Fungus–plant interaction influences plant-feeding insects

Effect of the mycotoxins enniatin B and deoxynivalenol on the wheat aphid Sitobion avenae and on the predatory lacewing Chrysoperla carnea

BACKGROUND

Fusarium species are responsible for Fusarium head blight (FHB) in wheat, resulting in yield losses and mycotoxin contamination. Deoxynivalenol (DON) and enniatins (ENNs) are common mycotoxins produced by Fusarium, affecting plant, animal and human health. Although DON's effects have been widely studied, limited research has explored the impact of ENNs on insects. This study examines the influence of DON and enniatin B (ENB), both singularly and in combination, on the wheat aphid Sitobion avenae and one of its predators, the lacewing Chrysoperla carnea.

RESULTS

When exposed to DON (100 mg L-1) or DON + ENB (100 mg L-1), S. avenae exhibited significantly increased mortality compared to the negative control. ENB (100 mg L-1) had no significant effect on aphid mortality. DON-treated aphids showed increasing mortality from 48 to 96 h. A dose-response relationship with DON revealed significant cumulative mortality starting at 25 mg L-1. By contrast, C. carnea larvae exposed to mycotoxins via cuticular application did not show significant differences in mortality when mycotoxins were dissolved in water but exhibited increased mortality with acetone-solubilized DON + ENB (100 mg L-1). Feeding C. carnea with aphids exposed to mycotoxins (indirect exposure) did not impact their survival or predatory activity. Additionally, the impact of mycotoxins on C. carnea was observed only with acetone-solubilized DON + ENB.

CONCLUSIONS

These findings shed light on the complex interactions involving mycotoxins, aphids and their predators, offering valuable insights for integrated pest management strategies. Further research should explore broader ecological consequences of mycotoxin contamination in agroecosystems. © 2024 Society of Chemical Industry.

Penicillium-Infected Apples Benefit Larval Development of Conogethes punctiferalis via Alterations of Their Gut Bacteria Community and Gene Expression

Pathogenic microorganisms can impact the behavior and physiology of herbivores by direct or indirect means. This study demonstrated that yellow peach moth Conogethes punctiferalis larvae feeding on Penicillium-infected apples exhibited significantly longer body length and weight parameters compared to the control group. The sequencing of gut 16S rRNA showed a significant increase in the diversity and abundance of bacteria in the larvae feeding on Penicillium-infected apples. Additionally, transcriptomic sequencing of the larval gut indicated significant upregulation of genes related to digestion and cuticle formation after consuming Penicillium-infected apples. Furthermore, enzyme activity assays revealed notable changes in the trypsin and lipase activity. Consequently, these alterations in gut microbiota structure, diversity, and gene expression levels may underlie the observed growth and developmental variations in C. punctiferalis larvae mediated by pathogenic microorganisms. This study holds theoretical significance for a deeper understanding of the tripartite interaction among microorganisms, insects, and plants as well as for the development of novel pest control measures based on gut microbiota.

N-containing phenolic compounds from Periplaneta americana with triple negative breast cancer inhibitory activity

Eight previously undescribed compounds comprising pyrrole-2-carboxaldehyde derivatives, namely periplanpyrroles A-D (1-4), spirooxindole derivatives perispirooxindoles A (5) and B (6), and the phenolic compounds periplanetols G (7) and H (8), along with eight known compounds were isolated from the 70% ethanol extract of the whole bodies of Periplaneta americana. Their structures including absolute configurations were unambiguously identified by comprehensive spectroscopic analyses and computational methods. In addition, all compounds were evaluated for their activities against triple negative breast cancer in vitro. The wound healing assay revealed that 7, 9, and 11 significantly inhibit the migration of BT549 and MDA-MB-231 cells. Further observations made in Western blotting experiments showed that 7 could dose-dependently decrease the protein level of vimentin and N-cadherin in MDA-MB-231 and BT549 cells.

