Many insects react rapidly to environmental change. Particularly, ensembles of closely interacting species are most vulnerable to change because survival depends on the persistence of multiple group members. Thus, myrmecophiles butterflies are often declining. A lycaenid butterfly Niphanda fusca depends on aphids during their earlier larval periods and on an ant Camponotus japonicus during their later larval periods. N. fusca used to distribute universally in Japan mainland. However, the butterfly is rapidly declining in various regions, and is treated as an endangered species.

To obtain basic information for their conservation, we visited their habitats in Japan. In most cases, N. fusca inhabits secondary grasslands. However, in central Japan, they also inhabit natural semi-bare land, such as cliffs. To clarify whether populations in these two kinds of habitat have different origins, we sequenced 620 bp of a mitochondrial ND5 gene of N. fusca collected over Japan. Most populations have only one haplotype, suggesting that genetic diversity had been lost. Geographical distance rather than habitat type can better explain the haplotype distribution, indicating that populations in different habitats did not have different origins. We will analyze phylogeny of C. japonicus to test whether the lineage of the host ant affect those of N. fusca.