Effects of Endophytic Entomopathogenic Ascomycetes on the Life-History Traits of Aphis gossypii Glover and Its Interactions with Melon Plants

Fungal Endophytes as Mitigators against Biotic and Abiotic Stresses in Crop Plants

The escalating global food demand driven by a gradually expanding human population necessitates strategies to improve agricultural productivity favorably and mitigate crop yield loss caused by various stressors (biotic and abiotic). Biotic stresses are caused by phytopathogens, pests, and nematodes, along with abiotic stresses like salt, heat, drought, and heavy metals, which pose serious risks to food security and agricultural productivity. Presently, the traditional methods relying on synthetic chemicals have led to ecological damage through unintended impacts on non-target organisms and the emergence of microbes that are resistant to them. Therefore, addressing these challenges is essential for economic, environmental, and public health concerns. The present review supports sustainable alternatives, emphasizing the possible application of fungal endophytes as innovative and eco-friendly tools in plant stress management. Fungal endophytes demonstrate capabilities for managing plants against biotic and abiotic stresses via the direct or indirect enhancement of plants' innate immunity. Moreover, they contribute to elevated photosynthesis rates, stimulate plant growth, facilitate nutrient mineralization, and produce bioactive compounds, hormones, and enzymes, ultimately improving overall productivity and plant stress resistance. In conclusion, harnessing the potentiality of fungal endophytes represents a promising approach toward the sustainability of agricultural practices, offering effective alternative solutions to reduce reliance on chemical treatments and address the challenges posed by biotic and abiotic stresses. This approach ensures long-term food security and promotes environmental health and economic viability in agriculture.

Endophytic fungi improved wheat resistance to Rhopalosiphum padi by decreasing its feeding efficiency and population fitness

The improvement of crop resistance to insect using endophytic fungi is an environmentally friendly and sustainable strategy for agricultural pest control. Clarifying the efficacy and mechanism of endophytic fungi in improving crop resistance to pest offers the opportunity for biological control. In this study, changes in the transcriptome and defense compounds of wheat inoculated with endophytic fungal strains (i.e., YC and BB) were evaluated, and the efficacy of endophytic fungi in improving wheat resistance to Rhopalosiphum padi was studied. The results showed that the numbers of upregulated differentially-expressed genes (DEGs) in wheat plants inoculated with endophytic fungal strains YC and BB were higher than those of the downregulated DEGs, irrespective of R. padi infestation. Defense-related metabolic pathways, such as plant hormone signal transduction and secondary metabolite biosynthesis pathways were significantly enriched. Endophytic fungal strains YC and BB significantly increased jasmonic acid, DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), total flavone, and tannin contents in wheat plants (P < 0.05) but decreased salicylic acid content. Variations in the contents of defense compounds were significantly correlated with decreased feeding, development, and reproduction of R. padi fed on wheat plants inoculated with strains YC and BB (|r| = 0.68-0.91, P < 0.05). The results suggested that endophytic fungi significantly decreased the feeding efficiency and population fitness [YC: (-11.13%) - (-22.07%); BB: (-10.98%) - (-22.20%)] of R. padi by altering the phytohormone pathway and secondary metabolite biosynthesis in wheat plants. This study helps in understanding of the efficacy of endophytic fungi in improving wheat resistance to insect and will be conducive to integrated pest management.

Endophytic insect pathogenic fungi-host plant-herbivore mutualism: elucidating the mechanisms involved in the tripartite interactions

