室内条件下におけるアカイエカおよびコガタアカイエカに対する PH 60-40 の致死効果

Abstract

We have evaluated lethal effects of the insect growth regulator, PH 60-40 [N-(4-chlorophenyl)-N'-(2,6-difluorobenzoyl) urea], against the larvae of Culex pipiens pallens and Culex tritaeniorhynchus. A 25% wettable powder formulation of PH 60-40 was used for the tests. All test were conducted in 300ml glass vessels each containing 200ml of distilled and deionized water. A certain amount of PH 60-40 was added into each vessel to make suspensions with desired concentration of the active ingredient. Twenty 3rd or 4th instar larvae were introduced in each vessel and about 10mg of dry beer yeast were added as food every 2 days. The temperature of water in these glass vessels remined at 23°±1℃. Since mortality occurs during larval molts, in the pupal stage, and at the unsuccessful emergence of adults, all of these forms were checked every day until all survived larvae became adults to determine total or cumulative mortality. The calculated mortality, determined from the number of adult emergence, was corrected by Abbot's formula. The LC-50 dosage were obtained from eyefitted curves of the corrected percent mortality obtained at each dose. Larval emergence was not inhibited in the egg rafts of Culex pipiens pallens laid 12-18hr prior, but development of the newly hatched young larvae was. At the rate of 0.2 and 0.1 ppb PH 60-40 inhibited adult emergence almost completely. LC-50 dosages of PH 60-40 against larvae of Culex pipiens pallens were 0.035 ppb at the 3rd instar, 0.062 ppb at the 4th instar, and those against Culex tritaeniorhyncus were 0.042 ppb at 3rd instar, 0.060 ppb at the 4th instar, respectively. At the rate of 0.5 ppb, adult emergence from the 4th instar larvae of Culex pipiens pallens was completely inhibited, even larvae tested were introduced 7 days after the treated medium prepared. However, at the rate of 0.125 ppb concentration the lethal effects were decreased after 7 days definitely. In conclusion, PH 60-40 possess a significant lethal activity against the larvae of Culex pipiens pallens and Culex tritaeniorhynchus and appears to be a promissing candidate for mosquito controlling agent.