Ecological and Molecular Interactions between Insects and Fungi

Talarmalnoids A-F: Fusicoccane diterpenoids from an arthropod-derived endophytic fungus Talaromyces malicola

The metabolites from the endophytic fungus Talaromyces malicola hosted in the gastrointestinal tract of the arthropods Armadillidium vulgare were investigated, and six undescribed fusicoccane diterpenoids, talarmalnoids A-F (1-6), along with three known analogs were isolated. Talarmalnoid C (3) was an unprecedented fusicoccane diterpenoid with two sugar units, i.e., 6-O-methyl-α-d-glucose and α-d-glucose. Talarmalnoids D and E (4 and 5) were fusicoccane-type diterpenoids with unusual seven-membered rings attached at the C-3' and C-4' positions. Their structures and absolute configurations were identified by NMR, HRESIMS analyses, X-ray single crystal diffraction, GC-MS, ECD analyses, 13C NMR calculations, and DP4+ probability analyses. Bioassay results showed that talarmalnoid B (2) exhibited significant inhibitory activities against the LPS-inducted production of NO in RAW 264.7 cells, with IC50 value of 0.83 μM.

Microbial Volatile Organic Compounds: Insights into Plant Defense

Volatile organic compounds (VOCs) are low molecular weight molecules that tend to evaporate easily at room temperature because of their low boiling points. VOCs are emitted by all organisms; therefore, inter- and intra-kingdom interactions have been established, which are fundamental to the structuring of life on our planet. One of the most studied interactions through VOCs is between microorganism VOCs (mVOCs) and plants, including those of agricultural interest. The mVOC interactions generate various advantages for plants, ranging from promoting growth to the activation of defense pathways triggered by salicylic acid (systemic acquired resistance) and jasmonic acid (induced systemic resistance) to protect them against phytopathogens. Additionally, mVOCs directly inhibit the growth of phytopathogens, thereby providing indirect protection to plants. Among the current agricultural problems is the extensive use of chemicals, such as fertilizers, intended to combat production loss, and pesticides to combat phytopathogen infection. This causes problems in food safety and environmental pollution. Therefore, to overcome this problem, it is important to identify alternatives that do not generate environmental impacts, such as the application of mVOCs. This review addresses the protective effects of mVOCs emitted by microorganisms from different kingdoms and their implications in plant defense pathways.

Cladosporium-Insect Relationships

The range of interactions between Cladosporium, a ubiquitous fungal genus, and insects, a class including about 60% of the animal species, is extremely diverse. The broad case history of antagonism and mutualism connecting Cladosporium and insects is reviewed in this paper based on the examination of the available literature. Certain strains establish direct interactions with pests or beneficial insects or indirectly influence them through their endophytic development in plants. Entomopathogenicity is often connected to the production of toxic secondary metabolites, although there is a case where these compounds have been reported to favor pollinator attraction, suggesting an important role in angiosperm reproduction. Other relationships include mycophagy, which, on the other hand, may reflect an ecological advantage for these extremely adaptable fungi using insects as carriers for spreading in the environment. Several Cladosporium species colonize insect structures, such as galleries of ambrosia beetles, leaf rolls of attelabid weevils and galls formed by cecidomyid midges, playing a still uncertain symbiotic role. Finally, the occurrence of Cladosporium in the gut of several insect species has intriguing implications for pest management, also considering that some strains have proven to be able to degrade insecticides. These interactions especially deserve further investigation to understand the impact of these fungi on pest control measures and strategies to preserve beneficial insects.

Anti-Insect Properties of Penicillium Secondary Metabolites

In connection with their widespread occurrence in diverse environments and ecosystems, fungi in the genus Penicillium are commonly found in association with insects. In addition to some cases possibly implying a mutualistic relationship, this symbiotic interaction has mainly been investigated to verify the entomopathogenic potential in light of its possible exploitation in ecofriendly strategies for pest control. This perspective relies on the assumption that entomopathogenicity is often mediated by fungal products and that Penicillium species are renowned producers of bioactive secondary metabolites. Indeed, a remarkable number of new compounds have been identified and characterized from these fungi in past decades, the properties and possible applications of which in insect pest management are reviewed in this paper.