Various techniques used by crop plants to evade insect pests and pathogen attacks have been documented. Among these, plant defense strategies induced by endophytic insect pathogenic fungi are arguably one of the most discussed. Endophytic fungi frequently colonize plants and inhabit their internal tissues for a portion of their lifespan without producing visible symptoms of the disease. This phenomenon is widespread and diverse in both natural and agricultural ecosystems, and is present in almost all plant organs. Many fungi can obtain nutrients by infecting and killing insects, and this ability has been developed numerous times in different fungal lineages. These species mainly consist of those in the order Hypocreales (Ascomycota), where the generalist insect pathogens, Beauveria sp. (Cordycipitaceae) and Metarhizium sp. (Clavicipitaceae) are two of the most studied endophytic entomopathogenic fungal genera. However, most fungi that kill insects do not survive in the tissues of living plants. The data published thus far show a high degree of variability and do not provide consistent explanations for the underlying mechanisms that may be responsible for these effects. This implies that available knowledge regarding the colonization of plant tissues by endophytic insect pathogenic fungi, the effects of colonization on plant metabolism, and how this contributes to a decrease in herbivore and pathogens damage is limited. To adequately utilize fungal-based products as biological control agents, these products must be effective and the reduction of pests and infection must be consistent and similar to that of chemical insecticides after application. This article discusses this possibility and highlights the benefits and the specific techniques utilized by endophytically challenged plants in invading insect pests and disease pathogens.

Entomopathogenic Fungus-Related Priming Defense Mechanisms in Cucurbits Impact Spodoptera littoralis (Boisduval) Fitness

Entomopathogenic fungi (EPF) exhibit direct and indirect mechanisms to increase plant resistance against biotic and abiotic stresses. Plant responses to these stresses are interconnected by common regulators such as ethylene (ET), which is involved in both iron (Fe) deficiency and induced systemic resistance responses. In this work, the roots of cucurbit seedlings were primed with Metarhizium brunneum (EAMa 01/58-Su strain), and relative expression levels of 18 genes related to ethylene (ET), jasmonic acid (JA), and salicylic acid (SA) synthesis, as well as pathogen-related (PR) protein genes, were studied by reverse transcription-quantitative PCR (qRT-PCR). Effects of priming on Spodoptera littoralis were studied by feeding larvae for 15 days with primed and control plants. Genes showed upregulation in studied species; however, the highest relative expression was observed in roots and shoots of plants with Fe deficiency, demonstrating the complexity and the overlapping degree of the regulatory network. EIN2 and EIN3 should be highlighted; both are key genes of the ET transduction pathway that enhanced their expression levels up to eight and four times, respectively, in shoots of primed cucumber. Also, JA and SA synthesis and PR genes showed significant upregulation during the observation period (e.g., the JA gene LOX1 increased 506 times). Survival and fitness of S. littoralis were affected with significant effects on mortality of larvae fed on primed plants versus controls, length of the larval stage, pupal weight, and the percentage of abnormal pupae. These results highlight the role of the EAMa 01/58-Su strain in the induction of resistance, which could be translated into direct benefits for plant development. IMPORTANCE Entomopathogenic fungi are multipurpose microorganisms with direct and indirect effects on insect pests. Also, EPF provide multiple benefits to plants by solubilizing minerals and facilitating nutrient acquisition. A very interesting and novel effect of these fungi is the enhancement of plant defense systems by inducing systematic and acquired resistance. However, little is known about this function. This study sheds light on the molecular mechanisms involved in cucurbits plants' defense activation after being primed by the EPF M. brunneum. Furthermore, the subsequent effects on the fitness of the lepidopteran pest S. littoralis are shown. In this regard, a significant upregulation was recorded for the genes that regulate JA, SA, and ET pathways. This increased expression of defense genes caused lethal and sublethal effects on S. littoralis. This could be considered an added value for the implementation of EPF in integrated pest management programs.

