- The Alcon Blue Maculinea alcon and the Mountain Alcon Blue Maculinea ‘rebeli’ are obligate ant-parasitic butterflies with no distinct morphological and genetic differences but clear ecological separation.
- The two butterflies generally lay their eggs on distinct host plant species: M. alcon on Gentiana pneumonanthe and M. ‘rebeli’ on Gentiana cruciata. The egg-laying behaviour of these two ecotypes has previously only been investigated in sympatric, but not in syntopic populations. We studied the egg-laying preferences of M. alcon and M. ‘rebeli’ in a unique area where they co-occur, and where they use different host plants.
- The distance to the nearest other host plant does not seem to influence the decision of female butterflies as to whether to lay eggs on a specific host plant.
- The two butterflies laid their eggs on different parts of their host plants: M. alcon preferred the sepals of G. pneumonanthe flower buds, while M. ‘rebeli’ laid most eggs on the leaves of G. cruciata.
- The major factor correlated with the number of eggs laid on the host plant seemed to be plant quality (number of flowers, stem length, etc.) for both butterflies.
- The present study reveals behavioural differences between the two Alcon Blue forms under unique syntopic conditions, a hidden intraspecific diversity that is worth conserving.