Chlorpyrifos-resistant Inheritance And Linkage Mapping In The Diamondback Moth, Plutella Xylostella

The diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae), is one of several model insects used for resistance research. In recent years, studies on the inheritance of insecticide resistance in DBMs, have been published, and linkage mapping has been studied using molecular marker methods. However, the inheritance of resistance to chlorpyrifos in DBMs and the linkage map associated with chlorpyrifos resistance have not been reported. This study examines the inheritance of chlorpyrifos resistance and the linkage mapping in DBMs using SSR markers. This research forms the basis for resistance gene mapping and cloning of the resistance gene.The chlorpyrifos-resistant (FZ-CR) DBM strain and the susceptible (FZ-CS) DBM strain were used for reciprocal crosses and backcrosses. The FZ-CR strain demonstrates a 280.2-fold resistance to chlorpyrifos compared with the FZ-CS strain. The progeny resulting from reciprocal crosses showed 73.19- and 64.75-fold resistance to chlorpyrifos, and the LC50 level showed no significant difference, indicating that chlorprifos resistance in the FZ-CR strain is autosomal. Values for the dominance level were between 0.5235 and 0.4802 (according to the Stone formula) indicating that chlorpyrifos resistance in the FZ-CR strain is incompletely dominant. In the LD-P curve for the backcross progeny of F1 and FZ-CS, no distinct plateau was observed at 50% mortality. Similarly, no distinct plateau was observed in the LD-P curve at the 25% or 75% mortality for the F2 progeny (the inbred progeny of the F1 generation which were obtained by the reciprocal cross). This suggests that chlorpyrifos resistance may be controlled by more than one gene. The χ2 test for the goodness of fit between the observed and predicted values under the assumption of monofactorial inheritance further eliminates the single-gene hypothesis.The genetic group was created using the resistant (FZ-CR) and susceptible (JP-S) strains as the material. Among the 200 pairs of SSR markers selected,72 pairs of SSR markers were stably inherited between the resistant (FZ-CR) and susceptible (JP-S) strains. A total of 72 SSR polymorphic markers were genotyped in the BC) population that was derived from an FZ-CR male and an F1(JP-S(♀)×FZ-CR(♂)) female. The segregation data were analyzed using MAPMAKER 3.0 with LOD=3.0 and 31 SSR polymorphic markers were assigned into 6 linkage group. The BC2 population that was derived from an FZ-CR female and an F1 (JP-S(♀)×FZ-CR(♂)) male was used to calculate the genetic distance, and the total map length was estimated to be 253.3 cM. The χ2 test indicated that there was no significant difference between the control group and the treated survival group. Thus, the resistance locus could not be mapped to the corresponding linkage group, and further work is required.