Differences in oviposition strategies between two ecotypes of the endangered myrmecophilous butterfly Maculinea alcon (Lepidoptera: Lycaenidae) under unique syntopic conditions

The Alcon Blue Maculinea alcon and the Mountain Alcon Blue Maculinea 'rebeli' are obligate ant-parasitic butterflies with no distinct morpho- logical and genetic differences but clear ecological separation. 2. The two butterflies generally lay their eggs on distinct host plant species: M. alcon on Gentiana pneumonanthe and M. 'rebeli 'o nGentiana cruciata. The egg-laying behaviour of these two ecotypes has previously only been investi- gated 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. 3. 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. 4. 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. 5. 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. 6. The present study reveals behavioural differences between the two Alcon Blue forms under unique syntopic conditions, a hidden intraspecific diversity that is worth conserving.