Dissipation Of Chlorpyrifos And Bifenthr In Soil And Their Period Of Validity For Termite Control

Termite is a group of socialized insect pest that causes serious damage in area south of the Yangtze River in China. Termite control nowadays relys largely on chemical insecticides. Both chlorpyrifos and bifenthrin belong to insecticide candidates recommended by Chinese Association of Property Management for prevention of termite infestation in frames. Chlorpyrifos is the most widely used one in China among the 6 recommended insecticides, and bifenthrin has also been widely applied in recent years. In present study biological activity of chlorpyrifos and bifenthrin to a subground termite, Reticulitermes flaviceps, were assessed by topical application and by soil penetration test. Five cities within area of termite infestation in south of the Yangtze River, i.e., Wuhan, Hefei, Hangzhou Quanzhou, and Chengdu, were selected to performed the field trails. Parallel dissipation studies were conducted in laboratory with soil collected from the 5 trial sites. One of the aims of present studies is to help managers in terms of selecteion of insecticides for termite prevention. Meanwhile the present studies intend to lay a scientific foundation for establishment of criteria for evaluating of chemical barrier for termite prevention, especially the criteria for evaluating of validity period of insecticides in barriers..The biological testing with Reticulitermes flaviceps indicated that, as the topical application method was used, LC50 was 0.34 mg/L for chlorpyrifos, and the value was 2.32 mg/L for bifenthrin. The soil penetration test conducted with the same species indicated that for chlorpyrifos, 4 mg/kg can be regard as critical concentration that determind whether or not the termite could drill through the 5cm length barriers spiked with chlorpyrifos and and bifenthrin. The soil penetration test also indicated that the minimum lethal concentration for chlorpyrifos was 12 mg/kg, and the value was 16 mg/kg for bifenthrin. This suggested that both chlorpyrifos and bifenthrin held contact toxicity and repellent effect towards termites in field situation, and the repellent effect seemed more outstanding for bifenthrin.The indoor dissipation studies indicated that half lifes of chorpyrifos connecting the 5 soils were in range of 41.3d to 51.9d. In outdoor dissipation studies the half lifes of chorpyrifos were in range of 35.2d to 66.6d. As for bifenthrin the half lifes were in range of 22.1d to 35.9d in indoor studies, whereas in outdoor studies they were in range of 65.8d to 152.3d. Based on data from bioassays the period of validity of chlorpyrifos in terms of termite prevention fell in range of 167～309d, with the longest period in Chengdu and the shortest one in Wuhan. As for bifenthrin the period of validity was in range of 49 to 222, with the longest period in Quanzhou and the shortest one in Wuhan.Groundwater contamination by chlorpyrifos and bifenthrin was monitored along with the soil dissipation study conducted in Hangzhou. Residue of both the 2 insecticides was detected in water samples collected 30cm beneath the top soil, and the levels were detected to be 0.01 mg/L and above. According to previously published toxicity data, the residue concentration of chlorpyrifos and bifenthrin in leachate exceeded limit of tolarence of many aquqtic species which belongs to zooplankton, crustacean, aquatic insect, fish, and so on. It is reasonable to expect, therefore, that if interchange exists between surface water and groundwater at site where the termite-prevention inasecticides are applied, aquatic communites might be obviously impacted.