Observations on the effects of antimosquito measures in the control of filariasis in 1958

Abstract

Some basic studies were made on the methods of control mosquitoes, which are the vectors of filariasis, in the south-western areas of Japan. The problem that arose during the work and the results obtained are summarized. 1. The larvae of the four species of mosquitoes were used in the screening test of various insecticide emulsions. The species were : Culex pipiens pallens Coquillett, Aedes aegypti Linne, Aedes albopictus Skuse, Armigeres subalbatus Coquillett. Parathion was the most effective insecticide followed by dieldrin and various other organic phosphates were less effective than these two chemicals. The residual effect of each insecticide was tested on the mosquito larvae by using each insecticide in solution at its LC_<50> concentration : The chlorinated insecticides as p-p'-DDT, lindane and dieldrin were all as effective at two days after the application as at the time of application, whereas the organic phosphorus insecticides, diazinon and malathion had lost entierly their effectiveness two days later. 2. It was observed that Culex pipiens pallens rested on the dark vertical room surfaces such as walls, door and windows. Also, many dead mosquitoes were observed in the adjacent unsprayed room, to that sprayed with dieldrin. 3. The susceptibility between adults and larvae differed greatly when the insecticide was applied to the adult's dorsal thorax by topical application and to the larvae by dipping in water suspension. By the Busvine-Nash contact method 2 hours exposure to inpregnated filter papers with counting 24 hours later gave the most reliable results. 4. The residual spraying experiments were carried out in three villages, Matsu, Myozin and Futanazu, each about 3 kilometer distance from the other. 0.25% dieldrin emulsion was applied to two of the villages leaving Myozin as untreated check. 4 months after the application the susceptibility of houseflies to p-p'-DDT, lindane and dieldrin was measured by topical application. The houseflies were collected from the two sprayed villages and it was noted that their vigour was somewhat greater than those houseflies collected from the unsprayed villages. It is not clear whether this is due, in this early stage of the experiment, to insect resistance or to other factor. 5. In the Amami island experiments of a residual spraying of dieldrin on 30th June was made in Ariya, Nakakachi and Aminoko villages. Mosquitoes were almost completely eradicated for the duration of the summer. 6. In Ehime prefecture a residual dieldrin spray was applied in Futanazu and Matsu villages. The mosquitoes were successfully eradicated for the whole of the summer season. On the other hand, houseflies were controlled for about one month and then the population showed abnormal increase. 7. The similar phenomena were observed in all four villages sprayed in Amami island with DDT or dieldrin. A second spraying with the DDT or dieldrin emulsion was made in the same these villages. Dieldrin gave no control to the housefly whereas DDT controled them for about one week only. The reason for a lack of control of houseflies was not clear as housefly resistance to dieldrin was not proved. It is necessary to study further application of different insecticides used alternatively.