Abstract
The effect of three synergists on the toxicity of three insecticides was determined and some biochemical characteristics were compared among several strains of the brown planthopper. Aliesterase activity was proportional to the resistance level to malathion and fenitrothion. Aliesterase activity was inhibited by IBP in the order of 10X-8M, and IBP exhibited highly synergistic activity with malathion and fenitrothion but not with propoxur. There was no clear difference in glutathione S-transferase activity among strains evaluated. Piperonyl butoxide did not show any synergistic activity with malathion, fenitrothion or propoxur. Low sensitivity of acetylcholinesterase was found in the resistant strains and selection with propoxur resulted in an increase in the frequency of individuals having this tendency, along with an increase in the resistance level to propoxur.
