Abstract
Quadrastichus erythrinae Kim, 2004 (Hymenoptera: Eulophidae) is known in tropical and subtropical regions to cause serious damage to various species of Erythrina (Fabaceae) by inducing stem, petiole, and leaf galls. In Japan, the existence of galls on Erythrina variegata Linnaeus was first recorded in Okinawa Prefecture in 2005, but galls were not found in that year on Amami Island, Kagoshima Prefecture. In our field survey from December 2006 to February 2007, we found that 65 (16.8%) of 323 trees of E. variegata bore galls on Amami Island and 118 (85.5%) of 138 trees of E. variegata and E. crista-galli Linnaeus on Tokunoshima Island, which is located about 49 km south of Amami Island. Because Erythrina trees were more heavily damaged on Tokunoshima Island, Q. erythrinae seems to have invaded the island earlier than Amami Island. In addition to possible multiple invasions, Q. erythrinae may have spread quickly through both islands by low-density dispersal. Up to 2007, no galls had been found on Kikai Island located east of Amami Island.