Mycobiomes of two distinct clades of ambrosia gall midges (Diptera: Cecidomyiidae) are species-specific in larvae but similar in nutritive mycelia

IMPORTANCE

Ambrosia gall midges are endophagous insect herbivores whose larvae live enclosed within a single gall for their entire development period. They may exhibit phytomycetophagy, a remarkable feeding mode that involves the consumption of plant biomass and mycelia of their cultivated gall symbionts. Thus, AGMs are ideal model organisms for studying the role of microorganisms in the evolution of host specificity in insects. However, compared to other fungus-farming insects, insect-fungus mutualism in AGMs has been neglected. Our study is the first to use DNA metabarcoding to characterize the complete mycobiome of the entire system of the gall-forming insects as we profiled gall surfaces, nutritive mycelia, and larvae. Interestingly, larval mycobiomes were significantly different from their nutritive mycelia, although Botryosphaeria dothidea dominated the nutritive mycelia, regardless of the evolutionary separation of the tribes studied. Therefore, we confirmed a long-time hypothesized paradigm for the important evolutionary association of this fungus with AGMs.

A life-and-death struggle: interaction of insects with entomopathogenic fungi across various infection stages

Insects constitute approximately 75% of the world's recognized fauna, with the majority of species considered as pests. Entomopathogenic fungi (EPF) are parasitic microorganisms capable of efficiently infecting insects, rendering them potent biopesticides. In response to infections, insects have evolved diverse defense mechanisms, prompting EPF to develop a variety of strategies to overcome or circumvent host defenses. While the interaction mechanisms between EPF and insects is well established, recent findings underscore that their interplay is more intricate than previously thought, especially evident across different stages of EPF infection. This review primarily focuses on the interplay between EPF and the insect defense strategies, centered around three infection stages: (1) Early infection stage: involving the pre-contact detection and avoidance behavior of EPF in insects, along with the induction of behavioral responses upon contact with the host cuticle; (2) Penetration and intra-hemolymph growth stage: involving the initiation of intricate cellular and humoral immune functions in insects, while symbiotic microbes can further contribute to host resistance; (3) Host insect's death stage: involving the ultimate confrontation between pathogens and insects. Infected insects strive to separate themselves from the healthy population, while pathogens rely on the infected insects to spread to new hosts. Also, we discuss a novel pest management strategy underlying the cooperation between EPF infection and disturbing the insect immune system. By enhancing our understanding of the intricate interplay between EPF and the insect, this review provides novel perspectives for EPF-mediated pest management and developing effective fungal insecticides.

VOCs from fungi-infected apples attract and increase the oviposition of yellow peach moth Conogethes punctiferalis

BACKGROUND

Plant volatile organic compounds (VOCs) modified by plant-associated microbes can attract or repel the oviposition of herbivores. Here, we explored the effects of three different fungi on apples' VOCs and the cascading impacts on the oviposition preference of yellow peach moth [YPM, Conogethes punctiferalis (Guenée)].

RESULTS

Among Penicillium crustosum-infected apples (PCA), Rhizopus oryzae-infected apples (ROA), Colletotrichum gloeosporioides-infected apples (CGA) and healthy apples (HA), mated YPM females preferred to oviposit eggs on ROA and CGA, and showed significant attractiveness to VOCs from PCA, ROA, and CGA under laboratory conditions. The VOCs analyses showed that there were significant differences between fungi-infected apples (ROA, CGA) and control treatments (mechanically damaged apples (MDA), HA) in terms of the relative contents of 13 VOCs. The relative contents of ethyl 2-methylbutyrate, ethyl caprylate, estragole, ethyl hexanoate in ROA and CGA were higher than those in MDA. The relative content of isopropyl 2-methylbutyrate in ROA was significantly higher than those in HA and CGA. The relative contents of 2-methylbutyl acetate, butyl 2-methylbutyrate, hexyl 2-methylbutyrate, amyl hexanoate, hexyl hexanoate, (E, E)-α-farnesene in ROA and CGA were lower than those in HA. The relative content of hexyl acetate in ROA and CGA was significantly higher than that in MDA, but lower than that in HA. Additionally, 10 fungi-induced VOCs were detected in ROA and/or CGA. When 20 VOCs from ROA and/or CGA were tested as individuals or mixed blends in Y-tube olfactometer assays, mated YPM females preferred amyl 2-methylbutyrate, isoamyl 2-methylbutyrate, isopropyl 2-methylbutyrate, hexyl propionate (common VOCs in ROA, CGA, and HA), and heptacosane (a fungi-induced VOC in ROA), but no significant preferences were observed between individual compounds and mixed blends, except for hexyl propionate.

