Morphological response of the red palm weevil, Rhynchophorus ferrugineus, to a transient low temperature analyzed by computer tomography and holographic microscopy

Functional and evolutionary analysis of key enzymes triacylglycerol lipase, glycogen hydrolases in the glycerol and glucose biosynthesis pathway and cellular chaperones for freeze-tolerance of the Rice stem borer, Chilo suppressalis

Freeze-tolerance is an important physiological trait for terrestrial environmental adaptation and intraspecific geographic-lineage diversification in ectothermic animals, yet there remains a lack of systematic studies on its underlying genetic mechanisms and evolution. To address this problem, we employed the widely distributed rice pest, the Chilo suppressalis, as a model to explore the genetic mechanisms and evolutionary history of freeze-tolerance. First, we systematically characterized its antifreeze mechanisms by performing functional validation of potential key genes in laboratory-reared lines. This revealed the functional roles of glycerol biosynthesis in freeze-tolerance, including the triacylglycerol-originated pathway via triacylglycerol lipase (Tgl) hydrolysis and the glycogen-originated pathway via α-amylase (Aa) and maltase (Ma) hydrolysis, as well as the roles of the cellular chaperones Hsc70 and Hsf1. Then, we investigated the evolution of freeze-tolerance by collecting representative geographical samples and performing population genetic analyses, which suggested differentiated strategies of cold adaptation in different geographic populations. Taken together, our findings demonstrate the functional basis of cold resistance in Chilo suppressalis and reveal the evolutionary history of freeze-tolerance in natural populations, providing insights into organismal freeze-tolerance and clues for pest control.

Experimental evidence of a Neotropical pest insect moderately tolerant to complete freezing

Due to climate change, many regions are experiencing progressively milder winters. Consequently, pest insects from warm regions, particularly those with some tolerance to low temperatures, could expand their geographic range into these traditionally colder regions. The palm borer moth (Paysandisia archon) is a Neotropical insect that in recent decades has reached Europe and Asia as one of the worst pests of palm trees. Little is known about its ability to tolerate moderately cold winters and, therefore, to colonize new areas. In this work, we characterized the cold tolerance of Paysandisia archon by measuring its thermal limits: median lethal-temperature, LT50, chill-coma onset temperature, CTmin, supercooling point, SCP, freezing time and freezing survival. We found that this species was able to survive short periods of complete freezing, with survival rates of 87% after a 30-min freezing exposure, and 33% for a 1 h-exposure. It is then a moderately freeze-tolerant species, in contrast to all other lepidopterans native to warm areas, which are freeze-intolerant. Additionally, we investigated whether this insect improved its cold tolerance after either short or long pre-exposure to sub-lethal low temperatures. To that end, we studied potential changes in the main thermo-tolerance parameters and, using X-ray Computed Tomography, also in the morphological components of pretreated animals. We found that short pre-exposures did not imply significant changes in the SCP and CTmin values. In contrast, larvae with long pretreatments improved their survival to both freezing and low temperatures, and required longer times for complete freezing than the other groups. These long-term pre-exposed larvae also presented several morphological changes, including a reduction in water content that probably explained, at least in part, their longer freezing time and higher freezing survival. Our results represent the first cold tolerance characterization of this pest insect, which could be relevant to better design strategies to combat it.

Morphological and biochemical responses of a neotropical pest insect to low temperatures

As traditionally cold areas become warmer due to climate change, temperature could no longer be a barrier to the establishment of non-native insects. This is particularly relevant for pest insects from warm and tropical areas, mainly those with some tolerance to moderately low temperatures, which could expand their range into these new locations. From this perspective, in this work we studied the morphological and biochemical responses of the Neotropical pest Paysandisia archon to low temperatures, as part of a possible strategy to colonize new areas. To that end, wild larvae were exposed for 7 days to either low (1 and 5 °C) or ambient (23 °C) temperatures. We then quantified the inner and outer morphological changes, by X-Ray Computer Tomography and Digital Holographic Microscopy, as well as the accumulation of metabolites acting as potential endogenous cryoprotectants, by Spectrophotometry. We found that Paysandisia archon developed a cold-induced response based on different aspects. On the one hand, morphological changes occurred with a significant reduction both in fluids susceptible to freezing and fat body, together with the thickening, hardening and increased roughness of the integument. On the other hand, we found an increase in the hemolymph concentration of cryoprotective substances such as glucose (6-fold) and glycerol (2-fold), while trehalose remained unchanged. Surprisingly, this species did not show any evidence of cold-induced response unless the environmental temperature was remarkably low (1 °C). These results could be useful to improve models predicting the possible spread of such a pest, which should incorporate parameters related to its resistance to low temperatures.

Rhynchophorus ferrugineus larvae: A novel source for combating broad-spectrum bacterial and fungal infections

Antimicrobial resistance is a growing concern due to the growth of antibiotic-resistant microorganisms, which makes it difficult to treat infection. Due to its broad-spectrum antimicrobial properties against a diverse array of bacteria, both Gram-positive and Gram-negative bacteria, and fungi, Rhynchophorus ferrugineus larval antimicrobial peptides (AMPs) have demonstrated potential as antimicrobial agents for the treatment of microbial infections and prevention of antibiotic resistance. This study emphasizes the unexplored mechanisms of action of R. ferrugineus larvae against microorganisms. Among the most widely discussed mechanisms is the effect of AMPs in larvae in response to a threat or infection. Modulation of immune-related genes in the intestine and phagocytic capacity of its hemocytes may also affect the antimicrobial activity of R. ferrugineus larvae, with an increase in phenoloxidase activity possibly correlated with microbial clearance and survival rates of larvae. The safety and toxicity of R. ferrugineus larvae extracts, as well as their long-term efficacy, are also addressed in this paper. The implications of future research are explored in this paper, and it is certain that R. ferrugineus larvae have the potential to be developed as a broad-spectrum antimicrobial agent with proper investigation.

Sustainable Pest Management in Date Palm Ecosystems: Unveiling the Ecological Dynamics of Red Palm Weevil (Coleoptera: Curculionidae) Infestations

The red palm weevil (RPW) poses a significant threat to date palm ecosystems, highlighting the necessity of sustainable pest management strategies that carefully consider the delicate ecological balance within these environments. This comprehensive review delves into innovative approaches to sustainable pest management, specifically focusing on date palm, and seeks to unravel the intricate ecological dynamics underlying RPW infestations. We thoroughly analyze biocontrol methods, eco-friendly chemical interventions, and integrated pest management (IPM) strategies, aiming to minimize the ecological impact while effectively addressing RPW infestations. By emphasizing the interplay of both living organisms (biotic) and environmental factors (abiotic) in shaping RPW dynamics, we advocate for a holistic and sustainable management approach that ensures the long-term resilience of date palm ecosystems. This review aims to contribute to an ecologically sound framework for pest management, promoting the sustainability and vitality of date palm ecosystems amidst the challenges posed by the RPW.

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.