Abstract. 1. The flight apparatus in butterflies as well as in other insects is costly to manufacture. Since most animals live in a world where resources are limited, trade-offs are expected and available resources must thus be allocated between flight and other functions such as reproduction.

2. To mitigate this trade-off, previous studies have shown that butterflies can break down flight muscles in the thorax as they age in order to use muscle nutrients for reproduction.

3. Although breakdown of flight muscles is expected to reduce flight ability, relative flight muscle ratio (thorax mass/body mass) in many butterfly species does not decrease with age.  Our aim in this study was to test the relationship between flight endurance and adult age in the green-veined white butterfly Pieris napi (L.). The tests were performed in the laboratory under five different temperatures.

4. The results showed that age has a significant influence on butterfly flight endurance; older butterflies showed reduced flight endurance. Male butterflies fly for a longer time than females and flight endurance increase with temperature in both sexes.