Sample collection and rearing
We established a laboratory strain of PFM from 30 larvae collected from an apple orchard in the Beijing area of China in July 2018. This strain was maintained for five generations on apple (Malus pumilaMill) in the laboratory under 25 ± 1 °C, a relative humidity of 75 ± 5%, and a photoperiod of 15L : 9D (ND, normal-day condition). Eggs were laid on filter paper and moved to ripe apples before hatching. Larvae developed in the apples and the last (fifth) instar larvae left the fruit to pupate on prepared sawdust. Samples used in genome sequencing and RNA-seq were from this strain.
In order to induce diapause in larvae, we moved batches of newly hatched larvae to long-day and short-day photoperiodic conditions before they bored into apple for feeding. The long-day condition (LD) was set to a photoperiod of 22 L : 2 D, while the short-day condition (SD) was set to a photoperiod of 8 L : 16 D. Both treatments were conducted under 25 ± 1 °C, and a relative humidity of 75 ± 5%. The last instar larvae leaving the fruit were collected and stored in RNAlater at −80 °C (Sigma-Aldrich, St. Louis, USA) for subsequent RNA-seq library construction.