1. Plants can respond to herbivore damage with phenotypically plastic changes in quality that negatively affect herbivores and prevent subsequent attack – induced defences.
2. The present study tested whether trees respond to herbivory with localised induction, and whether life-history traits and disease resistance of an insect herbivore are altered on induced branches of the trees.
3. The influences of localised, within-branch, herbivore-induced changes in red alder trees (Alnus rubra Bong.) on fitness characteristics of western tent caterpillars (Malacosoma californicum pluviale Dyar) were evaluated. In the field, randomly selected branches of trees were infested with tent caterpillar larvae and the adjacent branches were maintained as non-infested controls. In the laboratory, larvae were fed leaves from either induced or non-induced branches through to adult emergence. A second cohort of larvae was challenged with a viral pathogen to compare their disease susceptibility on induced versus non-induced foliage.
4. Herbivore-induced, localised responses of damaged branches reduced leaf quality for growth and the fecundity of female western tent caterpillars, but not that of males. Larvae fed induced leaves had a higher survival overall and a reduced mortality due to unidentified non-viral pathogens than did their counterparts on non-induced leaves. However, there was no influence of leaf quality on baculovirus-induced mortality.
5. These findings suggest that localised induced changes in leaf quality could potentially influence populations of tent caterpillars in contradictory ways by reducing their growth rate and fecundity to a modest degree, while improving their survival and resistance to unidentified non-viral pathogens to a larger extent.