Chemicals emitted from a wild South American potato species repels aphids because it mimics the aphids' alarm pheromone.
"A wild species of South American potato discharges a message-chemical, a pheromone, which resembles that emitted by aphids when they are under attack. So those aphids never land on it." (Attenborough 1995:68)
Book The Private Life of PlantsJanuary 22, 2017 David Attenborough