Sugarcane aphids are tiny bugs causing a big problem for South Plains farmers. And they’ve quickly multiplied in more than a few fields area-wide, according to the Lubbock Avalanche-Journal.

The aphid crossed from its namesake host crop—sugarcane—to sorghum, but entomologists aren’t sure why.

“There’s been some kind of shift in host preference—we don’t know why—where they prefer sorghum,” said Pat Porter, an entomologist for Texas A&M AgriLife.

Because their populations grow so quickly, Porter recommends frequent checks to detect the aphids. And when they reach a threshold of about 50-125 aphids per leaf, he recommends applying insecticide.