Cold tolerance and trehalose accumulation in overwintering larvae of the codling moth, Cydia pomonella (Lepidoptera: Tortricidae)

Abbas Khani,Saeid Moharramipour,Mohsen Barzegar

doi:10.14411/eje.2007.057

Abstract

Seasonal variations in the supercooling point, survival at low temperatures and sugar content were studied in field-collected codling moth larvae. The supercooling point of field-collected larvae decreased significantly from a mean value of -13.4Â°C in August 2004 (feeding larvae) to -22.0Â°C in December 2004 (overwintering larvae). Survival at -20Â°C/24 h was 0% during early autumn, whereas it increased to approximately 60% during winter. The survival at low temperature was well correlated with the supercooling point. The supercooling point of the diapause destined larvae decreased from -16.9 to -19.7Â°C between September and October as the larvae left the food source and spun a cocoon. For early-diapause larvae, exposure to 5Â°C/30 days has an additional effect and decreased the supercooling point from -19.7 to -21.3Â°C. One-month exposure of overwintering larvae to 5Â°C led to a mortality of 23% in early diapause larvae, while only 4% of diapause larvae died after acclimation. Overwintering larvae accumulated trehalose during winter. There was approximately a threefold increase in trehalose content between larvae at the onset of diapause (5.1 mg/g fresh weight) and larvae in a fully developed diapause (18.4 mg/g fresh weight) collected in January. Trehalose content was correlated with supercooling capacity, survival at low temperatures and chilling tolerance, suggesting that trehalose may play some role in the development of cold tolerance in this species.

Highlights

Cold hardiness and diapause are essential components of winter survival for most insects in temperate zones (Denlinger, 1991)
The larvae which were collected from infested fruits at this time had a mean SCP of –16.9 ± 1.1°C with a range from –14.4 to –19.8 °C, while early diapausing larvae which were collected from silken cocoons in early October, had a mean SCP of –19.7 ± 0.5°C
We describe some of the physiological and biochemical features of cold hardiness in a wild population of C. pomonella with special attention to overwintering

Summary

Introduction

Cold hardiness and diapause are essential components of winter survival for most insects in temperate zones (Denlinger, 1991). In freeze-avoiding species, which survive in a supercooled state, low-molecular weight sugars and polyols including glycerol, sorbitol, mannitol, inositol and trehalose may accumulate as cryoprotective agents (reviewed in Sømme, 1982; Denlinger, 1991; Lee, 1991; Storey & Storey, 1991). The codling moth, Cydia pomonella, is a key pest of apple in various regions of Iran (Rajabi et al, 1978; Akrami, 1984; Saeb, 1994). This moth passes the winter as a full-grown diapausing larva within a thick, silken cocoon under loose bark on the trunks of apple trees. The codling moth has successfully followed the spread of apple cultivation and occurs in most apple production areas throughout the world (Barnes, 1991; Dorn et al, 1999) inhabiting various climates, even where winter temperatures sometimes reach as low as –25°C (Newcomer, 1920; Yothers & Carlson, 1941; Geier, 1963; Sato, 1964; Hagley, 1970; Berankova et al, 1988)

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