Abstract
Laboratory experiments were carried out to assess the residual effect of 10 insecticides, i.e., lindane, dieldrin, diazinon, malathion, Dibrom, DDVP, Dipterex, ronnel, Baytex, Sumithion to larvae of Culex pipiens using glass vessels. The effective weeks during which 3.2ppm emulsions showed the mortality over 90% were 37 weeks in Sumithion, 31 weeks in ronnel, 33 weeks in Baytex, 19 weeks in diazinon, 33 weeks in lindane, 3 weeks in dieldrin, 5 weeks in Dipterex and DDVP, a week in malathion and less than a week in Dibrom. The persistency index, C_i, was calculated from the following formula : C_i=A/(B_i)×100 A : LC-50 immediately after diluting the emulsifiable concentrate. B_i : LC-50 i weeks after the dilution. The persistency of insecticidal emulsions obtained from the above index descended in the following order : lindane (C_<26> : approximately 40), Baytex, dieldrin and diazinon (C_<39> : 1.5-6), Sumithion and ronnel (C_<37> : 0.4-0.5), Dipterex, DDVP and malathion (C_<9-10> : 0.1-0.3), and Dibrom (C_1 : approximately 0.2).
