ABSTRACT.1Larval performance of the leaf beetleParopsis atomariaOliver was determined for larvae raised on both new and mature leaves ofEucalyptus blakelyiMaiden. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves through all instars.2Only larvae reared on new leaves through the third instar survived to pupate on mature leaves; developmental time was prolonged by 20% and pupal weight was reduced by 50% in these larvae compared with larvae reared entirely on new leaves. Almost all larvae died when transferred to mature leaves as first, second or third instars.3Low survival and slow development on mature leaves was mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue.4New leaves had higher concentrations of oil and tannins than old leaves, while there were no significant differences in nitrogen concentrations in the two types of leaves. Mature leaves were more than 3 times tougher than new leaves, in terms of g mm−2of penetrometer force.5In drought yearsE. blakelyimay not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. We infer that drought years reduceP. atomarialarval performance significantly, and influence the population dynamics of the insec