CONCLUSION

Different fungi infection increased the relative contents of common VOCs from healthy and fungi-infected apples, which ultimately resulted in the significant attractiveness for the oviposition of mated YPM females. This study clarified why fungi-infected apples were more attractive to YPMs than healthy apples and screened out the crucial VOCs for YPM oviposition. © 2023 Society of Chemical Industry.

Linking Anthropogenic Landscape Perturbation to Herbivory and Pathogen Leaf Damage in Tropical Tree Communities

Anthropogenic disturbance of tropical humid forests leads to habitat loss, biodiversity decline, landscape fragmentation, altered nutrient cycling and carbon sequestration, soil erosion, pest/pathogen outbreaks, among others. Nevertheless, the impact of these alterations in multitrophic interactions, including host-pathogen and vector-pathogen dynamics, is still not well understood in wild plants. This study aimed to provide insights into the main drivers for the incidence of herbivory and plant pathogen damage, specifically, into how vegetation traits at the local and landscape scale modulate such interactions. For this purpose, in the tropical forest of Calakmul (Campeche, Mexico), we characterised the foliar damage caused by herbivores and pathogens in woody vegetation of 13 sampling sites representing a gradient of forest disturbance and fragmentation in an anthropogenic landscape from well preserved to highly disturbed and fragmented areas. We also evaluated how the incidence of such damage was modulated by the vegetation and landscape attributes. We found that the incidence of damage caused by larger, mobile, generalist herbivores, was more sensitive to changes in landscape configuration, while the incidence of damage caused by small and specialised herbivores with low dispersal capacity was more influenced by vegetation and landscape composition. In relation to pathogen symptoms, the herbivore-induced foliar damage seems to be the main factor related to their incidence, indicating the enormous importance of herbivorous insects in the modulation of disease dynamics across tropical vegetation, as they could be acting as vectors and/or facilitating the entry of pathogens by breaking the foliar tissue and the plant defensive barriers. The incidence of pathogen damage also responded to vegetation structure and landscape configuration; the incidence of anthracnose, black spot, and chlorosis, for example, were favoured in sites surrounded by smaller patches and a higher edge density, as well as those with a greater aggregation of semi-evergreen forest patches. Fungal pathogens were shown to be an important cause of foliar damage for many woody species. Our results indicate that an increasing transformation and fragmentation of the tropical forest of southern Mexico could reduce the degree of specialisation in plant-herbivore interactions and enhance the proliferation of generalist herbivores (chewers and scrapers) and of mobile leaf suckers, and consequently, the proliferation of some symptoms associated with fungal pathogens such as fungus black spots and anthracnose. The symptoms associated with viral and bacterial diseases and to nutrient deficiency, such as chlorosis, could also increase in the vegetation in fragmented landscapes with important consequences in the health and productivity of wild and cultivated plant species. This is a pioneering study evaluating the effect of disturbances on multitrophic interactions, offering key insights on the main drivers of the changes in herbivory interactions and incidence of plant pathogens in tropical forests.

“Lepidoptera Flies”, but Not Always…Interactions of Caterpillars and Chrysalis with Soil

Lepidoptera, an order of insects traditionally linked to the aerial habitat, are much more diverse in their living environment than the clichéd image we may have of them. The imago stage, which is the most visible in these insects, is not the one that has the most interaction with the environment (usually caterpillars) nor the one that lasts the longest (very often chrysalises). These two stages are often directly related to litter and soil, although only the interaction at the pupal stage seems to follow a phylogenetic logic with two independent evolutionary events for the preference with soil: Use of litter and the upper “O” horizon as protection against predation for the evolutionarily oldest Lepidoptera families, pupation at greater depths (up to 60 centimetres in extreme cases) for the most derived Lepidoptera families; this probably to take advantage of the thermal and moisture buffer provided by the soil. An estimate suggests that about 25% of lepidopteran species worldwide have more or less obligatory interactions with soil.

