Abstract
Insecticidal activities of 13 butyl- and amyl-substituted phenyl carbamates on the smaller brown planthopper, Laodelphax striatellus FALLÉN, and the green rice leafhopper, Nephotettix cincticeps UHLER, were evaluated by the dry film method. The relationship between the chemical structure of compounds and their biological activities, reported in previous papers, have also been taken into observation in the present study. 2-sec-Butylphenyl N-methylcarbamate (BPMC), 3-tert-butylphenyl N-methylcarbamate (TBPMC), and 3-tert-amylphenyl N-methylcarbamate (TAPMC) showed high toxicity to planthoppers and leafhoppers. The LD50 values of these 3 carbamates by the dry film method and by the topical application method were also determined. Most of the carbamate insecticides, except TBPMC and carbaryl, showed high toxicity to the smaller brown planthopper in their gaseous state. KT50 values of BPMC, TBPMC, and TAPMC were nearly the same as with other carbamate insecticides with regard to the smaller brown planthopper, but somewhat larger to the green rice leafhopper. The increase of LD50 values of BPMC, TBPMC, and TAPMC with descending temperature was observed to be little on the green rice leafhopper, and was as large as that of carbaryl on the smaller brown planthopper. The results of spraying tests, using the rice plants cultivated in Wagner's pots, showed that the residual insecticidal activities of TBPMC and TAPMC were comparatively large, but that of BPMC was small. Insecticidal activities of TBPMC and TAPMC reached its maximum a little later than PHC (2-isopropoxyphenyl N-methylcarbamate) and MIPC (2-isopropylphenyl N-methylcarbamate) by application into pot water. Their residual effects were as large as those of PHC and MIPC with respect to the smaller brown planthopper, but were inferior to those of PHC and MIPC when used on the green rice leafhopper. The residual effect of BPMC lasted longer than carbaryl but shorter than PHC and MIPC.
