Ecdysteroid titers and expression of Halloween genes and ecdysteroid receptor in relation to overwintering and the long larval phase in the seabuckthorn carpenterworm, Holcocerus hippophaecolus

Abstract

AbstractThe cytochrome P450 enzymes encoded by the Halloween genes – spook (spo), phantom (phm), disembodied (dib), shadow (sad), and shade (shd) – catalyze a series of hydroxylation steps resulting in the active molting hormone 20‐hydroxyecdysone (20E). This study investigated 20E and ecdysone titers and the expression profile of Halloween genes and ecdysone receptor (EcR) during larval, pupal, and adult stages in seabuckthorn carpenterworm, Holcocerus hippophaecolus Hua (Lepidoptera: Cossidae). Hh‐spo, Hh‐phm, Hh‐dib, and Hh‐sad showed predominant expression in the prothoracic gland at the larval stage, whereas Hh‐shd and Hh‐EcR were significantly expressed in the fat body. The mRNA levels of Hh‐spo, Hh‐phm, Hh‐dib, Hh‐shd, Hh‐sad, and Hh‐EcR were lowest from late October to middle April, when the insects were in overwintering dormancy, but began to increase from May each year, when the insects were terminating quiescence. Concomitant with the changes in these genes, 20E and ecdysone titers gradually increased during the 4‐year life cycle of H. hippophaecolus. These data indicate that the seasonal expressions of Hh‐spo, Hh‐phm, Hh‐shd, and Hh‐EcR play crucial roles in quiescence of the overwintering period, and are responsible for the long larval phase and the exact timing and amplitude of the ecdysteroid titer required for the coordination of growth and development in H. hippophaecolus.