Penicillium fungi mediate behavioral responses of the yellow peach moth, Conogethes punctiferalis (Guenée) to apple fruits via altering the emissions of host plant VOCs

Plant-associated microbes have been reported as important but overlooked drivers of plant-herbivorous insect interactions. Influence of plant-associated microbes on plant-insect interactions is diverse, including beneficial, detrimental, and neutral. Here, we determined the effects of three Penicillium fungi, including Penicillium citrinum, Penicillium sumatrense, and Penicillium digitatum, on the oviposition selection and behavior of the yellow peach moth (YPM), Conogethes punctiferalis (Guenée). Compared with fungi noninfected apples (NIA), mechanically damaged apples (MDA), and P. citrinum in potato dextrose agar medium (PC), the oviposition selection and four-arm olfactometer experiments both showed that mated YPM females preferred to P. citrinum-infected apples (PCA). For P. sumatrense or P. digitatum, we also found that mated YPM females preferred to P. sumatrense-infected apples (PSA) or P. digitatum-infected apples (PDA), respectively. Among three Penicillium fungi-infected apples, the selection rates including oviposition and olfactometer behavior of mated YPM females on PDA were both higher than those on PSA and PCA. Further analyses of host plant volatile organic compounds (VOCs) by GC-MS showed that the absolute contents of ethyl hexanoate and (Z, E)-α-farnesene in PCA, PSA, and PDA were all higher than those in NIA, and a total of 16 novel VOCs were detected in fungi-infected apples (PCA, PSA, and PDA), indicating that fungi infection changed the components and proportions of apple VOCs. Taken together, three Penicillium fungi play significant roles in mediating the host selection of YPMs via altering the emissions of VOCs. These findings will be beneficial for developing formulations for field trapping of YPMs in the future.

Distinct cytological mechanisms for food availability in three Inga ingoides (Fabaceae)-Cecidomyiidae gall systems

Gall cytological, metabolic, and structural traits are established due to the feeding habits of the associated galling herbivores, and sometimes are influenced by other organisms involved in the interaction. We tested this assumption on three gall morphotypes, the globoid, the lenticular, and the fusiform, induced by Cecidomyiidae on leaflets of Inga ingoides (Rich.) Willd. (Fabaceae: Caesalpinioideae). Taking for granted that the three Cecidomyiidae galls are induced on the same host plant and organ, we assume that the cytological and histochemical traits of their nutritive cells may be similar, but under the fungi influence, the ambrosia gall cytological profile may be peculiar and reflect on the accumulation of primary metabolites. The ambrosia globoid galls involve three organisms (host plant, gall inducer, and fungi), while the fusiform and the lenticular galls involve two organisms (host plant and gall inducer). The accumulation of primary metabolites is similar among the three gall morphotypes, except for the non-detection of reducing sugars in the fusiform galls. The fungi presence can impact the system but does not define exclusive features for the ambrosia globoid galls when compared to the lenticular and fusiform morphotypes. In fact, the cytological traits have revealed three different cytological mechanisms for food resources availability to the three galling Cecidomyiidae: (a) cell wall destructuring and cell death by fungi intermediation in the ambrosia globoid galls, (b) necrosis-type cell death in the fusiform galls, and (c) maintenance of continuous metabolic activity in the lenticular galls.

Selection of Endophytic Beauveria bassiana as a Dual Biocontrol Agent of Tomato Pathogens and Pests

Endophytic fungi (EF) can enhance both plant growth and defense barriers against pests and pathogens, contributing to the reduction of chemical pesticides and fertilizers use in agriculture. Beauveria bassiana is an entomopathogenic fungus showing endophytism in several crops, often associated with a good capacity to limit the development of pests and disease agents. However, the diversity of the protective efficacy and plant response to different strains can be remarkable and needs to be carefully assessed for the successful and predictable use of these beneficial microorganisms. This study aims to select B. bassiana strains able to colonize tomato plants as endophytes as well as to control two important disease agents, Botrytis cinerea and Alternaria alternata, and the pest aphid, Macrosiphum euphorbiae. Nine wild-type isolates and one commercial strain were screened for endophytism, then further characterized for plant-growth promotion plus inhibition of disease development and pest infestation. Four isolates proved to have a good control activity against the biotic stressors tested, but only Bb716 was also able to promote plant growth. This work provides a simple workflow for the selection of beneficial EF, paving the way towards more effective use of B. bassiana in Integrate Pest Management (IPM) of tomato.

