Chemicals emitted from a wild South American potato species repels aphids because it mimics the aphids' alarm pheromone.

References

"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 PlantsDecember 5, 2016
David Attenborough

Organism
Chilean NightshadeSolanumSpecies