Effects of Insecticide and Water Plants on Mosquito Development

The author made comparative studies of the effects of different kinds of oil, insecticide, and disinfectant on the development of mosquito larvae or chrysalises. He found from the experiments that the effects of oil increase in proportion to the thickness of the oil sheet on the water, that the effects of insecticide or disinfectant depend upon the concentration of the medical solution, and that, if subjected to insecticide and disinfectant, the chrysalis has stronger resistance than the larva, but that, on the contrary, the chrysalis has the weaker resistance when exposed to oil. He further established the fact that the light and the heavy oils, which were hitherto generally used, are relatively cheap and moreover the most effective expellants among the many tested. He showed also that it is very difficult to exterminate with oil the innumerable developed larvae and chrysalises in drains in summer, but that oil is very effective in destroying those larvae which pass the winter. Therefore he maintained that the extermination of larvae and chrysalises is to be carried on in winter. Next he experimented concerning the effects on mosquito development of the following eight species of water plants: 1) Potamogeton oxyphyllus, Miq. 2) Potamogeton crispus, L. 3) Hydrilla verticillata, Casp. var. Roxburghii, Casp. 4) Trapa natans, L. var. bispinosa, Makino. 5) Lemna paucicostata, Hegelm. 6) Spirendera polyrhiza, Schleid. 7) Hydrocharis asiatika, Miq. 8) Potamogeton Polygonifoius, pourr. The experiments clearly indicate that these species have a marked effect on the development of the mosquito. In his research as to the cause of this effect, the water plants in the dark room had no effect on the development of the larva; it began to decay, and no further work could be undertaken. This single experiment, in connection with other works, would indicate that the larvicidal action of the water plants is associated with the excessive production of oxygen caused by photosynthetic activity.