Molecular characterization of heat shock protein 70 cognate cDNA and its upregulation after diapause termination in Lycorma delicatula eggs

Since the sudden introduction of Lycorma delicatula into Korea in 2006, annual outbreaks of the species have seriously damaged various forest trees and horticultural plants, with grape vines being particularly affected. It is a univoltine species that overwinters during the egg stage by entering embryonic diapause. However, the mechanisms in relation to diapause of L. delicatula eggs remain unknown. Microscopic observation of diapausing eggs has shown that embryonic development was arrested at blastokinesis. Egg masses were collected monthly from a grape vineyard in the Daegu area, from December 2012 to April 2013, and incubated at 25. °C until hatching. When the duration of overwintering was longer, the hatching rate was higher, the hatching duration was shorter, and the initial hatch date was occurred earlier. We elucidated the full cDNA sequence of the heat shock cognate 70 (hsc70) gene of L. delicatula. Quantitative real-time RT-PCR showed that the hsc70 expression level was very low in eggs collected from November to February but much higher in eggs collected in the field during March. Furthermore, hsc70 expression levels gradually increased postdiapause, until hatching at 25. °C. Our results suggest that diapause termination in L. delicatula eggs requires a chilling period, which also facilitates postdiapause development. In addition, hsc70 may play a role in the resumption of embryonic development in eggs emerging from diapause.