Residual effect of diazinon emulsion to larvae of the mosquito, Culex pipiens pallens in ditches

Abstract

The field tests to estimate the residual effect of diazinon emulsion on larvae of the common house mosquito, Culex pipiens pallens, were carried out in ditches in Kawasaki City in the period from Sept. 1 to Sept. 25, 1960. Half ppm to the volume of water of diazinon was sprayed in ditches and the effect on mosquito larvae was estimated daily till 6 to 10 days after the application. The results were summarized as follows : After the application, mosquito eggs decreased in minimum numbers after 2 to 3 days, reincreased gradually, and after 6 days recovered nearly to the level before the application. In most cases, number of larvae decreased in minimum 1 day after the application and that of pupae after 2 days. Average period from the application to the reappearance of 1st and 2nd instar larvae was 4.2 days, that of 3rd and 4th instar larvae was 7.1 days and that of pupae was 8.6 days. Therefore the authors were led to the conclusion that the real residual effect of diazinon was almost none or 2 or 3 days at most and that the application of once a week was necessary for the practical control of the larvae.