Laboratory studies were conducted to examine the insecticidal action of agricultural chemicals against the parasite, Anicetus beneficus Ishii et Yasumatsu during 1960 and 1961. Judging from the figures obtained (as expressed by the mortality percentage) after 24 hours by the dipping method the results indicate that the four copper-mercury compounds have no effect on this parasite, but Selta (zinc dithiocarbazate 65 %) has a slight effect on it, and Sanquinon (dichlor-1, 4-naphthoquinon 35 %, tetra methyl thiuram disuiphide 20 %), Tedion, Neosappiran (p-chlorophenyl-p-chlorobenzenesulphonate 18%, bis-(p-chlorophenyl)-mehtane 7 %), G-338, Dinitrophenol and CCS have moderate effect on this. Kelthane, CMP, Methyldemeton, Ekatin (Thiometon 20 96), Fussol (monofiuoroacetamid 10 %), Bayer-4741, Sevin and EPN showed high toxic action. Residues of Tedion, Dinitrophenol and Kelthane on the surface of a laurel twig were not effective even when they were not exposed to weathering. In that instance Ekatin showed a considerable residual effect and Methyldemeton, Fussol, Hokuthion (γ-BHC 15 %), Sevin, EPN, Sumithion (0, 0-dimethyl-0-(3 methyl 4 nitrophenyl)-thiophosphate 50%) and Malathion showed high toxic residual effect against the parasite. When residues were exposed to weathering for 5 days, Hokuthion and PCP did not approximately show any toxic action. Residual effects of Ekatin, Fussol, Bayer-4741, Mehtyldemeton, Sevin and Sumithion decreased when residues were exposed to weathering for 9-10 days. Residual effect of EPN continued for 20 days. Residue of Malathion is more toxic than that of EPN. Residual effects of Parathion and DDT, when exposed to weathering for a month or so, remain still high against the parasite. Detrimental effects of insecticides on Anicetus beneficus were compared by the ratio of practical dosage against the pests to LD-50 against the parasite. Thus, the relative toxic activities of Tedion, CMP and Methyldemeton were 1.0: 4.1 : 6.5.
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