  Citation: Mantzoukas, S.; Kitsiou, F.; Natsiopoulos, D.; Eliopoulos, P.A. Entomopathogenic Fungi: Interactions and Applications. Encyclopedia 2022, 2, 646–656. https://doi.org/10.3390/ encyclopedia2020044 Academic Editors: Milva Pepi and Raffaele Barretta Received: 9 February 2022 Accepted: 20 March 2022 Published: 24 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Entry Entomopathogenic Fungi: Interactions and Applications Spiridon Mantzoukas 1, * , Foteini Kitsiou 1,2 , Dimitrios Natsiopoulos 2 and Panagiotis A. Eliopoulos 2, * 1 Department of Agriculture, University of Ioannina, 45100 Ioannina, Greece; kitsioufot@gmail.com 2 Lab of Plant Health Management, Department of Agrotechnology, University of Thessaly, 45100 Larissa, Greece; dimnatsiopoulos@uth.gr * Correspondence: sdmantzoukas1979@gmail.com (S.M.); eliopoulos@uth.gr (P.A.E.) Definition: Entomopathogenic fungi are a special group of soil-dwelling microorganisms that infects and kills insects and other arthropods through cuticle penetration. They are currently used as biocontrol agents against insect plant pests and play a vital role in their management. Regardless that entomopathogenic fungi are currently on the agriculture market, their full potential has not yet been utterly explored. Up to date substantial research has covered the topic revealing numerous uses in pest management but also on their ability as endophytes, assisting the plant host on growth and pathogen resistance. This article addresses the literature on entomopathogenic fungi through the years, noting their mode of action, advantages, potential applications, and prospects. Keywords: entomopathogenic fungi; insects; plants; endophytes; pest management; biopesticides 1. Introduction Interestingly, the idea of implementing microorganisms for pest control is not a modern application. The first entomopathogenic fungus was discovered and described by Agostino Bassi (1773–1856) in 1835, causing white muscardine disease in insects and was later named Beauveria bassiana (Balsamo) Vuillemin (Hypocreales, Cordycipitaceae) [1]. Some years later, Elias Metschnikoff (1845–1916) discovered the green muscardine, a fungal disease attacking insects, induced by Metarhizium anisopliae Metschnikoff Sorokin (Hypocreales, Clavicipitaceae) [2]. In the late 19th century, the combination of these discoveries and the groundbreaking knowledge obtained by the father of microbiology Louis Pasteur (1822–1895), led to assays experimenting on fungi as potential microbial control agents [3]. Later, the entrance of chemical insecticides in the market held back the establishment of fungi in pest management. Also, the development of Bacillus thuringiensis (Baciliales, Bacillaceae) Berliner against insects, played an important role on the biological protection research. While it assisted acknowledging the potential use of exploiting microorganisms as pest control agents, it may have detained the advance of biological protection studies, as the scientific community focused on bacterial entomopathogens [4]. Nonetheless, to present, even though entomopathogenic fungi (EPF) have been commercialized in the last years, their broad potential applications have not yet been fully discovered. The advances in molecular biology and DNA sequencing allowed the collection and classification of organisms and along with the symbiosis theory, provided a better com- prehension on the interactions between plants, fungi, and insects. During the last years, because of the concerning environmental implications of the extensive use of synthetic substances, the interests of research was rotated on alternatives of chemical pest man- agement and so the EPF came back on the scene. Up to date, numerous studies and reviews have documented the multifaceted roles of EPF as endophytes that antagonize plant diseases [5–10], promote plant growth [11–14], and benefit the rhizosphere through colonization [15–17]. The use of EPF so far has been limited to utilization as inundate biopesticides against insects [18], although the newly emerging attributes open the way to complementary roles as dual agents against both arthropods and plant diseases, as Encyclopedia 2022, 2, 646–656. https://doi.org/10.3390/encyclopedia2020044 https://www.mdpi.com/journal/encyclopedia