Leaf age and larval performance of the leaf beetle Paropsis atomaria.
Larval performance of the chrysomelid Paropsis atomaria was determined for larvae reared on both new and mature leaves of Eucalyptus blakelyi in field tests in Canberra, Australia, in 1986. Larvae were transferred to mature leaves at different ages; control larvae stayed on new leaves throughout all instars. Only larvae that were reared on new leaves during the third instar survived to pupate on mature leaves; development 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. Low survival and slow development on mature leaves were mainly due to failure by larvae to feed. Larvae palpated leaves and could discriminate among leaf ages immediately, without biting into the leaf tissue. New leaves had higher concentrations of oil and tannins than old ones, but there were no significant differences in nitrogen concentrations in the 2 types of leaves. Mature leaves were more than 3 times as tough as new leaves, in terms of penetrometer force. In drought years, E. blakelyi may not produce sufficient new leaves to supply specialist herbivores with their preferred food resource. It is inferred that drought years reduce P. atomaria larval performance significantly and thus influence the population dynamics of the insect.