Cold hardiness in Ostrinia nubilalis (Lepidoptera: Pyralidae): Glycerol content, hexose monophosphate shunt activity, and antioxidative defense system

Bojana STANIC,Dusko P. BLAGOJEVIC,Aleksandra JOVANOVIC-GALOVIC,Gordana GRUBOR-LAJSIC,Roger WORLAND,Mihajlo B. SPASIC

doi:10.14411/eje.2004.065

Abstract

Many insects in temperate regions overwinter in diapause, during which they are cold hardy. In these insects, one of the metabolic adaptations to the unfavorable environmental conditions is the synthesis of cryoprotectants/anhydroprotectants. The aim of this study was to investigate the connection between the antioxidative system and synthesis of cryoprotectants (mainly glycerol) in diapausing larvae of the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae). At two periods during diapause (November and February), in three groups of insects (kept under field conditions; -12°C for two weeks; 8°C for two weeks), the activity of key enzymes of the antioxidative system and oxidative part of the hexose monophosphate shunt were measured: super- oxide dismutase, catalase, non selenium glutathione peroxidase, glutathione S-transferase, glutathione reductase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, as well that of the antioxidative components: total glutathione and ascorbate, and dehydroascorbate reductase. There was a higher activity of antioxidative enzymes at the beginning of the dia- pause period (November) compared to late diapause (February), while glutathione and ascorbate were higher in February. Similarly, there was a lower activity of the hexose monophosphate shunt enzymes in February. Exposure of larvae to -12°C resulted in an ele- vation of hexose monophosphate shunt enzyme activity, especially in November. This was accompanied by a significant increase in glycerol content in February. Changes in ascorbate levels and dehydroascorbate reductase activity in both experimental groups (-12°C and 8°C) suggest a connection between the antioxidative system, metabolism during diapause and cold hardiness. Our results support the notion that antioxidative defense in larvae of Ostrinia nubilalis is closely connected with metabolic changes character- istic of diapause, mechanisms of cold hardiness involved in diapause and the maintenance of a stable redox state.

Highlights

In insects that live in temperate climates cold tolerance and winter diapause are often closely linked in time, and survival mainly depends on physiological and biochemical changes that occur in response to low ambient temperatures
CAT data show that the activity of this enzyme in November increased in Ostrinia larvae kept at –12°C and 8°C, compared to those kept under field conditions
In November Glutathione reductase (GR) activity was significantly higher in control (8°C) and experimental (–12°C) Ostrinia larvae, when compared to those exposed to field conditions

Summary

Introduction

In insects that live in temperate climates cold tolerance and winter diapause are often closely linked in time, and survival mainly depends on physiological and biochemical changes that occur in response to low ambient temperatures. The early work of Chino (1957) on eggs of Bombyx mori suggested a link between diapause and the synthesis of the cryoprotectants glycerol and sorbitol from glycogen. A close correlation between diapause and the accumulation of cryoprotectants, such as polyhydric alcohols and trehalose, is reported for several insect species (Sømme, 1964, 1965; Asahina, 1966, Wyatt, 1969; Mansingh & Smallman, 1972; Lee et al, 1987). In some other diapausing species, which undergo winter hardening, accumulation of cryoprotective compounds is not connected directly to diapause (Baust & Miller, 1970; Wood & Nordin, 1976; Nordin et al, 1984)

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