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

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