Effect of Cold Acclimation on Selected Metabolic Enzymes During Diapause in The European Corn Borer Ostrinia nubilalis (Hbn.)

Management of inorganic elements by overwintering physiology of cold hardy larvae of European corn borer (Ostrinia nubilalis, Hbn.)

The European corn borer (Ostrinia nubilalis, Hbn.), enters diapause, a strategy characterized by arrest of development and reproduction, reduction of metabolic rate and the emergence of increased resistance to challenging seasonal conditions as low sub-zero winter temperatures. The aim of this study was to investigate the potential role of inorganic elements in the ecophysiology of O. nubilalis, analysing their content in the whole body, hemolymph and fat body, both metabolically active, non-diapausing and overwintering diapausing larvae by ICP-OES spectrometer following the US EPA method 200.7:2001. O nubilalis as many phytophagous lepidopteran species maintain a very low extracellular sodium concentration and has potassium as dominant cation in hemolymph of their larvae. Changes in hemolymph and the whole body sodium content occur already at the onset of diapause (when the mean environmental temperatures are still high above 0 ºC) and remain stable during the time course of diapause when larvae of this species cope with sub-zero temperatures, it seems that sodium content regulation is rather a part of diapausing program than the direct effect of exposure to low temperatures. Compared to non-diapausing O. nubilalis larvae, potassium levels are much higher in the whole body and fat body of diapausing larvae and substantially increase approaching the end of diapause. The concentration of Ca, Mg, P and S differed in the whole body, hemolymph and fat body between non-diapausing and diapausing larvae without a unique trend during diapause, except an increase in their contents at the end of diapause.

Diapause-induced shift in the content of major carbohydrates in Chilo partellus (Swinhoe)

Although several aspects like diapause determining factors, population structure, reproductive physiology, and genetics of diapause have been investigated, there is no clarity on carbohydrate energetics during larval diapause in Chilo partellus (Swinhoe). Present studies revealed significant variation between the nondiapausing and diapausing C. partellus for total carbohydrates, glycogen, sorbitol, and trehalose contents in different body parts, life stages, and for body parts × life stages interaction. Total carbohydrate content started declining, while sorbitol and trehalose increased in all the body parts as the C. partellus larvae progressed from prediapausing to diapausing state. However, glycogen content spiked in all the body parts at prediapausing stage, which then declined during diapause. Among the body parts, total carbohydrate content was significantly greater in the hemolymph as compared to other body parts of both larvae and pupae of C. partellus. Glycogen content was significantly greater in the larval fat bodies and pupal hemolymph as compared to their other body parts. In diapausing larvae, sorbitol and trehalose were greater in the integument than in other body parts. Furthermore, there was spike in trehalose and decrease in sorbitol in all the body parts of pupae from diapausing than those from nondiapausing larvae. These findings suggest that the diapause alterate and/or fluctuate major carbohydrates in different body parts of both larvae and pupae of C. partellus. This information will be helpful in better understanding the diapause energetics and overwintering metabolic cryoprotection in insects.

De novo genome assembly of the invasive mosquito species Aedes japonicus and Aedes koreicus

BACKGROUND

Recently, two invasive Aedes mosquito species, Ae. japonicus and Ae. koreicus, are circulating in several European countries posing potential health risks to humans and animals. Vector control is the main option to prevent mosquito-borne diseases, and an accurate genome sequence of these mosquitoes is essential to better understand their biology and to develop effective control strategies.

METHODS

A de novo genome assembly of Ae. japonicus (Ajap1) and Ae. koreicus (Akor1) has been produced based on a hybrid approach that combines Oxford Nanopore long-read and Illumina short-read data. Their quality was ascertained using various metrics. Masking of repetitive elements, gene prediction and functional annotation was performed.

RESULTS

Sequence analysis revealed a very high presence of repetitive DNA and, among others, thermal adaptation genes and insecticide-resistance genes. Through the RNA-seq analysis of larvae and adults of Ae. koreicus and Ae. japonicus exposed to different temperatures, we also identified genes showing a differential temperature-dependent activation.

CONCLUSIONS

The assembly of Akor1 and Ajap1 genomes constitutes the first updated collective knowledge of the genomes of both mosquito species, providing the possibility of understanding key mechanisms of their biology such as the ability to adapt to harsh climates and to develop insecticide-resistance mechanisms.

