Some factors affecting the residual effects of the insecticides to the adult housefly and the mosquito

The differences of residual effectiveness of insecticides applied to different surfaces were studied using DDVP, diazinon, ronnel, lindane, malathion, Sumithion, Baytex, dieldrin and p, p'-DDT. These were applied in ethanol solution to glass plate and filter paper. Their effects were evaluated in laboratory tests using the adult houseflies, Musca domestica vicina, and the house mosquito, Culex pipiens pallens. All the insecticides, except DDVP, applied to the glass plate were more effective than those applied to the filter paper, when the insects were brought into contact within 24 hours after the application. The effect of the more volatile DDVP was reduced rapidly because of the high initial loss of the toxicant on the glass plate; therefore the mortality observed on the glass plate was lower than that observed on the filter paper 8 to 24 hours after the application. In general, it has been found that insecticides having the steeper slopes of the ld-p line produce larger differences of LC_<-50>'s between the glass plate and the filter paper when compared immediately after application. In residual effects highly volatile chemical, for example DDVP, showed higher mortalities on the filter paper in comparison to the glass plate, and the differences of LC_<-50>'s between the latter and the former became greater as time elapsed. Although moderately volatile insecticides such as diazinon, ronnel and lindane, applied to the glass plate gave higher mortalities for a few days, their LC_<-50>'s obtained from 4 to 8 days after the application were almost equal on both types of treated surfaces. After 8 days higher mortalities were observed on the filter paper than on the glass plate, the differences of LC_<-50>'s increasing in accordance with the time elapsed. The effects of residues from insecticides with low volatility, i. e. malathion, Sumithion, Baytex, were higher on the glass plate during most of the 64 days test period, although the differences of LC_<-50>'s were reduced as age of the residues increased. Throughout the entire test period of 64 days, insecticides of low volatility, dieldrin and DDT, showed high mortalities when applied to the glass plate; those effects, or the differences of LC_<-50>'s were almost the same on both surfaces as those obtained initially after the application. In interpreting these experiments, it is considered that the adsorption of solutions containing toxicants on or into the treated surface, the release of toxicants into the air by evaporation, and the translocation of toxicants from treated surface to untreated, were the factors affecting the differences in residual effects of insecticides applied to different surfaces as residual sprayings.