Studies of molecular mechanisms on negatively correlated cross resistance in the green rice leafhopper, Nephotettix cincticeps Uhler

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By analyzing the sensitivity of acetylcholinesterase (AChE) of individual insects in vitro, we developed a simple monitoring method for insecticide resistance in the green rice leafhopper, Nephotettix cincticeps Uhler. By using this mehtod, we found that a combination of insecticides (N-methyl carbamate insecticides and monocrotophos) showed a negatively corelated cross resistance at the AChE inhibition level in vitro. However, this phenomenon was not found by the bioassay (toxicity test). High aliesterase actrivity in the insecticide resistant green rice leafhopper was thought to be a cause of this phenomenon. We bred an insecticide resistant strain which shows a low aliesterase activityby by back cross experiment between insecticide resistant and susceptible strains. By the bioassay, we could find that the aliesterase activity in the resistant strain was a cause that we could not find negatively correlated cross resistance in the field strains of green rice leafhopper. To calrify the mechanisms of negatively correlated cross resistance between W-methyl carbamates and monocrotophos at the molecular level, we analyzed the aminoacid sequence of AChE gene and found that there was no difference in the aminoacid sequence between insecticide susceptible and resistant strains of the green rice leafhopper. Thus, the molecular mechanism of cross resistance in the green rice leafhopper was thought to be derived from the post translational modification. We would like to find out what type of translational modification is involved in the mechanisms of megatively correlated cross resistance and find out the whole story of this interesting phenomeno, negatively correlated cross resistance.