Biostimulant and Bioinsecticidal Effect of Coating Cotton Seeds with Endophytic Beauveria bassiana in Semi-Field Conditions

Increasing commercial demands from the textile and food industries are putting strong pressure on the cultivation of cotton and its derivatives to produce high yields. At the same time, cotton has high nutrient and irrigation requirements and is highly susceptible to insect pests. Coating cotton seeds with beneficial fungi could address these problems. The aim of this study was to investigate the growth of cotton using (A) conventional seeds and (B) seeds coated with the entomopathogenic fungus Beauveria bassiana (Hypocreales: Cordycipitaceae). The experiment was conducted in a greenhouse of the Department of Agriculture of the University of Ioannina, in a completely randomized design. The growth characteristics of cotton plants were recorded weekly while the fresh weight and dry matter of the leaves, shoots and roots of the developed cotton plants were calculated at the end of the experiment. Weekly determination of total chlorophyll content (TCHL) was used as an indicator of plant robustness during the 80-day experiment. Many cotton growth parameters of treated plants, like number of leaves, shoots and apical buds, plant height, stem diameter, fresh and dried biomass and TCHL, were significantly higher than those of the untreated ones. Apart from plant growth, naturally occurring by Aphis gossypii (Hemiptera: Aphididae) infestation which also monitored for six weeks. A significantly lower aphid population was recorded for inoculated plants after the fifth week compared to the control. The overall evaluation revealed that B. bassiana coating treatments appear to have a significant biostimulatory and bioinsecticidal effect. Our results could represent responsive applications to the demands of intensive cotton growing conditions.

Deciphering Plant-Insect-Microorganism Signals for Sustainable Crop Production

Agricultural crop productivity relies on the application of chemical pesticides to reduce pest and pathogen damage. However, chemical pesticides also pose a range of ecological, environmental and economic penalties. This includes the development of pesticide resistance by insect pests and pathogens, rendering pesticides less effective. Alternative sustainable crop protection tools should therefore be considered. Semiochemicals are signalling molecules produced by organisms, including plants, microbes, and animals, which cause behavioural or developmental changes in receiving organisms. Manipulating semiochemicals could provide a more sustainable approach to the management of insect pests and pathogens across crops. Here, we review the role of semiochemicals in the interaction between plants, insects and microbes, including examples of how they have been applied to agricultural systems. We highlight future research priorities to be considered for semiochemicals to be credible alternatives to the application of chemical pesticides.

Inoculation and colonization of the entomopathogenic fungi, Isaria javanica and Purpureocillium lilacinum, in tomato plants, and their effect on seedling growth, mortality and adult emergence of Bemisia tabaci (Gennadius)

Entomopathogenic fungi (EPF) are natural enemies which affect insect population and have long been recognized as biological control agents against many insect pests. Some isolates have also been established as endophytes, benefiting their host plants without causing any symptoms or negative effects. Here we demonstrated two entomopathogenic fungal species, Isariajavanica (Frieder. & Bally) Samson & Hywel-jone 2005 and Purpureocillium lilacinum (Thom) Luangsa-ard, Hou-braken, Hywel-Jones & Samson (2011) as endophytes in tomato plants by using the seed inoculation method and examined their effect on plant growth, B. tabaci mortality, and adult emergence. Our study indicated that tomato seeds treated with a fungal suspension of I. javanica and P. lilacinum enabled their recovery from plant tissues (root, stem and leaf) up to 60 days after inoculation (DAI). Both endophytic isolates also caused significant mortality of adult B. tabaci on seedlings inoculated with, I. javanica (51.92±4.78%), and P. lilacinum (45.32±0.20%) compared to the control treatment (19.29±2.35). Adult emergence rates were significantly high in the control treatments (57.50±2.66%) compared to I. javanica (15.00±1.47%) and P. lilacinum (28.75±4.78%) treatments. This study provides evidence that endophytic isolates of I. javanica and P. lilacinum have a biocontrol potentials for used against whiteflies and could also explored as plant growth promoters.

