Increase In Environmental Light Conditions Boosts Massive Flights Of Aquatic Insects

Abstract:
In the middle of June, 2010, we received the following requests from the manager of a bookstore along an irrigation canal which drew water from the Chikuma River. "During the night, massive flights of aquatic insects are attracted to the lights of my shop.” The abundance of aquatic insects was monitored by a daily catch using two light traps equipped with a black light of 6W (BL lamp) and a fluorescent lamp of 6W (FL lamp) set up near the entrance of the shop, from the end of June to the beginning of July 2010 and 2011. As a result, more than 12,000 individual aquatic insects were collected by the two light traps during the investigation periods in 2010. The most abundant taxa were Trichoptera (about 50% of the overall number) followed by Chironomidae, Tipulidae, and Ephemeroptera. The same number of Trichoptera were captured by the BL and FL lamps. However, more Chironomidae and Tipulidae were captured by the BL lamp. In addition, 3 times as many Ephemeroptera were captured by FL lamp compared to BL lamp. In April, 2011, a large shopping center opened on the other side of the bookstore. After its opening, the environmental light condition greatly changed around the investigation place. As a result, the number of aquatic insects attracted to the bookstore observed a very large change in 2011. The number of aquatic insects / 9 day increased compared with 2010, especially, due to the BL lamp. In 2011, the most captured insect was Chironomidae in the bookstore, and the individual number was 12.8 times that of 2010 by BL lamp, against 1.1 times by FL lamp. The captured number of Ephemeroptera also increased to 18 times that of 2010 by BL lamp, against decreased to 0.6 times by FL lamp. As mentioned above, if the number of aquatic insects emerging from the canal was the same in 2010 and 2011, 74.6% of the aquatic insects attracted to the bookstore in 2010 moved to the new shopping center.