[Creatonotos gangis] [a]dult males secrete the pheromone hydroxydanaidal in order to attract mates. The amount produced, and the size of the coremata (scent organs) which produce it, are however dependent on the diet that the moth experienced as a caterpillar.

If the larval diet contained pyrrolizidine alkaloids, then the coremata become large and the male will release up to 400 miligrams(0.4 grams) of hydroxydanaidal, but if it does not, then the coremata do not grow large and no scent is produced.

Photograph by Juan Manuel.
Quoted text via Wikipedia.