Combatting insects mediated biotic stress through plant associated endophytic entomopathogenic fungi in horticultural crops

Horticultural production is a vital catalyst for economic growth, yet insect infestations reduce horticultural crop yield and quality. Pesticides and other pest control methods are used during planting to eliminate pests that cause direct and indirect losses. In such situations, endophytic entomo-pathogenic fungi (EEPF) can act as a potential tools for biological control. They protect plants by boosting growth, nutrition, morpho-physiology and salt or iron tolerance. Antixenosis, antibiosis and plant tolerance change insect performance and preferences. EEPF- plant colonisation slows herbivore development, food consumption, oviposition and larval survival. EEPF changes plant physio-chemical properties like volatile emission profile and secondary metabolite production to regulate insect pest defences. EEPF produces chitinases, laccases, amylases, and cellulases for plant defence. Recent studies focused on EEPF species' significance, isolation, identification and field application. Realizing their full potential is difficult due to insufficient mass production, storage stability and formulation. Genetic-molecular and bioinformatics can help to build EEPF-based biological control systems. Metagenomics helps study microbial EEPF taxonomy and function. Multi-omics and system biology can decode EEPF interactions with host plants and microorganisms. NGS (Next Generation Sequencing), comparative genomics, proteomics, transcriptomics, metabolomics, metatranscriptomics and microarrays are used to evaluate plant-EEPF relationships. IPM requires understanding the abiotic and biotic elements that influence plant-EEPF interaction and the physiological mechanisms of EEPF colonisation. Due to restricted research, there are hundreds of unexplored EEPFs, providing an urgent need to uncover and analyse them.

Impact of endophytic colonization by entomopathogenic fungi on the behavior and life history of the tobacco peach aphid Myzus persicae var. nicotianae

Entomopathogenic fungi can adopt an endophytic lifestyle and provide protection against insect herbivores and plant pathogens. So far, most studies have focused on Beauveria bassiana to increase plant resistance against abiotic and biotic stresses, while only little is known for other entomopathogenic fungi. In this study, we investigated whether root inoculation of sweet pepper (Capsicum annuum L.) by the entomopathogenic fungi Akanthomyces muscarius ARSEF 5128 and B. bassiana ARSEF 3097 can improve resistance against the tobacco peach aphid Myzus persicae var. nicotianae. First, dual-choice experiments were performed to test the hypothesis that the fungi deter aphids via modifying plant volatile profiles. Next, we tested the hypothesis that endophytic colonization negatively affects aphid life history traits, such as fecundity, development and mortality rate. Aphids were significantly attracted to the odor of plants inoculated with A. muscarius over non-inoculated plants. Plants inoculated with A. muscarius emitted significantly higher amounts of β-pinene than non-inoculated plants, and significantly higher amounts of indole than B. bassiana-inoculated and non-inoculated plants. Inoculation with the fungal strains also caused significantly higher emission of terpinolene. Further, both aphid longevity and fecundity were significantly reduced by 18% and 10%, respectively, when feeding on plants inoculated with A. muscarius, although intrinsic rate of population increase did not differ between inoculated and non-inoculated plants. Sweet pepper plants inoculated with B. bassiana ARSEF 3097 did not elicit a significant behavioral response nor affected the investigated life history traits. We conclude that endophytic colonization by entomopathogenic fungi has the potential to alter olfactory behavior and performance of M. persicae var. nicotianae, but effects are small and depend on the fungal strain used.

Compatibility and synergistic interactions of fungi, Metarhizium anisopliae, and insecticide combinations against the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae)

Aphids are major pests affecting cereals, vegetables, fruit, forestry and horticultural produce. A multimodal approach may be an effective route to controlling this prolific pest. We assessed the individual and combined effect of eight insecticides and the entomopathogenic fungi, Metarhizium anisopliae (Metschin.) against the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), under laboratory conditions. Six of the insecticides tested were found to be highly compatible (flonicamid, imidacloprid, nitenpyram, dinotefuran, pyriproxyfen and spirotetramat), showing positive integration with the fungus and were selected for bioassays. The combination mixtures (1:1 ratio of M. anisopliae: insecticide) were significantly more toxic to A. gossypii than individual treatments. Maximum mortality (91.68%) of A. gossypii was recorded with combination of flonicamid and M. anisopliae (2.4 × 10⁶ cfu/ml) 72 h after application. While minimum mortality (17.08%) was observed with the individual treatment of M. anisopliae (2.4 × 10⁶ cfu/ml). The insecticides revealed toxicity consistent with their compatibility with M. anisopliae, ranking for efficacy exactly as they did for compatibility. In addition, the synergy factor (SF) and co-toxicity coefficient (CTC) values indicated synergistic interactions at different time intervals. The synergistic efficacy revealed the potential of fungus-insecticide integration against sucking insect pests.

