InsectNet forum

Recently I reared a few specimens of Papilio demoleus libianus from early instar larvae collected from Citrus × microcarpa in my garden. They were reared concurrently and I believe they come from the same brood. I decided to set aside one of them to perform a little experiment - I fed this particular caterpillar less than the others, providing a few leaves only, and sometimes allowing the leaves in its container to run out before replenishing them. In contrast, the other caterpillars were given entire cuttings with an ample amount of leaves, which were replaced with fresh ones daily.

The caterpillar which had been provided with less food took a full day more (i.e. upwards of 24 hours) to eclose compared to the rest, and when it did, it was markedly smaller than the (only) other female. Upon measuring the mounted specimens, the difference was about 1.5 cm in terms of wingspan. I might also note that both specimens pictured were given adequate time to fully inflate their wings: I waited about 6 hours after eclosion to euthanize them, after which they were immediately mounted.

Of course, a difference of 1.5 cm is not what one might call "spectacular", nor is the revelation that giving less food to a caterpillar will (obviously) result in a smaller imago particularly groundbreaking news, but I find it nonetheless rewarding to perform such experiments and to see this causality for myself. I'll probably be attempting similar experiments with other reared specimens in the future.

It's not only the quantity of leaves, but also the quality throughout the larval stage. P. demoleus lays eggs on new shoots as the 1st instar larvae cannot bite older Citrus leaves. A good supply of fresh young leaves is important to promote full growth of the larva.

Minimal interaction time with other larvae is also important as they disturb each other if crowded, resulting in less time eating. These are not gregarious, unlike some species which are not affected by interaction with other larvae.

Adam.