Seed Treatment With Systemic Fungicides: Time for Review

Pre-sowing seed treatment with systemic fungicides is a firmly entrenched practice for most agricultural crops worldwide. The treatment is intended to protect the crop against seed- and soil-borne diseases. In recent years, there is increasing evidence that fungicidal applications to manage diseases might inadvertently also affect non-target organisms, such as endophytes. Endophytes are ubiquitously present in plants and contribute to plant growth and development besides offering resistance to biotic and abiotic stresses. In seeds, endophytes may play a role in seed development, seed germination, seedling establishment and crop performance. In this paper, we review the recent literature on non-target effects of fungicidal applications on endophytic fungal community and discuss the possible consequences of indiscriminate seed treatment with systemic fungicide on seed endophytes. It is now well recognized that endophytes are ubiquitously present in all parts of the plant, including the seeds. They may be transmitted vertically from seed to seed as in many grasses and/or acquired horizontally from the soil and the environment. Though the origins and evolution of these organisms in plants are a matter of conjecture, numerous studies have shown that they symbiotically aid in plant growth and development, in nutrient acquisition as well in protecting the plants from abiotic and biotic stresses. Against this background, it is reasonable to assume that the use of systemic fungicides in seed treatment may not only affect the seed endophytes but also their attendant benefits to seedling growth and establishment. While there is evidence to indicate that fungicidal applications to manage plant diseases also affect foliar endophytes, there are only few studies that have documented the effect of seed treatment on seed-borne endophytes. Some of the convincing examples of the latter come from studies on the effect of fungicide application on rye grass seed endophyte AR37. More recently, experiments have shown that removal of seed endophytes by treatment with systemic fungicides leads to significant loss of seedling vigour and that such losses could be partially restored by enriching the seedlings with the lost endophytes. Put together, these studies reinforce the importance of seed endophytes to seedling growth and establishment and draw attention on how to trade the balance between the benefits of seed treatments and the direct and indirect costs incurred due to loss of endophytes. Among several approaches, use of reduced-risk fungicides and identifying fungicide-resistant endophytes are suggested to sustain the endophyte contribution to early seedling growth.

The Diversity and Dynamics of Fungi in Dryocosmus kuriphilus Community

Simple Summary

Dryocosmus kuriphilus is an invasive pest species which is native to China and is widely distributed in Asia, Europe and North America. D. kuriphilus induces insect galls on chestnut trees, and fungi can cause the necrosis of chestnut trees and the death of D. kuriphilus. The aim of this research was to investigate the potential role of D. kuriphilus in the transmission of fungi. We provide the first evidence that D. kuriphilus adults shared most fungal species with associated insect galls and the galled twigs of Castanea mollissima, and were dominated by Botryosphaeria sp., Aspergillus sp. and Diaporthe sp. Furthermore, we suggest that D. kuriphilus adults may be potential vectors of plant pathogens and mediate the transmission of fungi between chestnut trees.

Abstract

Dryocosmus kuriphilus (Hymenoptera: Cynipidae) is a gall wasp that induces insect galls on chestnut trees and results in massive yield losses worldwide. Fungi can cause the necrosis of chestnut trees and the death of gall wasps. The aim of this research was to investigate the potential role of D. kuriphilus in the transmission of fungi. We sequenced the ribosomal RNA internal transcribed spacer region 1 of fungi in D. kuriphilus adults, associated insect galls and the galled twigs of Castanea mollissima, using high-throughput sequencing. We compared the species richness, α-diversity and community structure of fungi in D. kuriphilus adults, insect galls and the galled twigs. We provide the first evidence that D. kuriphilus adults shared most fungal species with associated insect galls and the galled twigs, and were dominated by Botryosphaeria sp., Aspergillus sp. and Diaporthe sp. We suggest D. kuriphilus adults may be potential vectors of plant pathogens and may facilitate the transmission of fungi between chestnut trees. Furthermore, the fungi may horizontally transmit among D. kuriphilus adults, associated insect galls and the galled twigs.

