Abstract
As a serious pest of wheat, the Sunn pest, Eurygaster integriceps Puton (Hem.: Scutelleridae), is prevalent in Iran. This pest belongs to univoltine species and tends to estivate and overwinter in high altitudes of nearby mountains as diapausing adults. The economic importance of the crop was attacked by this pest, i.e., wheat led the authors to study the physiological adaptations of these diapausing adults, that is, changes in the supercooling point (SCP), in the accumulation of cryoprotectants, and in the activities of the related enzymes in relation to diapause development. The mean SCP of the diapausing adults was found to be −8°C. The lowest SCP, i.e., approximately −11°C, was observed in the middle of diapause, October, when the highest cold hardiness was also interestingly recorded. This finding proposed that SCP depression could be a feasible cold-tolerance strategy for diapausing adults. The sugar content was high in the initiation and at the termination of diapause and was low during diapause maintenance. These sugar reserves were most likely utilized to be converted to glycogen and lipid during diapause maintenance as a survival strategy. The changes in the glycogen and lipid contents were inversely proportional to the changes in the total sugar content. The authors also found that the changes in the glycogen content were directly proportional to those in the low-molecular-weight carbohydrates (e.g., glycerol and trehalose) and in the diapause development. This finding underlined the role of the low-molecular-weight carbohydrates, such as the cryoprotectants, in enhancing the cold tolerance of the given insect. In this study, the diapause-associated changes in the activities of α-amylases and proteases were also investigated. The results showed that the enzyme activities were related to diapause development and cold-tolerance enhancement. The highest enzyme activity was observed in September. Since the overwintering adults of the Sunn pest could not tolerate temperatures below their SCPs, they were grouped in the freeze-intolerant species.
Highlights
The ambient temperature can directly affect different stages of the life cycle of insects, as an ectothermic group of animals, including growth, development, reproduction, survival, and distribution (Régnicre et al, 2012; Jaworski and Hilszczanski, 2014)
The cold hardiness of E. integriceps was investigated in the altitude of Ateshgah Karaj-Iran, the results of which demonstrated that supercooling point (SCP) varied from −12.9◦C to −6.7◦C
The range of SCP changes of E. integriceps was relatively low during diapause, and the mean SCP was the lowest in the phase of the diapause maintenance of the adults
Summary
The ambient temperature can directly affect different stages of the life cycle of insects, as an ectothermic group of animals, including growth, development, reproduction, survival, and distribution (Régnicre et al, 2012; Jaworski and Hilszczanski, 2014). The mechanism adopted by the insects to avoid adversities in the environment is known as diapause (specified arrest of development), during which temperature, photoperiod, and/or food quality encourage some pre-programmed physiological changes, leading to the suppression of metabolism, the enhancement of resistance to cellular stress, and the onset of dormancy in advance of unfavorable environmental conditions (Poelchau et al, 2013; Roncalli et al, 2018). Depending on the type of bond they form, namely, α or β, this group has two major enzymes, that is, αamylase and β-amylase Another hydrolase enzyme is proteases, catalyzing the hydrolysis of peptide linkages of proteins and releasing amino acids from protein. The SCP was taken as an abrupt temperature increase occurring with the release of the latent heat of crystallization (Mohammadzadeh and Izadi, 2016)
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