Effects of abamectin selection on the genetic differentiation within Plutella xylostella （Lepidoptera： Plutellidae） based on amplified fragment length polymorphism

Diamondback moth, Plutella xylostella （L.） is one of the most serious insect pests for its remarkable ability to develop resistance to virtually every insecticide that has been used against it. In the present study, amplified fragment length poly- morphism （AFLP） is used to study the genetic differentiation as well as the effects of abamectin-selection on population genetic differentiation for P. xylostella. A dendrogram was constructed from the matrix of genetic distances using the STATISTICA software （Version 4.5） and unweighted pair-group method with arithmetic averages （UPGMA）. The data demonstrated that compared to the susceptible strain （ABM-s）, the heterozy- gosity in the abamectin-resistant strain （ABM-r） decreased with the increased selection pressure and resistant level. When the resistance ratio was below 4.3, there was no sig- nificant differentiation at the genome DNA level. When the resistance ratio reached 5.8, a fairly significant differentiation began to appear, and when the resistance ratio reached and exceeded 8.1, there appeared a significant genetic differentiation. The results suggest that abamectin selection is associated with increased genetic polymorphism in P. xylostella.