Interactions between Entomopathogenic Fungi and Insects and Prospects with Glycans

Concerns regarding the ecological and health risks posed by synthetic insecticides have instigated the exploration of alternative methods for controlling insects, such as entomopathogenic fungi (EPF) as biocontrol agents. Therefore, this review discusses their use as a potential alternative to chemical insecticides and especially focuses on the two major ones, Beauveria bassiana and Metarhizium anisopliae, as examples. First, this review exemplifies how B. bassiana- and M. anisopliae-based biopesticides are used in the world. Then, we discuss the mechanism of action by which EPF interacts with insects, focusing on the penetration of the cuticle and the subsequent death of the host. The interactions between EPF and the insect microbiome, as well as the enhancement of the insect immune response, are also summarized. Finally, this review presents recent research that N-glycans may play a role in eliciting an immune response in insects, resulting in the increased expression of immune-related genes and smaller peritrophic matrix pores, reducing insect midgut permeability. Overall, this paper provides an overview of the EPF in insect control and highlights the latest developments relating to the interaction between fungi and insect immunity.

Impact of green antioxidants on decreasing the aflatoxins percentage in peanut oil seed (Arachis hypogaea L.) during storage

The present study conducted an experimental investigation to impede the degradation of peanut (Arachis hypogaea L.) seeds and enhance their quality while being stored. The efficacy of eco-friendly chemicals such as ascorbic acid, salicylic acid, acetic acid, and propionic acid in seed preservation was evaluated over a period of six months. After a period of six months of storage in a greenhouse, an examination was conducted on peanut seeds that had undergone treatment. Rhizoctonia was observed after Cephalothorax, whereas Aspergillus, Fusarium, and Penicillium were the prevailing fungi throughout the storage period. The optimal outcomes were obtained from the conversion of acetic acid to propionic acid. The study observed a decline in seed oil, protein, carbohydrates, germination percentage, energy, index, length, vigour index, dead and rotten seeds, rotted seedlings, and surviving healthy seedlings, with an increase in storage duration ranging from zero to six months. The application of 100% propionic acid to peanut seeds throughout the storage duration resulted in decreased occurrences of deceased seeds, decaying seeds, and deteriorated seedlings. Peanut seeds that underwent treatment with green chemical agents of moderate and high intensity were found to be free of aflatoxin B1. The highest levels of chlorophylls a and b, carotenoids, and total phenols were observed in seeds stored in greenhouses and treated with 100% propionic acid and acetic acid extract. The application of propionic acid 100%, acetic acid 100%, salicylic acid 4 g/l and ascorbic acid 4 g/l proved to be the most effective treatments for peanut seeds, exhibiting the lowest total aflatoxin level of 0.40. The correlation coefficient between shoot fresh weight and shoot dry weight was found to be 0.99, whereas the correlation coefficient between root dry weight and shoot length was 0.67. The seed chemical analysis, seedling characteristics, and germination characteristics were subjected to clustering analysis, resulting in the formation of two distinct groups. The first group consisted of germination percentage and energy levels across all time points (0-6 months), while the second group consisted of the remaining characteristics. The findings of this research propose the utilisation of 100% propionic acid as a viable method for preserving peanut seeds and preventing their deterioration during storage. The application of 100% acetic acid has been found to be effective in enhancing the quality of seeds and minimising losses.

