1 ∣ INTRODUCTION
Since the launch of the 5,000 Insect Genome Project (i5k) in 2011, at least 497 insect genomes have been sequenced and annotated according to the NCBI database (Robinson et al., 2011). Most of the sequenced insect genomes are either important agricultural pests, vectors for pathogens, or species that serve as model organisms (Xianhui et al., 2014). Silkworm (Bombyx mori ), honeybee (Apis cerana ) and WWS (Ericerus pela ) are the top three resource insects that have provided significant economic or medical benefits to humans for millennia. The genomes of both honeybee and silkworm have been sequenced and extensively annotated, whereas high-quality genomic data for WWS is still absent so far (Consortium, 2006; Xia et al., 2004). Found in the subtropical and temperate regions of China, Japan and Russia (Supplementary Fig. 1), WWS-derived white wax has been extensively used in printing, pharmaceutical, food and cosmetic industries because of its special chemical properties (Ma et al., 2018; Wang et al., 2017).
The evolutionary origin of the insect metamorphosis is a much-debated mystery in biology. Wing development in insects occurs during metamorphosis, however, the evolutionary drivers led up to the invention of metamorphosis are still poorly understood (Misof et al., 2014). Juvenile hormone mediates metamorphosis in a range of insect species (Azinna et al., 2018; Stillwell et al., 2010). Research on firebugs has shown how juvenile hormone counteracts ecdysone during the nymph instar in hemimetabolous insects (Barbora et al., 2011; Slama & Williams, 1965). During the evolution of metamorphosis, a heterochronic shift in the time of the appearance of juvenile hormone during embryogenesis appears to have interrupted the ancestral growth trajectory in the developing insect (Gilbert, 1994). Previous studies noted that juvenile hormone plays a crucial role in mediating neoteny of different insect species. Scale insects such as WWS convergently acquired a unique mode of metamorphosis referred to as neometaboly, which is reminiscent of holometaboly (Vea et al., 2016). WWS males produce wax during the nymph stages and form winged adults, resembling a holometabolous fate (Supplementary Fig. 2). Females, however, remain stationary and appear to follow a hemimetabolous route (Qi et al., 2019). Accordingly, WWS represents an attractive research model not only to investigate the adaptive mechanisms by which a herbivorous parasite overcomes plant defense systems, but it also serves as an excellent model for the evolutionary relationships between hemimetabolous and holometabolous insects. In this study, we comprehensively analyzed the developmental differences between males and females using high-quality whole genome data of WWS, transcriptome profiling and DNA methylation. Our study paves the way to understand the developmental processes during metamorphosis and the hormone antagonism effect the sexual differentiation of metamorphosis in insects.