Abstract

(1) As the scientific knowledge is progressing day by day, the problem of photo toxicity might be solved with these well known insecticides. (2) In controlling insect pest, both DDT and BHC are used widely and popularly, especially the impreanted dusts which are more effective to this purpose. (3) When 5%, 10% DDT dusts and 0.5%, 1% BHC dusts are applied to the watermelon to control the insect pest, however, they have brought about chlorosis to the leaves which effect the internal structure. By examining the cross section of the treated leaves in 15-20 u thickness, it showed that the palisade and spongy parenchyma cells of the mesophyll become as a massive undifferentiated cells in which the chloroplasts are so reduced that their living functions are practically ceased and the plant soon wilted. (4) The time factor is the length of time after applying the insecticides to the plant. The effect of chlorisis spots has been shown only to the concentration of 5 % DDT dusts, at the time of the 2nd to the 3rd week. Therefore 5 % DDT concentration at the period of the 2nd and the 3rd week after applying is the correlation factor of DDT dust to watermelon plants. (5) To kill the insect pest of watermelon plants. The minimum concentration of insecticide required 5 % for DDT and 0.5 % for BHC dust while the maximum concentration of insecticide the watermelon plants capable to resist being 2.5 % for DDT, and much less than 0.5 % for BHC dust therefore these 2 insecticides are not recommended for centrolling insect pests for plants of watermelon.