Introduction
The peach fruit moth (PFM), Carposina sasakii Matsumura (Lepidoptera: Carposinidae, superfamily Copromorphoidea), is a major phytophagous orchard pest of fruit such as apple, pear, peach, apricot and jujube from the families of Rosaceae and Rhamnaceae (Fig. 1 ). The hatched larvae directly bore into fruit to feed, causing losses in fruit production. PFM is one of the most severe borers on deciduous fruit in northeast Asia. It is also considered a potential risk to fruit production in most parts of the world, although PFM is currently restricted to northeast Asia and far east Russia (D. Kwon, Kwon, Kim, & Yang, 2018; Y. Z. Wang et al., 2017).
One possible of reason for the currently restricted distribution of PFM is its sensitivity to environmental factors. PFM has evolved diapause to cope with cold winter conditions and to synchronize its phenology with host plants (Toshima, Honma, Masaki, & Zoology, 1961). Both long-day and short-day photoperiods induce diapause in the last instar of PFM larvae, resulting in a diapausing cocoon (B.-Z. Hua, Zeng, & Zhang, 1998; Huang, Wang, Ye, Zhang, & Zhang, 1976). The life cycle of PFM can be univoltine or bivoltine, depending on photoperiods encountered and environmental factors like humidity (Chiba & Kobayashi, 1985; D.-S. Kim, Lee, & Yiem, 2000; Sato & Ishitani, 1976). Temperature also affects the occurrence of PFM through effects on development rate and the emergence of the overwintering generation from diapause (D. S. Kim, Lee, & Yiem, 2001; B. Zhang et al., 2016).
The effects of environmental factors as well as photoperiod on the life history of PFM provides an opportunity to investigate the genomic basis of adaptation to temperate environments in the Copromorphoidea superfamily and across Lepidoptera more generally. Candidate genes involved in climatic adaptation could then also be investigated at the geographic level, given that a combination of mtDNA and microsatellite variation indicates strong genetic differentiation among populations of the PFM among geographical populations across its native range in China (Y. Z. Wang et al., 2017). The highly variable life history of PFM on different host plants may reflect different host-associated biotypes as supported by an analysis of esterase isozyme patterns (L. Hua & Hua, 1995) and random amplified polymorphic DNA (RAPD) (Xu & Hua, 2004), although this is not yet been confirmed by direct studies on population differentiation in PFM (D. H. Kwon, Kim, Kim, Lee, & Yang, 2017; J. Wang et al., 2015).
Well-assembled genomes are increasingly becoming available as resources for tracing evolutionary adaptation across the Lepidoptera. Already there are substantial genomic resources for many moths (W. Chen et al., 2019; Cheng et al., 2017; Kanost et al., 2016; Lange et al., 2018; Ma et al., 2020; Pearce et al., 2017; Wan et al., 2019; Xia et al., 2004; Xiang et al., 2018; Xiao et al., 2020; You et al., 2013; S. Zhang et al., 2020) and butterflies (Ahola et al., 2014; Cong, Borek, Otwinowski, & Grishin, 2015; Dasmahapatra et al., 2012; Lu et al., 2019; Nishikawa et al., 2015; Zhan, Merlin, Boore, & Reppert, 2011) which are being used in comparative analyses to link genomic changes to phenotypes like the detoxification of compounds encountered in hosts (Rane et al., 2019). Available genomes provide abundant reference points for investigating evolution across the Lepidoptera, although most species sequences so far are from the Papilionoidea, Noctuoidea, Bombycoidea and Pyraloidea, with less genomic information available for the Carposinidae (Copromorphoidea) despite the importance of this group as agricultural pests.
In the present study, we report on a chromosome-level genome of PFM which was de novo assembled based on sequences obtained from the PacBio and Illumina platforms and assembled at the chromosome level with the Hi-C technique. We compare features of the PFM genome with those of eleven other moths, focusing particularly on detoxification gene families important in host adaptation and pesticide resistance, contributing to ecological niches occupied by species (Rane et al 2019). As an initial study using the newly assembled genome, we investigate transcriptomic changes induced by long-day and short-day photoperiods that induce diapause in PFM larvae, and we identify genes involved in these responses which are critical to climatic adaptation by PFM.