FEEDING-HABITS AND CHANGE OF BODY-COMPOSITION WITH AGE IN 3 NYMPHALIDBUTTERFLY SPECIES

Three species of nymphalid butterflies with different types of adult f eeding behaviour were examined to see how the allocation of larval-der ived resources to abdomen vs thorax change with age. Adults of Pararge aegeria and Speyeria mormonia feed on poor-quality diets. They are ex pected to be more dependent on larval-derived reserves stored in the a bdomen for reproduction than are species with high-quality diets. In a ccordance with these expectations abdomen mass decreases with age in b oth males and females. Furthermore, thorax mass of females also decrea ses with age. Since the bulk of the thorax consists of flight muscles, this suggests that old females use resources derived from flight musc les for egg production. However, since thorax ratio (thorax mass/total mass) increases with age, flight properties such as speed and maneuve rability are likely to be unchanged or even improved with advancing ag e. Adults of Heliconius hecale, which feed on a more rich-quality diet , show a reversed pattern compared with the other two species. In both sexes, abdomen mass and thorax mass increase with age.