Proline and valine-cues which stimulate grasshopper herbivory during drought stress?

Insect herbivores, including members of Orthoptera and Lepidoptera, benefit from increased nitrogen in their food, particularly if it is in the form of easily digested amino acids 1,2 . I report here experimental evidence that grasshoppers detect and preferentially feed on grasses treated with the amino acids proline and valine, which commonly increase in plants under drought stress 3 . This ability may lead to insect concentrations on drought-stressed and nitrogen-enriched plants and thus exacerbate acridid population outbreaks through enhanced growth and survival.