Inter- and intra-sexual variation in immune defence in the cabbage white butterfly, Pieris rapae L. (Lepidoptera: Pieridae)

1. Immune defence imposes fitness costs as well as benefits, so organisms are expected to optimise, not maximise, their immune responses. This should result in variation in immune responses under varying environmental conditions. 2. Males and females are expected to exhibit different immune responses because life-history differences between the sexes affect optimal immune response. These life-history differences should usually result in a greater female, than male, immune defence. In this study, intra- and inter-sexual variation in one component of immune defence, the encapsulation response, in cabbage white butterflies (Pieris rapae L.), was examined. 3. Encapsulation decreased with increasing age and in response to reduced diet quality. 4. Contrary to predictions, males generally had greater immune responses than females, although this pattern varied with age. 5. These patterns of inter- and intra-sexual variation in encapsulation may result from resource-based trade-offs with components of reproductive effort and/or because of sexual dimorphism in melanin-based wing patterns.