1 INTRODUCTION
The rose-grain aphid Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) is one of the most common and economically important aphid pests for cereals, including wheat, barley, rye and oat, worldwide (Cannon, 1986; Honek, 1991; Ma et al., 2004; Li et al., 2020). M. dirhodum is native in the Holarctic and was then introduced to North America, South America, South Africa, Europe, Oceania and Eastern Asia (Honek et al., 2018; Blackman and Eastop, 2000). In the continental climate of central Europe, M. dirhodum is usually the most abundant aphid species on cereals (Honek et al., 1987, 2018; Praslicka et al., 1996).
Damage caused to cereals by M. dirhodum takes several forms. These include sucking the juice from wheat leaves, stems and young ears, which further results in the deterioration of plant nutrition (Holt et al., 1984), defecating sticky honeydew that further obstructs photosynthesis and reduces wheat quality (Jiang et al., 2019), and transmission of a number of pathogenic plant viruses, including the barley yellow dwarf virus (Kennedy et al., 2005). Both nymphs and adults of this aphid may cause yield losses of 27–30% during the latter part of flowering stages of wheat (Holt et al., 1984; Chopa et al., 2012).
Recently, several studies have focused on the population dynamics (Honek et al., 2018), control methods (Cambier et al., 2001; Chopa et al., 2012) and symbiotic microorganisms (Telesnicki et al., 2012) of M. dirhodum . However, the challenge to developing a further understanding is the lack of genomic resources for this pest. To date, chromosome-level genomes with annotation information for several aphid species, including Acyrthosiphon pisum (International Aphid Genomics Consortium., 2010), Sitobion miscanthi (Jiang et al., 2019), Eriosoma lanigerum (Mathers et al., 2021) and Rhopalosiphum maidis (Chen et al., 2019), are available, which will be very helpful for the further study of these aphids. Here, we report the genome sequence of M. dirhodumassembled by incorporating Pacific Biosciences (PacBio) long HiFi reads and Hi-C technology. Subsequently, gene prediction, functional annotation and phylogenetic analysis were also performed. The genomic resource developed here for M. dirhodum is valuable for understanding its genetics, development and evolution and will provide an important reference for the study of other insect genomes.
M. dirhodum , like most aphids, can produce wing morphs when experiencing crowding, poor nutrition and temperature or photoperiod changes (Müller et al., 2001; Braendle et al., 2006; Zhang et al., 2019). Wing dimorphism in insects is an adaptive switch to environmental changes. Specifically, wingless morphs allocate more resources to reproduction, enabling rapid colony growth. Winged morphs are devoted to dispersal, which enables them to look for new habitats and food resources. Moreover, winged morphs are better at long-distance migration and host alternation, thus causing more serious host damage and virus transmission (Zhang et al., 2019). Therefore, understanding the molecular mechanisms of M. dirhodumin triggering wing dimorphism is important for its effective control. In the present study, we constructed and sequenced RNA libraries of winged and wingless M. dirhodum from third- and fourth-instar nymphs and adults. Differentially expressed genes between the winged and wingless populations were analyzed and identified according to the current assembly of the M. dirhodum genome. The results lay a solid foundation for further study of the molecular mechanisms of wing dimorphism in M. dirhodum or other insects.