The Phytopathogen Fusarium verticillioides Modifies the Intestinal Morphology of the Sugarcane Borer

Background: In tropical sugarcane crops, the fungus Fusarium verticillioides, the agent responsible for the occurrence of the red rot complex, occurs in association with the sugarcane borer Diatraea saccharalis. This fungus, in addition to being transmitted vertically, can manipulate both the insect and the plant for its own dissemination in the field. Due to the complex interaction between F. verticillioides and D. saccharalis, and the high incidence of the fungus in the intestinal region, our objective was to investigate whether F. verticillioides could alter the intestinal structure of the insect. Methods: We combined analysis of scanning electron microscopy and light microscopy to identify whether the presence of the fungus F. verticillioides, in artificial diets or in sugarcane, could lead to any alteration or regional preference in the insect’s intestinal ultrastructure over the course of its development, or its offspring development, analyzing the wall and microvillous structures of the mid-digestive system. Results: Here, we show that the fungus F. verticillioides alters the intestinal morphology of D. saccharalis, promoting an increase of up to 3.3 times in the thickness of the midgut compared to the control. We also observed that the phytopathogen colonizes the intestinal microvilli for reproduction, suggesting that this region can be considered the gateway of the fungus to the insect’s reproductive organs. In addition, the colonization of this region promoted the elongation of microvillous structures by up to 180% compared to the control, leading to an increase in the area used for colonization. We also used the fungus Colletotrichum falcatum in the tests, and it did not differ from the control in any test, showing that this interaction is specific between D. saccharalis and F. verticillioides. Conclusions: The phytopathogenic host F. verticillioides alters the intestinal morphology of the vector insect in favor of its colonization.

"Ectomosphere": Insects and Microorganism Interactions

This study focuses on interacting with insects and their ectosymbiont (lato sensu) microorganisms for environmentally safe plant production and protection. Some cases help compare ectosymbiont microorganisms that are insect-borne, -driven, or -spread relevant to endosymbionts' behaviour. Ectosymbiotic bacteria can interact with insects by allowing them to improve the value of their pabula. In addition, some bacteria are essential for creating ecological niches that can host the development of pests. Insect-borne plant pathogens include bacteria, viruses, and fungi. These pathogens interact with their vectors to enhance reciprocal fitness. Knowing vector-phoront interaction could considerably increase chances for outbreak management, notably when sustained by quarantine vector ectosymbiont pathogens, such as the actual Xylella fastidiosa Mediterranean invasion episode. Insect pathogenic viruses have a close evolutionary relationship with their hosts, also being highly specific and obligate parasites. Sixteen virus families have been reported to infect insects and may be involved in the biological control of specific pests, including some economic weevils. Insects and fungi are among the most widespread organisms in nature and interact with each other, establishing symbiotic relationships ranging from mutualism to antagonism. The associations can influence the extent to which interacting organisms can exert their effects on plants and the proper management practices. Sustainable pest management also relies on entomopathogenic fungi; research on these species starts from their isolation from insect carcasses, followed by identification using conventional light or electron microscopy techniques. Thanks to the development of omics sciences, it is possible to identify entomopathogenic fungi with evolutionary histories that are less-shared with the target insect and can be proposed as pest antagonists. Many interesting omics can help detect the presence of entomopathogens in different natural matrices, such as soil or plants. The same techniques will help localize ectosymbionts, localization of recesses, or specialized morphological adaptation, greatly supporting the robust interpretation of the symbiont role. The manipulation and modulation of ectosymbionts could be a more promising way to counteract pests and borne pathogens, mitigating the impact of formulates and reducing food insecurity due to the lesser impact of direct damage and diseases. The promise has a preventive intent for more manageable and broader implications for pests, comparing what we can obtain using simpler, less-specific techniques and a less comprehensive approach to Integrated Pest Management (IPM).

Larvae of an invasive scarab increase greenhouse gas emissions from soils and recruit gut mycobiota involved in C and N transformations

Background

Soil-derived prokaryotic gut communities of the Japanese beetle Popillia japonica Newman (JB) larval gut include heterotrophic, ammonia-oxidizing, and methanogenic microbes potentially capable of promoting greenhouse gas (GHG) emissions. However, no research has directly explored GHG emissions or the eukaryotic microbiota associated with the larval gut of this invasive species. In particular, fungi are frequently associated with the insect gut where they produce digestive enzymes and aid in nutrient acquisition. Using a series of laboratory and field experiments, this study aimed to (1) assess the impact of JB larvae on soil GHG emissions; (2) characterize gut mycobiota associated with these larvae; and (3) examine how soil biological and physicochemical characteristics influence variation in both GHG emissions and the composition of larval gut mycobiota.

