1978 Volume 29 Issue 2 Pages 87-91
Chemical control of Chironomid larvae was investigated in the two different rivers, Zenpukuji and Nogawa, of Tokyo. The River Zenpukuji with a moderate current was treated with temephos W. P. for 60min at 1ppm. Seven days after the treatment, larval population was reduced by 80% in the area from the treatment spot to the 500-meter point downstream, and by less than 70% at the 900-meter point downstream. However, number of the 1st-instar larvae resurged 10 days after treatment. The River Nogawa (Koganei City, Tokyo) was treated with temephos W. P. for 60min at 1ppm. Four days after the treatment, there was no larval population of midge in the area from the treated spot to the 3,100-meter point downstream, but young instar larvae resurged 8 days after the treatment. One month after the treatment, the larval population was larger than the pre-treatment period. The second test in the same river with 0.68-ppm treatment for 60min resulted in inferior control, which is considered to be attributable to the differences in chemical concentration and to the low temperature (24℃ vs. 19℃). Within several hours after the treatment, a great number of the larvae and pupae were carried away, and most of them were found dead. All the larvae intoxicated were observed to die in 72hrs under the laboratory conditions. However, some portion of the larvae which survived in mud tubes after the treatment, emerged into adults.