Endophytic Colonization by the Entomopathogenic Fungus Beauveria Bassiana Affects Plant Volatile Emissions in the Presence or Absence of Chewing and Sap-Sucking Insects

Entomopathogenic fungi are gaining acceptance in Integrated Pest Management (IPM) systems as effective and environmental safety biological control agents to protect a great variety of crops against pest insects. Many of these insect-pathogenic fungi can establish themselves as endophytes and thereby may induce the plant immune system. The activation of plant defenses by the fungal endophytic colonization can have a direct impact on herbivores and plant pathogens. An integral component of many plant defense responses is also the release of volatile organic compounds, which may serve as an indirect defense by attracting the natural enemies of herbivores. Here we investigated the effect of endophytic colonization by the entomopathogenic fungus Beauveria bassiana on the volatile emission by melon and cotton plants, either unharmed or after being damaged by sap-sucking aphids or leaf chewing caterpillars. We found that when the plants are colonized by B. bassiana they emit a different blend of volatile compounds compared to uncolonized control plants. Some of the emitted compounds have been reported previously to be released in response to herbivory and have been implicated in natural enemy attraction. Several of the compounds are also known to have antimicrobial properties. Therefore, endophytic colonization by B. bassiana might help to not only direct control insect pests but also increase the resistance of plants against agronomically important pests and phytopathogens.

Pest management via endophytic colonization of tobacco seedlings by the insect fungal pathogen Beauveria bassiana

BACKGROUND

It has been suggested that entomopathogenic fungi can be introduced into plants as endophytes potentially leading to insect control. Here, we sought to identify specific strains of the insect pathogenic fungus, Beauveria bassiana that would form endophytic associations with tobacco (Nicotiana benthamiana) benefitting host plant growth and/or resistance against insect pests and pathogens.

RESULTS

Tobacco seeds were inoculated with six different B. bassiana strains and entophytic colonization, plant growth, and resistance to pathogens and insect pests were evaluated over a 50 day-period. Although all the strains could colonize seedlings, 90% seedling colonization was seen for four strains. Fungal cells could be detected in stems more readily than in leaf and root tissues. Colonization by B. bassiana boosted plant growth with an increased photosynthetic rate, chlorophyll content, and stomatal and trichome density seen in fungal treated plants. Tobacco seedlings colonized by specific B. bassiana strains displayed significantly increased tolerance/resistance against bacterial and fungal pathogens. B. bassiana-colonized seedlings also displayed higher resistance to aphids (Myzus persicae) as compared to untreated controls. Colonization by B. bassiana was shown to trigger both of the salicylic acid (SA) and jasmonate acid (JA) defense pathways, but SA pathway was upregulated much more than JA pathway for some of the tested strains.

CONCLUSION

Specific strains of B. bassiana can be introduced into host plants as endophytes, resulting in promotion of host plant growth, increased resistance to microbial pathogens, and/or increased resistance to insect pests. © 2020 Society of Chemical Industry.

Molecular insight into the endophytic growth of Beauveria bassiana within Phaseolus vulgaris in the presence or absence of Tetranychus urticae