European Corn Borer (Ostrinia nubilalis Hbn.) Bioecology in Eastern Romania

Between 2020 and 2021, we conducted research in eastern Romania to monitor the bioecology of the European corn borer (Ostrinia nubilalis Hbn.), an important pest of corn. The bioecology research established the pest stage duration (egg, larva, pupa, and moth), the flight curve, and the flight peak. The bioecological study occurred in the experimental corn field and a field cage. According to our findings, the insect has one generation per year. The European corn borer hibernates as a mature larva in corn residues and continues developing in the spring, when the weather warms. It pupates from May to July over 37 days. Analyzing the data recorded during the winters of 2020 and 2021, we observed that the warming trend favored the high survival of hibernating larvae (60.7%). Due to the large number of mature larvae that had favorable conditions during the winter, there is an intense flight, starting in June and ending in September. When the first moth was caught in the light trap, the ∑(tn-10) °C (sum of degree days) was 245.6 °C. In 2020, the flight was recorded for 94 days. In 2021, the European corn borer flight lasted 104 days. The initial egg masses were detected when the total of ∑(tn-10) °C reached 351.5 °C. Moths laid the eggs for 25 days, mostly during peak flight in late June and early July. The first larvae hatched when ∑(tn-10) °C totaled 438.4 °C, and stages III-V were recorded in the harvested crop. Understanding the bioecology of the European corn borer can offer valuable insights into managing population levels and identifying optimal timing for addressing infestations in corn crops.

Exposure to High Concentrations of Cadmium Which Delay Development of Ostrinia Nubilalis Hbn. Larvae Affected the Balance of Bioelements

All processes involved in metal homeostasis must be coordinated to provide sufficient, but not toxic, concentrations of important bioelements, and to minimize detrimental effects of toxic metals. Our previous studies dealing with the exposure of O. nubilalis non-diapausing larvae to dietary Cd demonstrated that exposure to higher concentrations of Cd caused delay in the development of larvae, induced oxidative stress and also induced defense mechanisms against the toxic effects of Cd. The aim of the present study was to evaluate how acute and chronic exposure of O. nubilalis larvae to increased concentrations of dietary Cd affected the balance of important bioelements. The concentration of bioelements was analyzed in larvae (after short-term exposure) and pupae (after long-term exposure). The short-term exposure of final instar larvae (L5) to Cd did not affect significantly the concentration of any of the analyzed bioelements, while the long-term exposure of developing larvae to higher concentrations of Cd caused increase in the concentrations of Ca, Mg and Na in pupae. The bioaccumulation factor, calculated for bioelements after long-term exposure to Cd, was higher for the most bioelements in groups fed with diet containing higher concentrations of Cd, except K which displayed the opposite trend. Pearson correlation coefficient showed positive correlations between Cd and Ca, Mg, Na, Fe, Cu and Zn, while negative correlation was observed between Cd and K. The results indicate that impact on the balance of important bioelements might be one of the mechanisms of cadmium toxicity and certainly raise numerous questions for future research.

Identification of Intrinsically Disordered Proteins and Regions in a Non-Model Insect Species Ostrinia nubilalis (Hbn.)

Research in previous decades has shown that intrinsically disordered proteins (IDPs) and regions in proteins (IDRs) are as ubiquitous as highly ordered proteins. Despite this, research on IDPs and IDRs still has many gaps left to fill. Here, we present an approach that combines wet lab methods with bioinformatics tools to identify and analyze intrinsically disordered proteins in a non-model insect species that is cold-hardy. Due to their known resilience to the effects of extreme temperatures, these proteins likely play important roles in this insect's adaptive mechanisms to sub-zero temperatures. The approach involves IDP enrichment by sample heating and double-digestion of proteins, followed by peptide and protein identification. Next, proteins are bioinformatically analyzed for disorder content, presence of long disordered regions, amino acid composition, and processes they are involved in. Finally, IDP detection is validated with an in-house 2D PAGE. In total, 608 unique proteins were identified, with 39 being mostly disordered, 100 partially disordered, 95 nearly ordered, and 374 ordered. One-third contain at least one long disordered segment. Functional information was available for only 90 proteins with intrinsic disorders out of 312 characterized proteins. Around half of the 90 proteins are cytoskeletal elements or involved in translational processes.

