The researchers set up trials to look at how organisms learn and on what basis they choose. They manipulated the preferences of the locusts: the insects met peppermint-flavoured grass when they were hungry and lemon-flavoured grass when they were not so hungry, and later behaved as if peppermint-flavoured grass was preferable. When they reversed the treatments, the locusts reversed their preference.
Professor Alex Kacelnik in Oxford’s Zoology Department, one of the authors of the study alongside Spence Behmer and Lorena Pompilio, said: ‘This is interesting because value depends on the condition of the organism at the time it learns, and thus what the animals learn depends on their condition and not only the properties of the food. We call this learning mechanism “state-dependent valuation”.’