Effects of construction work on crane flies (Diptera: Tipulidae) in the middle reaches of the River Shinano in Central Japan

Abstract

A large bank-protection works project undertaken during winter (from late October 2001, to late March 2002) in the middle reaches of the River Shinano, Japan's longest river, drastically altered the riverbed structure. To assess the effect of the project on the river's crane flies, we collected larvae and pupae with a Surber sampler in the construction area and in a control area from April to June, 2002. We also collected crane fly adults with light traps around the construction area from April to July of 2000, 2001 and 2002, as background information for the effects portion of this study. As a result, we described a total of 31 newly recorded crane fly species in the middle reaches of the River Shinano. In all three years of study, the sex ratio for all taxa combined was 74.8 to 75.5 percent males. Antocha was the dominant taxon, Antocha (Antocha) bifida was the dominant species, and its abundance did not differ significantly among years. The age structure of the Antocha bifida larval population changed in the construction area following construction, but not in the control area. Our data suggest that the bank-protection project significantly affected the Antocha bifida larval population in the study area.