水質汚濁が原因と思われるアカイエカの大発生例とその防除対策

Abstract

1. In the late spring of 1968,nuisance and biting problems by an unusually great number of adult mosquitoes took place in a suburban area of Kagamigahara City, Gifu Prefecture, Central Japan. Through a request of the city authorities, a series of field investigations were made on the population dynamics of the pest mosquitoes. Chemical and environmental control measures were also planned. 2. A pool which was receiving most of the raw wastes of a starch and woolen factories was found to be the main breeding source of the bothering mosquitoes. This pool was located at the river beach neighboring the residential quarter and had an extent of approximately 80 ares and an average depth of 0.2 meters. Population density of mosquito larvae and pupae at the station P selected in the pool was estimated by the removal method, and age structure of these aquatic stages was also analyzed. Imaginal population size in the residential district about 200 meters apart from the breeding source was estimated with light trap collections. These investigations were continued on the weekly basis during the period from June to November, 1968. 3. As the results, it was known that the overall species composition of mosquitoes of this area was very unusual for such a typical suburban habitat surrounded by many paddy fields; more than 90 percent of the collected adults and larvae were the house mosquitoes, Culex pipiens pallens Coquillett. This uncommonness was further ascertained by the comparison with the results of our mosquito surveys simultaneously performed in other two areas with similar topographical features. For the correct identification of the species, examinations were made of ommatidial number in females as well as DV/D value in males randomly sampled from the above "C. pipiens pallens" population. The results revealed that the autogenous house mosquito, C. pipiens molestus, was not intermixed. 4. Population dynamics of the C. pipiens pallens was studied by analyzing the seasonal change of larval population size and age structure. It was presumed that the adults had four definite peaks of emergence in late June, mid and late July, and early August on the bases of precursory ageing in the larval population. The actual number of adults collected by light traps and the above presumption were proven to be in good agreement. 5. Details of the control measures taken to cope with the outbreak were described, and several problems in the planning of insecticide application along with the merit and demerit of the environmental control of the pest mosquitoes, particularly of the construction of drainages, were discussed in relation to the pollution of inland water.