Entomopathogenic fungi are an important factor in the natural regulation of arthropod populations. Moreover, some can exist as an endophyte in many plant species and establish a mutualistic relationship. In this study, we have investigated the endophytic growth of Beauveria bassiana within different tissues of Phaseolus vulgaris in the presence and absence of Tetranuychus urticae. After the colonization of the B. bassiana within the internal tissues of P. vulgaris. The susceptibility of T. urticae appeared to depend on the life stage where high, moderate, and low mortalities were recorded among adults, nymphs, and eggs, respectively. In addition, this study provided, for the first time, molecular insight into the endophytic growth of B. bassiana by analyzing the expression of several genes involved in the development of the entomopathogenic fungi at 0-, 2-, and 7- days post-inoculation. B. bassiana displayed preferential tissue colonization within P. vulgaris that can be put into the following order based on the detection rate: leaf > stem > root. After analyzing the development-implicated genes (degrading enzymes, sugar transporter, hydrophobins, cell wall synthesis, secondary metabolites, stress management), the most remarkable finding is the detection of behavioral change between parasitic and endophytic Beauveria during post-penetration events. This study elucidates the tri-trophic interaction between fungus-plant-herbivore.

Direct and Indirect Effect via Endophytism of Entomopathogenic Fungi on the Fitness of Myzus persicae and Its Ability to Spread PLRV on Tobacco

Simple Summary

Aphids are major crop pests that are feeding on plant sap and transmitting plant viruses, thus inducing high yield losses worldwide. As chemical pesticides are decreasingly used in plant protection, fungi that cause disease to insects (entomopathogenic fungi) are one of the promising alternatives. They are commonly applied by spraying plants to protect them against herbivores. When applied, some fungi penetrate and live within plant tissues, thus helping to internally protect from insect attacks and other plant diseases. The aim of our study was to assess the effects of entomopathogenic fungi (EPF) applied firstly by contact after insect direct spraying, secondly by endophytic plant inoculation, and thirdly by associated both methods assessing the green peach aphid performances. The impact of the presence of endophytic entomopathogenic fungi (EEPF) in plant tissues on virus transmission by aphids was also considered. We found that the EPF Beauveria bassiana killed the green peach aphid and reduced its fecundity regardless of the application method. On fungal-inoculated plants, there was also a high mortality of aphid nymphs and infection by the potato leafroll virus (PLRV) was delayed by about a week with the EEPF treatment compared to fungal-free plants. This study showed that spraying plant leaves with EPF not only has a direct insecticidal effect against insects but could also have beneficial side effects for the plant against viruses.

Abstract

Aphids are major crop pests that transmit more than half of all insect-vectored plant viruses responsible for high yield losses worldwide. Entomopathogenic fungi (EPF) are biological control agents mainly used by foliar application to control herbivores, including sap-sucking pests such as aphids. Their ability to colonize plant tissues and to interact with diverse plant pathogenic microorganisms have been reported. In our study, we evaluated the effectiveness of Beauveria bassiana ((Balsamo-Crivelli) Vuillemin) directly applied by contact or/and indirectly via endophytism in tobacco plants (Nicotiana tabacum L.) against the virus vector Myzus persicae (Sulzer) carrying the Potato leafroll virus (PLRV) or not. We found that both contact treatment and endophytic colonization of leaves significantly increased aphid mortality and decreased the fecundity rate when compared to control plants. In addition, on fungal-colonized leaves, viruliferous aphids were more negatively impacted than virus-free ones and nymph mortality was significantly higher than on fungal-free plants. Furthermore, we assessed PLRV transmission by M. persicae on tobacco plants inoculated with either B. bassiana or Metarhizium acridum ((Driver and Milner) JF Bischoff, Rehner, and Humber) as source or/and recipient plants. Myzus persicae was found to acquire and transmit PLRV regardless of the treatment. Nevertheless, the infection rate of endophytically colonized plants was lower at a seven-day incubation period and had increased to almost 100% after fifteen days. These results suggest that B. bassiana is effective against aphids, both by contact and via endophytism, and both B. bassiana and M. acridum delayed PLRV infection in tobacco.

Does the Infectious Status of Aphids Influence Their Preference Towards Healthy, Virus-Infected and Endophytically Colonized Plants?

