Molecular analysis of overwintering diapause

Publisher Summary Diapause is a genetically determined, hormonally mediated state of suppressed development, and is an important adaptive mechanism for insect survival during unfavourable environmental conditions, such as low winter temperatures. The spruce budworm, Choristonuera fumiferana, overwinters as a diapausing second-instar larva. Molecular analyses of larvae in prediapause, diapause, and postdiapause stages led to the identification of sugars and proteins that are related to diapause or overwintering. C . fumiferana produces the disaccharide trehalose and proteins, such as diapause associated proteins 1&2 and glutathione S-transferase that are diapause related. The glycerol and the defensin-like protein that the larvae produce appear to be related to the overwintering process. Glycerol production and synthesis of defensin-like protein are clearly overwintering related events, and these happen only after the larvae are exposed to cold treatment for certain lengths of time. If the larvae are not exposed to the cold treatment, they fail to synthesize glycerol or defensin-like protein. On the other hand, increases in trehalose levels and synthesis of CfDAPl and CfDAP2, as well as increased synthesis of CfGST, occur as soon as the larvae hatch and start preparing for diapause. They also start spinning hibemacula at this time. These are probably diapause-related events. Absence of ecdysteroids in the diapausing second instars prevents molting and metamorphosis, allowing them to overwinter in this stage. This chapter describes the simultaneous occurrence of obligatory diapauses and the overwintering process in the second-instar larvae of the spruce budworm, C. fumiferana . However, these two physiological events can be distinguished from each other on the basis of some of the biochemical changes that occur in these larvae during the obligatory overwintering diapause.