University of Kentucky study finds insecticides struggle to control cockroach populations

New research from the University of Kentucky suggests that common household insecticides may be ineffective at controlling large populations of German cockroaches. While commercial essential oil-based products showed high immediate mortality rates—killing over 96 percent of cockroaches when sprayed directly—the long-term impact on hidden populations is minimal.

Researchers found that German cockroaches typically reside in narrow crevices, such as behind refrigerators, inside walls, and within cabinets, making them difficult to reach. Zachary DeVries, an associate professor of entomology at the University of Kentucky, noted that killing a single visible insect does little to address the dozens of others hiding nearby.

Senior researcher Daniela Jackson explained that while the products appear effective in the moment, their efficacy drops significantly once the solutions dry. The study tested how long residues remained active on surfaces like ceramic tile and pine wood, finding that the ability of hidden insects to control a population depends on the persistence of the toxin after application.