Abstract
This study was conducted to examine the action of cartap controlling the infection of rice dwarf disease with special references to the treatment of seedlings in nursery trays prior to the mechanical transplanting. The viruliferous leafhoppers were caged on rice seedlings in nursery trays which had been soaked over night in aqueous solutions of cartap hydrochloride. The treatment with 15ppm reduced the infection to 1/8 of the untreatment. In the treatment with 50ppm, the infection was suppressed almost completely. In these tests about 80% of the insects were poisoned until 6hr following the release. In the transplanted seedlings treated with the 20-ppm cartap solution in the nursery trays, the infection was reduced to 50% of the untreatment, though the rates of heavily poisoned insects did not exceed 15% during 24hr. The probing frequency on the plants decreased even in the insects showing no appearance of the intoxication. Results of other experiments using artificial membranes also supported the effect on the probing activity. It is concluded that the rapid lethal action of cartap and the depressive effect on the transmitting behavior of the leafhopper at sublethal doses account for the reduction of the rice dwarf disease.
