Relationship Between Cold Hardiness and Diapause in the Smaller Fruit Tortrix, Adoxophyes orana (Fischer von Roslerstamm)

Abstract

The smaller fruit tortrix, Adoxophyes orana (Fischer von Roslerstamm), overwinters at larval developmental stage. Cold-hardening is presumed to be expressed during diapause development for successful overwintering in this species. To address this hypothesis, we compared cold tolerance between diapausing and non-diapausing larvae, following overall cold tolerance assays in all stages. Supercooling points (SCPs) varied among developmental stages. The SCPs of adults (−19.8°C) were lower than those of pupae (−17.8°C) and eggs (−15.2°C). The larval stage had the most variable SCPs (−8.5 to −16.8°C) among developmental stages, which increased with larval ages. There was, however, no significant difference in SCPs between non-diapausing and diapausing larvae. Field-collected overwintering larvae had rather higher SCPs than did the laboratory-diapausing larvae. Cold tolerance also varied with developmental stages. All the stages died after a few hour exposure to low temperatures above their SCPs. Pupae were the most susceptible to low temperatures. Diapausing larvae were much more tolerant to cold temperatures than the non-diapausing larvae. Non-diapausing larvae acclimated to 0°C for 2 h had higher survival in response to lethal low temperature than did the unacclimated larvae. These cold tolerance differences were related with trehalose contents analyzed by an ion-exchange HPLC. Field-collected overwintering larvae and the laboratory diapausing larvae had significantly higher trehalose contents than did non-diapausing larvae. These results indicate that A. orana is a freeze-susceptible species and that diapause development elevates cold tolerance in this species. These also suggest that trehalose can be a major polyol conferring cold tolerance to the diapausing larvae.