Limited distribution of Caenorhabditis japonica in Japan

Caenorhabditis japonica forms a species-specific and female host-biased phoretic association with the shield bug Parastrachia japonensis. To determine the distribution of C. japonica, nematodes from P. japonensis were surveyed in islands ranging from Kyushu to Okinawa of Japan. C. japonica was isolated from all 6 sampled populations of P. japonensis from Kyushu, Amami Oshima, and Tokunoshima Islands, but not from those from Okinawa Island. The limited distribution of C. japonica in these islands is suggestive of the origin of C. japonica and its limited phoretic association with P. japonensis in this region.