ABSTRACT The rose-grain aphid Metopolophium dirhodum (Walker) and the greenbug Schizaphis graminum (Rondani) (Hemiptera: Aphididae), are two destructive aphid pests for cereals worldwide. Some studies have examined the biological and ecological characteristics of these two aphid species, however, the lack of genomic data limits in-depth studies of these two organisms. Here, we present the chromosome-level genome assemblies of M. dirhodum and S. graminum using PacBio long HiFi reads and Hi-C technology. The final genome assembly for M. dirhodum is 447.8 Mb, with 98.50% of the assembled sequences anchored to nine chromosomes. The contig and scaffold N50 values are 7.82 Mb and 37.54 Mb, respectively. A total of 18,003 protein-coding genes were predicted, of which 92.05% were functionally annotated. The final genome assembly for S. graminum is 476.1 Mb, with 99.08% of the assembled sequences anchored to six chromosomes. The contig and scaffold N50 values are 21.59 Mb and 99.65 Mb, respectively. A total of 24,368 protein-coding genes were predicted, of which 94.21% were functionally annotated. Comparative transcriptomic analyses identified a number of genes that might be related to wing dimorphism in M. dirhodum, including the insulin receptor, insulin receptor substrate, forkhead box protein O (Foxo), and ecdysone receptor. These results may provide important references for understanding the ecology, genetics, and evolution of these two organisms or even other aphid insects.

The rose-grain aphid Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) is one of the most important aphid pests for cereals worldwide. Some studies have examined the biological and ecological characteristics of M. dirhodum. However, the lack of genomic data limits in-depth studies of this organism. Here, we present a chromosome-level genome assembly of M. dirhodum using PacBio long HiFi reads and Hi-C technology. The final genome assembly is 447.8 Mb, with 98.50% of the assembled sequences anchored to nine chromosomes. The contig and scaffold N50 values are 7.82 Mb and 37.54 Mb, respectively. A total of 18,003 protein-coding genes were predicted, of which 92.05% were functionally annotated. Comparative transcriptomic analyses identified a number of genes that might be related to wing dimorphism, including the insulin receptor, insulin receptor substrate, forkhead box protein O (Foxo), and ecdysone receptor. These results may provide an important reference for understanding the ecology, genetics, and evolution of this organism or even other aphid insects.

Pesticide resistance in insects is an example of adaptive evolution occurring in pest species and is driven by the artificial introduction of pesticide. The diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), has evolved resistance to various insecticides. Understanding the genetic changes underpinning the resistance to pesticides is necessary to the implementation of pest control measures. For this reason, we sequenced the genome of 6 resistant and 6 susceptible DBMs, and inferred the genomic regions of greatest divergence between strains using two indices, Fst and θπ. Among several genomic regions potentially related to insecticide-resistance, a P450 gene, CYP6B6-like, was observed with significant divergence between the resistant and susceptible strains, with, among other SNPs, a missense mutation located near the substrate recognition site (SRS). To characterize the relative effects of directional selection via insecticide tolerance (‘strain’) as compared to acute exposure of insecticide (‘treatment’), four pairwise comparisons were carried out between libraries to determine the differentially expressed genes (DEGs). Most resistant-related DEGs were identified from comparison between strains, and enriched in pathways for exogenous detoxification including cytochrome P450 and ABC transporter. Further confirmation came from the weighted gene co-expression network analysis (WGCNA), which indicated that genes in the significant module associated with chlorantraniliprole-resistance were enriched in pathways for exogenous detoxification, and that CYP6BG1 represented a hub gene in this module. Our study thus provides a genetic foundation underlying selection for pesticide resistance and plausible mechanisms to explain fast evolved adaptation through genomic divergence and altered gene expression in insects.