This field experiment examined whether early—season damage to a wild, native shrub affected the survival and cumulative numbers over several generations of its most abundant herbivore, Bucculatrix thurberiella. The effects of reduced plant density on these herbivores and possible interactions between density and induced resistance were also considered. Half of the plants were damaged experimentally at the start of the season by feeding caterpillars; the other half served as controls. Half of the plants experienced experimentally reduced densities of neighbors, while the other half were surrounded by natural densities. Early—season damage did not influence the initiation of new mines, although plants experiencing reduced density received significantly more mines than controls. Miners were less likely to survive on plants that had been damaged in 1989. This was also true in 1990 but only for those plants at reduced density. Effects on one stage in the life cycle of an insect need not translate into similar effects on the size of its population on a host plant. In this study, I was able to measure effects of resistance induction on the cumulative numbers of B. thurberiella because it completes many generations in each season and because a record of each individual is preserved at the end of the season. Damaged plants and those that had natural densities of neighbors had fewer cumulative numbers of mines than plants that had not been previously damaged and those with reduced densities of neighbors. Plant density had a greater effect than induced resistance on the cumulative number of mines produced over an entire season.