Herbivore-induced rice resistance against rice blast mediated by salicylic acid

In agro-ecosystems, plants are important mediators of interactions between their associated herbivorous insects and microbes, and any change in plants induced by one species may lead to cascading effects on interactions with other species. Often, such effects are regulated by phytohormones such as jasmonic acid (JA) and salicylic acid (SA). Here, we investigated the tripartite interactions among rice plants, three insect herbivores (Chilo suppressalis, Cnaphalocrocis medinalis or Nilaparvata lugens), and the causal agent of rice blast disease, the fungus Magnaporthe oryzae. We found that pre-infestation of rice by C. suppressalis or N. lugens but not by C. medinalis conferred resistance to M. oryzae. For C. suppressalis and N. lugens, insect infestation without fungal inoculation induced the accumulation of both JA and SA in rice leaves. In contrast, infestation by C. medinalis increased JA levels but reduced SA levels. The exogenous application of SA but not of JA conferred resistance against M. oryzae. These results suggest that pre-infestation by C. suppressalis or N. lugens conferred resistance against M. oryzae by increasing SA accumulation. These findings enhance our understanding of the interactions among rice plant, insects and pathogens, and provide valuable information for developing an ecologically sound strategy for controlling rice blast.

Fungal Endophyte-Mediated Crop Improvement: The Way Ahead

Endophytes are non-disease causing microbes (bacteria and fungi) surviving in living tissues of plants. Their intimate association and possible coevolution with their plant partners have resulted in them contributing to an array of plant growth benefits ranging from enhanced growth and biomass accumulation, tolerance to abiotic and biotic stresses and in nutrient acquisition. The last couple of decades have witnessed a burgeoning literature on the role of endophytes (Class 3 type) in regulating plant growth and development and their adaptation to abiotic and biotic stresses. Though the underlying mechanisms of plant-endophyte interactions are far from clear, several studies have raised the hope of their potential application in agriculture, especially in mitigating abiotic and biotic stresses. The use of endophytes is envisaged as a route to reduce the production cost and burden on the environment by lessening the dependence on breeding for crop improvement and agrochemicals. Unfortunately, save a few well documented examples of their use, a little of these insights has been translated into actual agricultural applications. Here, we reflect on this paucity and elaborate on some of the important bottlenecks that might stand in way of fully realizing the potential that endophytes hold for crop improvement. We stress the need to study various facets of the endophyte-plant association for their gainful application in agriculture.

Dibutyl phthalate contamination remolded the fungal community in agro-environmental system

Dibutyl phthalate (DBP) is a typical soil contaminant that is widely used as plasticizer in modern agricultural production. In this study, an experiment was conducted to evaluate fungal community succession in a soil-vegetable ecosystem under different DBP concentrations. By using high-throughput sequencing of the ribosomal internal transcribed spacer (ITS) region, it was shown that DBP contamination caused significant changes to the soil fungal community, in terms of both α and β diversities. The largest changes in fungal α and β diversities were detected under 50 mg/kg DBP concentration at the first day of addition. The bulk soils, rhizosphere soils and the phyllosphere harbored different fungal communities, while the abundance of saprotrophs and plant pathogens in the phyllosphere have been increased under DBP contamination. From correlation analysis and partial Mantel test, the change in fungal community α diversity was the result of multiple factors (DBP concentration, bacterial community and soil properties) while the β diversity of fungal community was mainly co-varied with the bacterial community after DBP contamination. Moreover, molecular ecological network analysis demonstrated that DBP contamination was detrimental to mutualistic relationships among fungal species and destabilized the network structure. Overall, the fungal communities in soils and around vegetables were largely remolded by DBP contamination that provides new insight into DBP contamination impacts on agricultural ecosystems.