The Performance of Two Chewing Insects on Water-Stressed Food Plants in Relation to Changes in Their Chemical Composition.

The rate of development of caterpillars of Pieris rapae L. on rape leaves was not affected by whether their host plants were water-stressed or not, nor were weights of the pupae affected. Survival was high on unstressed plants and was not enhanced on stressed plants. Similarly, the rate of development of larvae of Paropsis atomaria Oliver and the weight of the prepupae were unaffected by stress in young shoots of red gum, Eucalyptus camaldulensis Dehnh., on which the larvae were feeding. In both species of plant, the degree of stress applied significantly increased the total nitrogen and amino content of the leaves. In the gum leaves, phenolic content varied inversely with nitrogen content: In well watered plants at temperatures below 25�C. phenolic compounds increased and nitrogenous compounds decreased in attacked leaves, compared with leaves on unattacked shoots of the same plant. No such differences were apparent when the plants were water-stressed, however, nor in watered plants at temperatures above 30�C.