Light is an important environmental signal for most insects. The Oriental Armyworm,Mythimna separata, is a serious pest of cereal crops worldwide, and is highly sensitive to light signals during its developmental and reproductive stages. However, molecular biological studies of its response to light stress are scarce, and related genomic information is not available. In this study, we sequenced andde novoassembled the transcriptomes ofM. separataexposed to four different light conditions: dark, white light (WL), UV light (UVL) and yellow light (YL). A total of 46,327 unigenes with an average size of 571 base pairs (bp) were obtained, among which 24,344 (52.55%) matched to public databases. The numbers of genes differentially expressed between dark vs WL, dark vs UVL, dark vs YL, and UVL vs YL were 12,012, 12,950, 14,855, and 13,504, respectively. These results suggest that light exposure altered gene expression patterns inM. separata. Putative genes involved in phototransduction-fly, phototransduction, circadian rhythm-fly, olfactory transduction, and taste transduction were identified. This study thus identified a series of candidate genes and pathways potentially related to light stress inM. separata.

Many insects enter a developmental arrest (diapause) that allows them to survive harsh seasonal conditions. Despite the well-established ecological significance of diapause, the molecular basis of this crucial adaptation remains largely unresolved. Sitodiplosis mosellana (Gehin), the orange wheat blossom midge (OWBM), causes serious damage to wheat throughout the northern hemisphere, and sporadic outbreaks occur in the world. Traits related to diapause appear to be important factors contributing to their rapid spread and outbreak. To better understand the diapause mechanisms of OWBM, we sequenced the transcriptome and determined the gene expression profile of this species. In this study, we performed de novo transcriptome analysis using short-read sequencing technology (Illumina) and gene expression analysis with a tag-based digital gene expression (DGE) system. The sequencing results generated 89,117 contigs, and 45,713 unigenes. These unigenes were annotated by Blastx alignment against the NCBI non-redundant (nr), Clusters of orthologous groups (COG), gene orthology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. 20,802 unigenes (45.5% of the total) matched with protein in the NCBI nr database. Two digital gene expression (DGE) libraries were constructed to determine differences in gene expression profiles during diapause and non-diapause developmental stages. Genes related to diapause were analyzed in detail and in addition, nine diapause-related genes were analyzed by real time PCR. The OWBM transcriptome greatly improves our genetic understanding and provides a platform for functional genomics research of this species. The DGE profiling data provides comprehensive information at the transcriptional level that facilitates our understanding of the molecular mechanisms of various physiological aspects including development and diapause stages in OWBM. From this study it is evident that various genes coding metabolic enzymes are crucial for diapause and metamorphosis.

The wheat midge, Sitodiplosis mosellana, is an important pest in Northern China. We tested the hypothesis that the population structure of this species arises during a range expansion over the past 30 years. This study used microsatellite and mitochondrial loci to conduct population genetic analysis of S. mosellana across its distribution range in China. We found strong genetic structure among the 16 studied populations, including two genetically distinct groups (the eastern and western groups), broadly consistent with the geography and habitat fragmentation. These results underline the importance of natural barriers in impeding dispersal and gene flow of S. mosellana populations. Low to moderate genetic diversity among the populations and moderate genetic differentiation (F_ST = 0.117) between the two groups were also found. The populations in the western group had lower genetic diversity, higher genetic differentiation and lower gene flow (F_ST = 0.116, Nm = 1.89) than those in the eastern group (F_ST = 0.049, Nm = 4.91). Genetic distance between populations was positively and significantly correlated with geographic distance (r = 0.56, P<0.001). The population history of this species provided no evidence for population expansion or bottlenecks in any of these populations. Our data suggest that the distribution of genetic diversity, genetic differentiation and population structure of S. mosellana have resulted from a historical event, reflecting its adaptation to diverse habitats and forming two different gene pools. These results may be the outcome of a combination of restricted gene flow due to geographical and environmental factors, population history, random processes of genetic drift and individual dispersal patterns. Given the current risk status of this species in China, this study can offer useful information for forecasting outbreaks and designing effective pest management programs.