We investigate how encapsulation ability varies with adult age in overwintering and in direct-developing animals (development without diapause) of the green-veined white butterfly, Pieris napi. Encapsulation is a resource costly trait coupled to the immune system and encapsulation ability is predicted to decrease with age, since the resource pool of important nutrients generally decreases with age in nectar feeding butterflies. The results support this prediction and both sexes showed an age dependent decrease in their encapsulation ability. There were no significant differences between the sexes but direct-developing males tended to have a steeper decrease than females and we hypothesize that this could be the result of low available resources, since this generation is time and nutrient stressed.