Abstract
The present investigation was undertaken to modify the oil-water flotation method for the purpose of a more effective extraction of larvae and pupae of aquatic midges from a soil sample. First, a sample of soil was stirred by a magnetic stirrer for more than three minutes in a beaker containing CaCl_2 solution having a certain specific gravity to remove the insects from the soil tubes and to float them to the water surface. Secondly, the floating insects were separated from other floating materials by use of benzene and air evacuation. In this process the specific gravity of a solution should be determined in correspondence with the total time required for the treatment. Also the pupae which could be scarcely wetted by benzene should be pushed up to the benzene layer by large buoyancy in a solution having a specific gravity above 1.30. Lastly, the insects were locked in the benzene plug upon freezing of benzene and examined after the benzene plug was thawed.
