Studies on the population dynamics of mosquito larvae in a paddy field, with the special reference of the relation between rice plant farming and breeding of mosquito larva

Abstract

In order to obtain basic data for paddy-field mosquito control, a survey of the mosquito population and its fluctuation was carried out during the season of 1962, at a paddy-field in the suburbs of Kawasaki. The mosquitoes collected through the survey consist of nine species belonging four genera. Culex tritaeniorhynchus and Anopheles sinensis occupied the majority of the specimens collected from the paddy-field, whereas, Culex hayashii was a dominant species in the irrigation ditch. During the period of the rice nursery, the breeding of mosquito larvae was not abundant yet, because of the area covered by water is restricted and the season is too early. After the riceplanttransplantation (June 11-17th), C. tritaeniorhynchus and A. sinensis increased remarkably. They were, however, entirely eradicated on July 14th by the parathion spray which was made for the rice stem borer control. The population density of mosquitoes almost recovered nine days thereafter, and, on July 24th, the second peak of mosquito abandance was observed when the drainage began. Drainage was repeated for eight times until the final one (Sept. 13th) when the irrigation ceased completely. The period when the mosquito larvae most prevailed was estimated approximately 40 days begining from the riceplant-transplantation to the first drainage. It was fortunate to say that the parathion was applied in the middle of period giving favorable effect upon mosquito control. From the result stated above, the authors assume that if appropriate insecticide was applied twice between the riceplant-transplantation and the final drainage, or, drainage procedure was attempted twice, it will give a decisive effect upon the mosquito control in the paddy-field.