Evidence for reversible change in intensity of prolonged diapause in the chestnut weevil Curculio sikkimensis

The chestnut weevil Curculio sikkimensis undergoes a prolonged larval diapause that is completed by repeated exposure to chilling and warming. We examined the possible reversibility of diapause intensity in response to temperature changes. All larvae were subjected to an initial chilling followed by incubation at 20 degrees C to force pupation of the 1-year-type larvae that require only one winter for diapause completion. We then exposed the larvae remaining in prolonged diapause to a second chilling at 5 degrees C for different lengths of time, preceded or not preceded by incubation at 20 degrees C (moderately high) and/or 25 degrees C (high) and followed by a final post-chilling reincubation at 20 degrees C. Many of the prolonged-diapausing larvae subjected only to a brief second chilling were re-activated upon reincubation. However, short exposure to 25 degrees C before this second chilling dramatically decreased the percentage of larvae completing diapause. When larvae were exposed to 25 degrees C for a short period, then incubated at 20 degrees C and subjected to the brief second chilling, many were re-activated during reincubation. The chilling time required for most of the larvae to complete diapause decreased after pre-chilling incubation at 20 degrees C and increased after incubation at 25 degrees C. These results demonstrate that diapause intensity in C. sikkimensis changes reversibly in response to changes in ambient temperature. (C) 2011 Elsevier Ltd. All rights reserved.