Aphids (Hemiptera: Aphididae) cause significant damage and transmit viruses to various crop plants. We aimed to evaluate how the infectious status of aphids influences their interaction with potential hosts. Two aphid (Myzus persicae and Rhopalosiphum padi) and plant (Nicotiana tabacum and Triticum aestivum) species were used. The preferences of aphids towards healthy, virus-infected (Potato Leafroll Virus (PLRV) and Barley Yellow Dwarf virus (BYDV)), and endophytic entomopathogenic fungi (EEPF)-inoculated (Beauveria bassiana and Metarhizium acridum) plants were investigated in dual-choice tests. The headspace volatiles of the different plant modalities were also sampled and analyzed. Viruliferous and non-viruliferous aphids were more attracted to EEPF-inoculated plants compared to uninoculated plants. However, viruliferous aphids were more attracted to EEPF-inoculated plants compared to virus-infected plants, while non-viruliferous insects exhibited no preference. Fungal-inoculated plants released higher amounts of aldehydes (i.e., heptanal, octanal, nonanal and decanal) compared to other plants, which might explain why viruliferous and non-viruliferous aphids were more abundant in EEPF-inoculated plants. Our study provides an interesting research perspective on how EEPF are involved in behavior of virus vector, depending on the infectious status of the latter.

Delving into the Causes and Effects of Entomopathogenic Endophytic Metarhizium brunneum Foliar Application-Related Mortality in Spodoptera littoralis Larvae

The aim of the current study was to delve into the causes of mortality of Spodoptera littoralis larvae feeding on Metarhizium-colonized plants in the absence of fungal outgrowth on the cadavers as previous studies reported and to elucidate the possible indirect effects of this fungus-colonized diet. The effect was evaluated in experiments conducted using leaf discs of colonized plants and in planta using fungus-colonized whole plants. The mortality rates of larvae fed on Metarhizium-colonized melon leaves were 45.0% and 87.5%, and the average survival times were 6.6 and 3.1 days in experiments performed with discs and in planta, respectively. Notably, these mortality levels were not associated with observed apoptosis mediated by caspases 1, 3-7 and 8; thus, further investigation into the possible immune system reaction of the insect after the ingestion of colonized plants is required. The leaf consumption of S. littoralis larvae fed on melon-colonized leaves was lower than that on control plants in the disc experiments but not in experiments conducted in planta. In this regard, in experiments performed in planta, plant damage increased larval mortality in both fungally challenged and control larvae. There was also a meaningful effect of exposure to Metarhizium-colonized melon leaf discs on S. littoralis fitness, with significant reductions in 39.0% and 22.0% in female fecundity and egg fertility, respectively, detected in females emerging from pupae developing from larvae surviving exposure to colonized plant discs; all larvae died in the in planta experiments. Hence, the present work presents new findings revealing the high potential of endophytic entomopathogenic fungi to improve the outcome of foliar applications against chewing insects in the short, mid- and long term, by the reduction of the reproductive potential of surviving adults and reveals new insights into the development of bioassays with whole plants for more detailed evaluation of the impact of these fungi as endophytes used for plant protection.

Endophytic Entomopathogenic Fungi: A Valuable Biological Control Tool against Plant Pests

Among the non-chemical insect control methods, biological control is one of the most effective human and environmentally friendly alternatives. One of the main biological control methods is the application of entomopathogenic fungi (EPF). Today, biological crop protection with EPF plays a key role in projects for the sustainable management of insect pests. EPF have several advantages over conventional insecticides, including cost-effectiveness, high yield, absence of harmful side-effects for beneficial organisms, fewer chemical residues in the environment and increased biodiversity in ecosystems. Apart from direct application as contact bioinsecticides, EPF are able to colonize plants as endophytes acting not only as pest and disease control agents but also as plant growth promoters. The present paper presents an outline of the biocontrol potential of several EPF, which could be harnessed for the development of new integrated pest Management (IPM) strategies. Emphasis is given on benefits of endophytic EPF, on issues for practical application and in fields in need of further research. Our findings are discussed in the context of highlighting the value of entomopathogenic fungal endophytes as an integral part of pest management programs for the optimization of crop production.