Six species of Banksia (Proteaceae) were examined at two study sites near Perth for insect larvae that destroy flowers and seed. All species, B. attenuata, B grandis, B. ilicifolia, B. littoralis, B. menziesii and B. telmatiaea, showed some damage to the conflorescence (flowering spike) while all except B, grandis and B. ilicifolia had damage to the infructescence (fruit). Six lepidopteran larvae and a curculionid larva damaged conflorescences, and five lepidopteran larvae and three curculionid larvae consumed seed. The insects were found only on Banksia and were mostly host-specific. The insects prevent about one-third of conflorescences from developing seed, but only one-third of the total conflorescences develop into infructescences. It is not known why the remaining one-third of conflorescences do not set seed. Insects destroy up to 60% of the follicles, which contain one or two seeds, on these infructescences. Examples of possible adaptations of the conflorescence and infructescence for avoiding this insect damage are suggested.