Overwintering biology and limits of cold tolerance in larvae of pistachio twig borer, Kermania pistaciella

Glycerol Metabolism is Important for the Low-Temperature Adaptation of a Global Quarantine Pest Anoplophora glabripennis Larvae

Anoplophora glabripennis is a critical global quarantine pest. Recently, its distribution has been extended to colder and higher-latitude regions. The adaptation to low temperatures is vital for the successful colonization of insects in new environments. However, the metabolic pathways of A. glabripennis larvae under cold stress remain undefined. This study analyzed the larval hemolymph under different low-temperature treatments using LC-MS/MS. The results showed that differential metabolites associated with sugar and lipid metabolism are pivotal in the larval chill coma process. Under low-temperature treatments, the glycerol content increased significantly compared with the control group. Cold stress significantly induced the expression of AglaGK2 and AglaGPDHs. After undergoing RNAi treatment for 48 h, larvae exposed to -20 °C for 1 h showed reduced recovery when injected with ds-AglaGK2 and ds-AglaGPDH1 compared to the control group, indicating that glycerol biosynthesis plays a role in the low-temperature adaptation of A. glabripennis larvae. Our results provide a theoretical basis for clarifying the molecular mechanism of A. glabripennis larvae in response to environmental stresses.

Unveiling winter survival strategies: physiological and metabolic responses to cold stress of Monochamus saltuarius larvae during overwintering

BACKGROUND

Monochamus saltuarius is a destructive trunk-borer of pine forest and an effective dispersal vector for pinewood nematode (PWN), a causative agent of pine wilt disease (PWD), which leads to major ecological disasters. Cold winter temperatures determine insect survival and distribution. However, little is known about the cold tolerance and potential physiological mechanisms of M. saltuarius.

RESULTS

We demonstrated that dead Pinus koraiensis trunks do not provide larvae with insulation. The M. saltuarius larvae are freeze-tolerant species. Unlike most other freeze-tolerant insects, they can actively freeze extracellular fluid at higher subzero temperatures by increasing their supercooling points. The main energy sources for larvae overwintering are glycogen and the mid-late switch to lipid. The water balance showed a decrease in free and an increase in bound water of small magnitude. Cold stress promoted lipid peroxidation, thus activating the antioxidant system to prevent cold-induced oxidative damage. We found eight main pathways linked to cold stress and 39 important metabolites, ten of which are cryoprotectants, including maltose, UDP-glucose, d-fructose 6P, galactinol, dulcitol, inositol, sorbitol, l-methionine, sarcosine, and d-proline. The M. saltuarius larvae engage in a dual respiration process involving both anaerobic and aerobic pathways when their bodily fluids freeze. Cysteine and methionine metabolism, as well as alanine, aspartate, and glutamate metabolism, are the most important pathways linked to antioxidation and energy production.

CONCLUSIONS

The implications of our findings may help strengthen and supplement the management strategies for monitoring, quarantine, and control of this pest, thereby contributing to controlling the further spread of PWD. © 2024 Society of Chemical Industry.

Rhizoglyphus robini, a pest mite of saffron, is unable to resist extracellular ice formation

The saffron mite, Rhizoglyphus robini Claparède (Acari, Astigmata: Acaridae), is one of the most important pests of saffron-producing regions in Iran. It causes yellowing and decreases saffron growth, and finally it destroys the bulbs. In this research, the cold tolerance and supercooling point (SCP) of the saffron mite were measured in three populations and two temperature regimes. Our results showed that the mean SCP of the saffron mite was approximately -14.6 °C without significant difference among the populations. On the contrary, acclimation of the mites significantly decreased their SCP to a mean of approximately -16.5 °C. Exposure of the mites for 24 h to 0 and -2.5 °C had no significant effect on the survival of the mites but when the mites were exposed to -5.0 °C for 24 h, survival of the three populations reached the lowest level of roughly 60%. By 24-h exposure to -7.5 °C, survival of the mites was almost negligible. As a large proportion of mortality was observed above the SCP, and LT50 > SCP, it can be inferred that the saffron mite is likely a chill-susceptible species. This suggests that the saffron mite lacks the ability to withstand extracellular ice formation. Overall, the results of the current study suggest no significant physiological differences between populations of the saffron mite.

Physiological and biochemical differences in diapause and non-diapause pupae of Sericinus montelus (Lepidoptera: Papilionidae)

The swallowtail butterfly, Sericinus montelus Gray, is endemic to East Asia, has high ornamental value but faces an increased risk of extinction. To understand the overwintering strategies of this species, the dynamic changes in supercooling point (SCP) and water and biochemical contents of diapause-destined and non-diapause S. montelus pupae were investigated. The SCP of laboratory-reared diapause pupae was as low as -26°C compared to -24°C in diapause pupae in the field. Although there was no significant difference in total water content between diapause-destined and non-diapause pupae, the free water of diapause-destined pupae was significantly lower, and the bound water was significantly higher, than that of non-diapause pupae. Lipid, glycogen, and protein contents of diapause-destined pupae showed a downward trend, whereas the total sugar content showed the opposite trend after pupation. The glycogen content decreased rapidly during the initial stage of pupation, whereas the lipid content decreased significantly after 30 days of pupation, suggesting that diapause-destined pupae deplete glycogen stores during the pre-diapause period and then switch to using lipids during the diapause maintenance phase. Trehalose levels in diapause-destined pupae increased significantly and remained high after pupation. Meanwhile, the trehalose content of overwintering pupae during the diapause maintenance period was significantly higher than that of diapause termination pupae in the field. These results suggest that trehalose is the main cryoprotectant for overwintering pupae. Thus, diapausing S. montelus pupae appear to be freeze avoidant, accumulate trehalose as a cryoprotectant, and reduce the free water content to decrease the SCP, enhancing their cold tolerance.

