Heat-Stressed Mealybugs Feed Harder, Texas A&M Data Show

Pasture mealybug has spread to 114 Texas counties since its first confirmed sighting in July 2025, and Texas A&M AgriLife Research scientists now have early evidence that heat stress makes the insect feed more destructively. The finding carries direct weight for the state's $15.5 billion cattle industry, which depends on the forage and grazing land the pest attacks.

Doctoral student Ashley Zavala leads the study in the lab of Thomas Chappell, an epidemiologist in the Texas A&M Department of Plant Pathology and Microbiology. The work measures mealybug feeding behavior across a range of environmental conditions. It aims to explain a pattern ranchers already know: some infestations devastate fields while others do far less harm.

Why heat changes the damage equation

The insect feeds by piercing plants and drawing out fluids — sugar-rich phloem sap typically, though it can also tap the xylem, the water-carrying tissue. Rising temperatures push the insect toward more xylem feeding to stay hydrated, Chappell said.

The more consequential shift involves saliva. Heat increased how often the mealybugs salivated into the phloem, and saliva carries the enzymes and toxins that damage plants. Hot conditions could therefore mean more harm from the same number of insects — a margin question for forage producers, since equivalent pest pressure under a cool spring and a hot summer may no longer mean equivalent losses.

In severe infestations, fields turn brown, thin out dramatically or die entirely, a condition known as pasture dieback. The pest affects a broad mix of native and improved warm-season grasses, from bermudagrass and bahiagrasses to bluestems and other key forage species. It has also been reported in Florida, Georgia and Louisiana, and scientists are concerned it could reach sugarcane and rice production.

How do you measure an insect's bite?

The team uses electropenetrography, or EPG. The method attaches a sensor to the insect and the plant and records feeding activity as a waveform, which Chappell compared to reading an electrocardiogram. The researchers want to pinpoint the temperature range where feeding and the excretion of toxic saliva increase and damage plants.

"It's tedious work, but it's exciting to know that what we are learning could make an impact and help people deal with this serious pest threat," Zavala said. "If we can better understand what changes the way these insects feed, that's a piece of the puzzle that can help guide management."

Chappell's lab is applying EPG to a related mealybug species on pepper plants, but he sees a direct line to the pasture pest. Forecasting tools that weigh feeding behavior, plant stress and susceptibility, and weather patterns could let growers time pesticide applications more precisely — the same approach weather-driven modeling already provides for other pests. Intelligent agriculture systems, he added, could sharpen both the data processing and the accuracy of those forecasting tools.

"Mealybugs were relatively underexplored because before pasture mealybugs, they had not been as big a threat to ag producers," Chappell said. "EPG paves the way for new insights about pest-plant interactions in specific environmental factors."

What does this change for ranchers?

Not management guidance yet — these are early findings, not harvested results. But AgriLife Research and AgriLife Extension scientists across multiple departments are collaborating on the pest from every angle. They have already linked population growth to canopy density, heat, humidity and rainfall, and they continue to study forage plant susceptibility and recovery. The goal is a suite of science-based management tools producers can depend on.

"Texas A&M AgriLife entomologists are tracking where pasture mealybug is, how populations move and how to control it, and forage researchers are examining which forage varieties hold up better under their stress," Chappell said. "Ashley's work connects these by demonstrating how weather affects feeding intensity."

Institutionally, the effort has structure behind it. Texas A&M AgriLife formed the Emerging Pest Task Force of subject matter experts to respond to agricultural and natural resource threats from pest incursions. Pasture mealybug is the task force's current priority, and it recently testified before Texas Legislature members in Austin on New World screwworm and pasture mealybug. A round of AgriLife Research seed grants to several departments in the College of Agriculture and Life Sciences will fund additional projects on the pest, with Zavala's feeding-behavior data now adding a weather-driven layer to the risk map ranchers will eventually use.