Cryoprotective Response as Part of the Adaptive Strategy of the Red Palm Weevil, Rhynchophorus ferrugineus, against Low Temperatures

Simple Summary

Low environmental temperature acts as a barrier that imposes limits on the geographic distribution of insects. However, due to Earth’s global warming, temperature might no longer be an impediment for insects to colonize some new areas. The spread of pest insects will depend on their adaptive response to cold periods and to thermal anomalies associated with climate change. In this study we analyzed whether the red palm weevil (RPW), one of the worst palm pests worldwide and native to warm areas, has physiological mechanisms that could configure an adaptive response to cold. We find that RPW is capable of rapidly producing substances that reduce chill injuries, primarily glucose as well as glycerol and several amino acids (mainly alanine). Therefore, this work shows for the first time that RPW is able to develop adaptive biochemical responses to deal with low temperatures, similar to those used by overwintering insects. Our results could be useful to improve models predicting the possible spread of RPW to new geographical areas, and also to try to prevent its adaptive response by disrupting the metabolic pathways regulating the involved substances.

Abstract

The red palm weevil (RPW), Rhynchophorus ferrugineus, is one of the worst palm pests worldwide. In this work, we studied the physiological basis underlying its adaptive strategy against low temperatures. Specifically, we analyzed the main low-molecular-weight biochemical substances acting as possible endogenous cryoprotectants, as well as their efficiency in reducing cold injury by preserving K⁺/Na⁺ homeostasis. Wild pre-pupae were cold-treated (5.0 ± 0.5 °C) or non-treated (23 ± 1 °C) for 7 days. We then determined the levels of: (a) glucose, trehalose and glycerol, spectrophotometrically, (b) amino acids, by liquid chromatography and (c) potassium and sodium, by inductively coupled plasma mass-spectrometry. Cold-treated larvae increased their potassium level, suggesting some degree of chill injury. However, part of the cold-exposed animals was able to develop an efficient overall cryoprotective response which primarily includes glucose, as well as glycerol and several amino acids (mainly alanine). Our study shows for the first time that RPW is capable of deploying effective physiological mechanisms for a rapid response to cold, which could be relevant to improving predictive models of geographic distribution, especially in a context of climate change. The knowledge of the specific molecules involved would allow future studies to try to prevent its adaptive strategy, either by natural or chemical methods.

Acclimations to Cold and Warm Conditions Differently Affect the Energy Metabolism of Diapausing Larvae of the European Corn Borer Ostrinia nubilalis (Hbn.)

The European corn borer Ostrinia nubilalis is a pest species, whose fifth instar larvae gradually develop cold hardiness during diapause. The physiological changes underlying diapause progression and cold hardiness development are still insufficiently understood in insects. Here, we follow a complex of changes related to energy metabolism during cold acclimation (5°C) of diapausing larvae and compare this to warm-acclimated (22°C) and non-diapause controls. Capillary electrophoresis of nucleotides and coenzymes has shown that in gradually cold-acclimated groups concentrations of ATP/ADP and, consequently, energy charge slowly decrease during diapause, while the concentration of AMP increases, especially in the first months of diapause. Also, the activity of cytochrome c oxidase (COX), as well as the concentrations of NAD+ and GMP, decline in cold-acclimated groups, until the latter part of diapause, when they recover. Relative expression of NADH dehydrogenase (nd1), coenzyme Q-cytochrome c reductase (uqcr), COX, ATP synthase (atp), ADP/ATP translocase (ant), and prohibitin 2 (phb2) is supressed in cold-acclimated larvae during the first months of diapause and gradually increases toward the termination of diapause. Contrary to this, NADP+ and UMP levels significantly increased in the first few months of diapause, after gradual cold acclimation, which is in connection with the biosynthesis of cryoprotective molecules, as well as regeneration of small antioxidants. Our findings evidence the existence of a cold-induced energy-saving program that facilitates long-term maintenance of larval diapause, as well as gradual development of cold hardiness. In contrast, warm acclimation induced faster depletion of ATP, ADP, UMP, NAD+, and NADP+, as well as higher activity of COX and generally higher expression of all energy-related genes in comparison to cold-acclimated larvae. Moreover, such unusually high metabolic activity, driven by high temperatures, lead to premature mortality in the warm-acclimated group after 2 months of diapause. Thus, our findings strongly support the importance of low temperature exposure in early diapause for gradual cold hardiness acquisition, successful maintenance of the resting state and return to active development. Moreover, they demonstrate potentially adverse effects of global climate changes and subsequent increase in winter temperatures on cold-adapted terrestrial organisms in temperate and subpolar regions.