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When a Native Species Becomes Invasive
University of Florida Research on Gloomy Scale Insects


Gloomy scale insects are found throughout the southeastern United States, from Maryland to Florida to Texas. They are primarily found on red maple trees but will feed on other species as well, including silver maple trees.
Credit: Lorraine Graney, Bartlett Tree Experts,, CC BY-NC 3.0, via

The gloomy scale insect, Melanaspis tenebricosa, was found to reproduce more when the red maple trees they live on are stressed by heat and drought, according to a study by University of Florida assistant professor Adam Dale.

The research was conducted when Dale was a doctoral student at North Carolina State University in 2014 and 2015. He and a team of researchers looked at insect populations on urban red maple trees throughout Raleigh, N.C., half of which were irrigated twice a week during the summers.

At the end of 2015, gloomy scales were collected from the trees for dissection. The insect's body size was measured, and the number of eggs produced was counted. The researchers then looked at how these numbers related to the temperature in the tree's canopy and its irrigation status.

The researchers found that the insect was more prolific on hot and dry trees than cool, irrigated trees. It is more abundant on urban trees than rural trees, and so reduces the health of the urban trees.

When it severely damages the urban trees, the native species acts more like an invasive pest.

To prevent problems, Dale recommends selecting trees other than the red maple to plant in areas where heat and drought stress are likely. Existing trees should be irrigated more during warmer months to reduce drought stress and manage the gloomy scale insect.

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August 20, 2019, 8:54 pm PDT

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