Studies on residues and degradation dynamics of dichlorvos in mulberry leaves

【Objective】 In order to provide scientific basis for setting up a safe picking time of sericulture production,the research studied the residues and degradation dynamics of dichlorvos in mulberry leaves and the toxicology of pesticides to silkworm.【Method】 80% dichlorvos EC was sprayed on mulberry at 1 500 g/hm2.The mulberry leaves were sampled after 2 h,1,2,3,4,5,6,7 and 10 d.The dichlorvos residues in mulberry leaves were detected with GC.The third instar silkworms were fed different replenishment of mulberry leaves sampled after DDVP spraying in order to observe and record silkworms' poisoning and death.【Result】 The result showed that with the extension of the sampling time after applying,the quantity of DDVP residue in mulberry leaves reduced gradually and the mortality of silkworms caused by mulberry leaves decreased rapidly,the dynamic equation of dichlorvos in mulberry leaves corresponded to first order kinetic equation,the half life being 0.99 d.The mortality rate of third instar silkworms which were fed mulberry leaves sprayed with dichlorvos EC was 0% on the fifth day.【Conclusion】 The safe picking period for silkworm-raising with mulberry leaves is at least five days after 80% dichlorvos EC is sprayed at 1 500 g/hm2.