A bacterial protein called Bt toxin makes a safe and effective pesticide. But Bt-proof bugs could render the agricultural resource useless. So researchers at North Carolina State University are helping to develop a test kit that gives farmers early warning of Bt resistance, allowing them to give the affected area a break from Bt before a “super pest” emerges.

NC State entomologist R. Michael Roe calls the testing technique “embarrassingly simple” -a farmer merely adds water and a bit of Bt to wells in a cellular-phone-sized container, then drops in a few bugs from the field. Each well holds insect food mixed with an indicator dye that turns bug feces blue. Bt-susceptible pests sickened by the toxin don’t eat-and therefore don’t defecate. But resistant bugs produce blue droppings-a quick, colorful warning for the farmer, who would otherwise have to wait a week or so for the insects to die. A large-scale field study of the test kit, sponsored by Cotton Inc., should be completed this spring.