Cross resistance of malathion resistant strain of Nilaparvata lugens and its biochemical aspects

The resistant strain(R)of brown planthopper selected by malathion held 184 4 fold resistance to malathion and showed obvious cross resistance to all the acetylcholine receptor targeting insecticides tested,but not to fenvalerate.Further study demonstrated that TPP had significant synergism on malathion(SR:9 15)and some on fenobucarb(SR:2 38),and DEM had some synergism to malathion(SR:2 32)and to fenobucarb(SR:1 42)in R strain.Biochemical assay showed that R strain had esterase activity 14 67 times that in susceptible strain(S),GST with CDNB 1 52 and MFO only 1 11.And TPP could significantly inhibit the esterase activity in R strain,and DEM also could inhibit the GST activity to some extent in R strain.It is concluded that the esterase and GST played an important role in the malathion resistance and the cross resistance to fenobucarb to different extents.