bug" moniker may not apply in the case of the Hibiscus Scentless Plant Bug. They possess metathoracic glands, and a single dorsal abdominal gland, that produce copious amounts of exocrine chemicals for self-defense. Not that this deters spiders, one of their chief enemies, nor does it prevent parasitoid tachind flies, genus Leucostoma, from attacking the adult bugs. Scelionid wasps, genus Telenomus, exact a toll as parasitoids of the bug's eggs.

This is one of those species that fits the entomological addage of "Once you see one, you will see them everywhere." They are "locally abundant," like many host-specific phytophagous (plant-feeding) insects. They will not be on every plant because the defensive chemicals of the host plant vary from one individual plant to the next. Be on the lookout for them in Ohio, Indiana, and northern states currently out of their accepted range. Climate change may be driving a northerly range expansion.

A pair of less colorful specimens from Cape May, New Jersey, September, 2017

Sources:Baker, James. 2016. "Hibiscus Scentless Plant Bug," NC State Extension Publications
Kremer, Robert J. 1992. "Integration of a Seed-feeding Insect and Fungi for Management of Velvetleaf (Abutilon theophrasti) Seed Production," Proceedings of the Eighth Annual Symposium on Biological Control of Weeds.
Jones, Walker A., H.E. Walker, P.C. Quimby, and J.D. Ouzts. 1985. "Biology of Niesthrea louisianica (Hemiptera: Rhopalidae) on Selected Plants, and its Potential for Biocontrol of Velvetleaf Abutilon theophrasti (Malvaceae)," Annals of the Entomological Society of America 78(3): 326-330.
Slater, J.A., and R.M. Baranowski.1978. How to Know the True Bugs. Dubuque, Iowa: Wm. C. Brown Company Publishers. 256 pp.
Moorehouse, Angella. 2023. Flower Bugs: A Guide to Flower-associated True Bugs of the Midwest. Minnetonka, Minnesota: Pollination Press, LLC. 360 pp.
Steill, Jennifer, and Jason Meyer. 2003. The Rhopalidae of Florida "Scentless Plant Bugs." Insect Classification Project. 23 pp.

A group of juveniles on an unidentified host plant, New Jersey

Sunday, January 7, 2024

Book Review: Underbug

Termites exist at the intersection of biology, chemistry, ecology, engineering, and perhaps even philosophy. In Underbug: An Obsessive Tale of Termites and Technology, author Lisa Margonelli masterfully weaves all of these elements together, and then some. She manages to remain in that sweet spot between total participation in the story, and complete detachment, never overtaking the spotlight of her subjects, both insectian and human, but still revealing the personal impacts of where her investigations took her. She maintains empathy with the reader while taking them on a globe-trotting journey.

Underbug has more to say about humanity than you would expect in a book ostensibly about insects, let alone insects we consider economic pests. This is about where curiosity and imagination can take you. It ventures from the microscopic world of termite gut fauna to the megascopic, landscape-writing engineering of millions of diminutive members of a termite colony. How are they so successful? How can we harness their power to digest cellulose and use it to manufacture “grassoline?” What lessons exist for how to reclaim an abandoned mine and turn it back to its native grandeur?

It may be cliché to say that a book has something for everyone, but this one truly does, provided you are prone to a fascination with science, or relish contemplating the planet and our own place on it.

The book is divided into six parts, each one set off by a black-and-white illustration that gives the impression, appropriately, of a woodcut print (they are linoleum block prints by Thomas Shahan). The dust jacket has intentional holes in it, as if the book has already been “digested” by its very subject. How perfect. Margonelli manages to have a reverence for both termites and science, but never comes off as preaching or dogmatic. There is humor here and there, and the prose are descriptive enough to put you right in the center of things.

As a failed academic myself, I felt overwhelmed occasionally by the mathematics, genetics, and technological aspects of the stories (there are several), but remained captivated by the human characters and, of course, the mysteries of the insects.

Margonelli ultimately questions the accepted scientific course of the abstraction of natural processes, whether it has its limits, or if it is even a potential failing of our own species. Are we too attached to the idea that every other species, every habitat, serve us first, to justify its existence?

Without giving too much away, the conclusions reached are, as one might expect, inconclusive; for termites exist at the intersection of the known, the unknown, and the unknowable. Sometimes the biggest question for a researcher or engineer is when to give up.

Underbug was published in 2018, by Scientific American / Farrar, Straus and Giroux, New York. It is 303 pages, including notes and index. This is as much an adventure book as it is a revealing glimpse into what defines science in the twenty-first century. Highly recommended.