By Andi Anderson
A new study by Michigan State University provides important insight into the behavior of an invasive scale insect threatening wetland ecosystems in Louisiana’s Mississippi River Delta.
The research was led by MSU entomologist Andrea Glassmire and focuses on Nipponaclerda biwakoensis, a small insect that damages Phragmites australis, a key wetland grass in the region.
Although some subspecies of P. australis are invasive in North America, the type found in the Mississippi River Delta plays a vital role in shoreline stability and erosion control.
Dieback of this grass was first observed in 2016, closely matching the first detection of N. biwakoensis. Since then, the insect has spread rapidly into Texas, Mississippi, and Alabama.
N. biwakoensis is native to Japan, China, and Korea. The insect feeds by attaching to plant stems and leaves and sucking sap.
Its small size and waxy coating make it difficult to control. Heavy infestations can weaken plants and lead to plant death, raising concern for wetland health.
Researchers focused on the insect’s crawler stage, a brief period lasting about 72 hours when the insect can move and spread. “The crawler stage is a critical bottleneck for dispersal because many scale insects, including female Nipponaclerdia biwakoensis, become permanently immobile after this brief life stage,” Glassmire explained.
Controlled experiments showed that the upper parts of plant stems contained more nitrogen but also higher levels of defensive chemicals. Lower stem sections had fewer defenses. “Insects are generally nitrogen-limited, leading us to expect scale settlement on top portions of the stem with softer tissue and higher nitrogen availability,” said Glassmire. “Yet these tissues also contained higher concentrations of phenolic compounds, and scales predominantly settled on the lower stem, suggesting that phenolic defenses outweighed nutritional benefits.”
Field surveys confirmed these findings. Scientists found 20 times more adult scales near the base of stems and 12 times more parasitized scales in the same area. The patterns suggest natural enemies respond to scale distribution rather than controlling it.
The study shows that plant chemistry and structure strongly influence where invasive insects settle. These findings are critical for protecting the Mississippi River Delta, which provides ecosystem services valued between $12 billion and $47 billion each year.
By understanding insect behavior, researchers can support future management strategies to protect wetlands facing increasing environmental stress.
Photo Credit: istock-dusanpetkovic
Categories: Michigan, General