After discovering that walnut twig beetles (Pityophthorus juglandis) were repelled by the sticky substance known as Tanglefoot, researchers identified the chemical ingredient apparently responsible: limonene. To test its repellency, they added it to funnel traps that would otherwise attract the beetles using their aggregation pheromone. In the closeup shown here, the large bottle contains the pheromone attractant, and the vial contains limonene, set to release into the trap at approximately 700 milligrams per day. (Photo by Jackson Audley, Ph.D.)