Methods

Manipulative laboratory experiments consisted of microcosms containing increasing densities of JB larvae alone or in clean (uninfested) soil. Field experiments included 10 locations across Indiana and Wisconsin where gas samples from soils, as well as JB and their associated soil were collected to analyze soil GHG emissions, and mycobiota (ITS survey), respectively.

Results

In laboratory trials, emission rates of CO₂, CH₄, and N₂O from infested soil were ≥ 6.3× higher per larva than emissions from JB larvae alone whereas CO₂ emission rates from soils previously infested by JB larvae were 1.3× higher than emissions from JB larvae alone. In the field, JB larval density was a significant predictor of CO₂ emissions from infested soils, and both CO₂ and CH₄ emissions were higher in previously infested soils. We found that geographic location had the greatest influence on variation in larval gut mycobiota, although the effects of compartment (i.e., soil, midgut and hindgut) were also significant. There was substantial overlap in the composition and prevalence of the core fungal mycobiota across compartments with prominent fungal taxa being associated with cellulose degradation and prokaryotic methane production/consumption. Soil physicochemical characteristics such as organic matter, cation exchange capacity, sand, and water holding capacity, were also correlated with both soil GHG emission, and fungal a-diversity within the JB larval gut. Conclusions: Results indicate JB larvae promote GHG emissions from the soil directly through metabolic activities, and indirectly by creating soil conditions that favor GHG-associated microbial activity. Fungal communities associated with the JB larval gut are primarily influenced by adaptation to local soils, with many prominent members of that consortium potentially contributing to C and N transformations capable of influencing GHG emissions from infested soil.

Molecular and Morphological Characteristics of a New Species Collected from an Insect (Cicindela transbaicalica) in Korea

To exploit insect-derived fungi, insects were collected from seven different regions in Korea, including Gyeongbuk, Goryeong, and several fungi were isolated from them. A fungal strain designated 21-64-D was isolated from riparian tiger beetle (Cicindela transbaicalica) and morphologically identified as a species belonging to the genus Oidiodendron. Phylogenetic analysis using the nucleotide sequences of internal transcribed spacer (ITS) regions and the partial sequence of the large subunit of the nuclear ribosomal RNA (LSU) gene revealed the distinct phylogenetic position of the isolate among recognized Oidiodendron species including its closest neighbors O. chlamydosporicum, O. citrinum, O. maius, and O. pilicola. The hyphal and conidial morphology of the strain, particularly club-shaped hyphae, clearly differentiated it from its close relatives. Results indicated that 21-64-D is a novel species in the genus Oidiodendron, for which the name Oidiodendron clavatum sp. nov. is proposed.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.

Molecular Detection and Differentiation of Arthropod, Fungal, Protozoan, Bacterial and Viral Pathogens of Honeybees

The honeybee Apis mellifera is highly appreciated worldwide because of its products, but also as it is a pollinator of crops and wild plants. The beehive is vulnerable to infections due to arthropods, fungi, protozoa, bacteria and/or viruses that manage to by-pass the individual and social immune mechanisms of bees. Due to the close proximity of bees in the beehive and their foraging habits, infections easily spread within and between beehives. Moreover, international trade of bees has caused the global spread of infections, several of which result in significant losses for apiculture. Only in a few cases can infections be diagnosed with the naked eye, by direct observation of the pathogen in the case of some arthropods, or by pathogen-associated distinctive traits. Development of molecular methods based on the amplification and analysis of one or more genes or genomic segments has brought significant progress to the study of bee pathogens, allowing for: (i) the precise and sensitive identification of the infectious agent; (ii) the analysis of co-infections; (iii) the description of novel species; (iv) associations between geno- and pheno-types and (v) population structure studies. Sequencing of bee pathogen genomes has allowed for the identification of new molecular targets and the development of specific genotypification strategies.