Effects of Floods on the Survival and Species Component of Rhopalomyia Gall Midges (Diptera: Cecidomyiidae) Associated with Artemisia princeps (Asteraceae) Growing in a Dry Riverbed in Japan

Summary

The Kitagawa River flows through Miyazaki Prefecture, Kyushu, Japan. Its frequent floods disturb insect and plant communities in the dry riverbed. The species composition of Rhopalomyia gall midges on Artemisia princeps after the great flood in 2004 was apparently different from that at normal water level in 2001–2002. Running water with a velocity of 3.0 m/s removed A. princeps leaves at a relatively high rate when the plants had been submerged in water for more than several days. At the time of the flood, the river attained a water level of 15.7 m and the velocity of running water was about 3.4 m/s. This situation lasted for three days. Under such conditions, many A. princeps leaves were removed, together with midge galls. Submergence of galls caused the death of midge larvae and pupae, when it lasts for more than two days. The stem galler, R. struma, would have more chance to survive in the hard stem galls than the other leaf gallers under two-day submerged conditions. Besides, the stem galls would not readily detach from the plants even when they are sub-merged in the running water with a high velocity. Such differences in galling traits between the Rhopalomyia species are considered to have changed the species composition of the gall midges.