EFFECT OF VARIOUS CHEMICALS UPON THE GROWTH OF DAPHNIDS

Abstract

Twenty two chemicals were tested for their effectiveness in killing daphnids, and at the same time their maximum innocuous concentrations towards blue green algae were determined. It was observed that diethyl-p-nitrophenylthiophosphate is most effective as a daphnidkiller, and is, at the same time, innocuous for the growth of blue-green algae.
For several years Parathion or Folidol, which is innocuous for the rice plant in a concentration of 250ppm, has been used as an insecticide in rice fields, and now it is also shown to kill daphnids in a concentration of 0.00075ppm. Assuming that the depth of the water in a paddy field is 10cm, the volume of water is 400, 000liters per acre. If the diluted solution of only 20ml Parathion is sprayed on this field, the concentration of the drug in the water of the field will become 0.05ppm. This concentration is about one hundred times the minimum lethal concentration of daphnids, and therefore this drug is remarkably efficient.
It should be remembered, on the other hand, that daphnids are known to be a favourite food for fresh-water fish. If daphnids are killed by spraying of the drug on the paddy field sooner or later it may affect the growth of fresh-water fish in the paddy field water by the continued scarcity of daphnids.