The rice leaf roller, Cnaphalocroci smedinalis Guenée (Lepidoptera: Pyralidae) is a leaf-feeding pest of rice world-widely distributed. For better understanding of the pest insect, geographic sequence variation of the species were performed using the mitochondrial A+T-rich region, with the samples collected from seven Korean and six Chinese localities. A total of 94 haplotypes obtained from 187 individuals showed the length variation, ranging from 339 bp to 348 bp. The maximum divergence of 4.57% appears to evidence a substantial sequence variation, indicating the applicability of this molecular marker to the study of geographic variation. Overall, a high per generation migration ratio (Nm = 3.67742 ~ infinite), a low level of genetic fixation (FST = 0 ~ 0.11969), and no discernable isolated population were noted in the most C. medinalis populations. AMOVA analysis to find out allocation of genetic variability of C. medinalis populations has shown allocation of majority of variation to the within-population, rather than among-populations and between-region, suggesting that the C. medinalis populations in both China and Korea are largely well connected. This result is consistent with current knowledge of the dispersal ability of the species. The structure analysis of the A+T-rich region has shown that the typical structural elements found in other lepidopteran insects also is well preserved in the C. medinalis A+T-rich region (i.e., a poly-T stretch and a microsatellite-like A/T repeat).

In an effort to gain a better understanding of the nature of the population genetic structure of the pest insect, Spodoptera litura (Lepidoptera: Noctuidae), tobacco cutworms were collected from six Korean and five Chinese localities and their mitochondrial A+T-rich region and nuclear internal transcribed spacer 2 (ITS2) regions were cloned and sequenced. A total of 106 A+T-rich region haplotypes and 92 ITS2 sequence types were obtained from 158 individuals. Compared to the preliminary mitochondrial COI gene sequence data that provided all identical sequence types in all samples, the A+T-rich region and nuclear ITS2 are highly variable. Overall, a low level of genetic fixation in the A+T-rich region (FST = 0 ~ 0.02965) and nuclear ITS2 (FST = 0 ~ 0.34491), and no discernable isolated population was noted to exist among most S. litura populations. The presence of a majority of within-population variations, rather than variations among populations or between China and Korea, indicates that the S. litura populations are composed of heterogeneous individuals. The fixation index at hierarchical level of among regions shows no significance, suggesting that the S. litura populations in both Korea and China are profoundly interrelated with one another. This finding is in accord with the current knowledge that S. litura has sufficient flight capacity for dispersal.

In order to understand the nature of population genetic structure of the notorious pest insect, Spodoptera litura (Lepidoptera: Noctuidae), a total of 159 individuals of the tobacco cutworm collected from six Korean and five Chinese localities were cloned and sequenced their mitochondrial A+T-rich region. A total of 90 haplotypes ranged 324 bp ~ 372 bp in length and 0.30% ~ 4.85% in sequence divergence. Compared to the preliminary mitochondrial COI gene sequence data that provided nearly identical sequences in all samples, the A+T-rich region provided substantially high sequence variation, validating the applicability of this molecule to the study of intraspecific variation. Overall, a very high per generation migration ratio (Nm = 5.91 ~ infinite), a very low level of genetic fixation (FST = 0 ~ 0.077796), and no discernable isolated population were noted to exist among populations of S. litura, although some significant genetic differentiations were found between several pairs of populations. These results collectively suggest that the S. litura populations in both Korea and China are very well interrelated to each other. The structural analysis revealed that the S. litura A+T-rich region harbored two stretches of the [TA(A)]n sequence, the poly-A stretch, and a stem-and-loop structure that are well found in other lepidopteran A+T-rich region. Furthermore, the region harbors the 13 ~ 19-bp long T stretch and 5-bp long motif that have been suggested to function as a possible recognition site for the initiation of replication of the minor strand of mtDNA also were found.