Metabolic Response of Aphid Cinara tujafilina to Cold Stress

Climate changes enable thermophilic insect species to expand their ranges, but also force them to adapt to unfavourable environmental conditions in new habitats. Focusing on Cinara tujafilina, we investigated the metabolic changes in the body of the aphid that enabled it to survive the low temperatures of winter. Using GC–MS analysis, differences in the chemical composition of the aphids in summer and winter were found. The metabolic changes were mainly related to the increased activity of the pathways of carbohydrate metabolism, such as glycolysis and the pentose phosphate pathway; a decrease in tricarboxylic acid cycle (TCA); accumulation of polyols; and increased levels of proline, tyrosine, and fatty acids.

Expanded Supercooling Capacity With No Cryoprotectant Accumulation Underlies Cold Tolerance of the European Grapevine Moth

The European grapevine moth, Lobesia botrana (Denis et Schiffermuller), is a serious invasive pest that causes significant losses to the flowers and fruits of grapes in most of the world. This multivoltine pest passes the winter as the third-generation diapausing pupa. The current study was designed to compare nondiapausing (first and second generations) and diapausing pupae (third generation) and to investigate the relationship among cold tolerance, the supercooling point (SCP), and diapause development of the third-generation diapausing pupae. The lethal temperatures (LTs) for the three generations were determined using 24-h exposure at subzero temperatures. The mean SCP of the pupae was estimated at approx. -22.6°C, the lowest level of which (-23.7°C) was recorded in the well-developed diapausing pupae in February. The highest level of cold tolerance was also recorded in February. There were no significant differences among the temperatures required to kill 30, 50, and 90% of the pupae. The temperatures significantly decreased from October onward and reached the lowest levels in February during which the lowest SCP and the highest cold tolerance were observed in the diapausing pupae. No significant differences were found in the cryoprotectant levels, among the diapausing and nondiapausing pupae, and the diapause development. The highest activity of cAMP-dependent protein kinase (AMPK) was recorded in the late diapause in February. The findings suggested a relationship among SCP depression, cold tolerance enhancement, and diapause development. A bimodal cold-tolerance strategy (freeze-intolerant and freeze-tolerant) was found to be a feature of the pupae.

Simultaneous Occurrence of Diapause and Cold Hardiness in Overwintering Eggs of the Apple Oystershell Scale, Lepidosaphes Malicola Borchsenius (Hem.: Diaspididae)

As the key pest of apple fruits, the oystershell scale, Lepidosaphes malicola Borchsenius (Hem.: Diaspididae), overwinters as diapausing eggs under the protective, waxy cover of females. In this research, the effects of diapause development, cold acclimation, and rapid cold hardening were studied on the cold hardiness of the eggs. The changes in some physiological components were also investigated. The results indicated cold exposure to be a prerequisite for the survival of the diapausing eggs of L. malicola. No eggs hatched without exposure to cold. In addition, a direct relationship was observed among cold hardiness, cold acclimation, and diapause of the eggs based on the results. The highest level of hatching (the highest cold hardiness) of the eggs (80%) occurred in the cold-acclimated eggs at the end of diapause (March). Rapid cold hardening also influenced the cold hardiness of the eggs with diapause development. At the end of diapause, the lowest (61%) and the highest (77%) rates of egg survival were observed when the eggs were exposed to 5 and -10°C for 24 h, respectively. Cold hardiness of the diapausing eggs of L. malicola was also accompanied by some physiological changes, i.e., a decrease in glycogen content and an increase in simple sugar, lipid, and protein contents. The lowest glycogen content (about 50 μg/g) and the highest amounts of total simple sugars (454 μg/g) of lipids (542 μg/g) and proteins (84 μg/g) were observed in the cold-acclimated eggs at the end of diapause.

Overwintering Physiology and Cold Tolerance of the Sunn Pest, Eurygaster integriceps, an Emphasis on the Role of Cryoprotectants

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.

Cold tolerance and supercooling points of two ladybird beetles (Col.: Coccinellidae): Impact of the diet

Ladybird beetles have successfully been used to control different pests. Cheilomenes sexmaculata (Fabricius) and Oenopia conglobata contaminata)Menetries((Coleoptera: Coccinellidae) are two dominant and efficient predators of the common pistachio psylla, Agonoscena pistaciae (Hem.: Psyllidae) in Iran. In the current study, the impact of two diets, i.e., nymphs of A. pistaciae and eggs of Ephestia kuehniella Zeller (Lep.: Pyralidae), were investigated on the cold hardiness, supercooling point (SCP), and lethal temperature of different life stages of the coccinellids. The results suggested that the eggs of E. kuehniella are a suitable diet for both predators. In general, beetles of O. conglobata contaminata were more cold tolerant than those of C. sexmaculata. The SCP of the adults of C. sexmaculata, feeding on psyllid was about -15 °C, whereas the SCP of the beetles, feeding on the eggs of flour moth, was about -19 °C. However, the diets had no significant effects on the SCP of O. conglobata contaminata. For both ladybird beetles, eggs were the most sensitive stage, and adulthood was the most tolerant developmental stage. No eggs survived at zero and subzero temperatures. The survival of C. sexmaculata increased from 6.25% for adults fed on psyllids to 13.75% for those fed on flour moth eggs after 24 h exposure to cold at -4 °C. The survival of O. conglobata contaminata adults after exposure to cold at -4 °C for 24 h raised from 28.75% for adults fed on psyllids to 42.50% for those fed on flour moth eggs. Regardless of the diet, both beetles were considered to be chill-intolerant insects as the most mortality occurred above the SCP.