# Endophytic Entomopathogenice Fungi: A Valuable Biological Control Tool against Plant Pests
## 1 Introduction  
Insect pests are responsible for a loss of 18-26% of worldwide annual crop production, which corresponds to an estimated value of $470 billion [1]. The greatest part of the losses (13-16%) occurs in the field, before harvest [1]. Furthermore, post-harvest pests constitute a major part of storage losses of agricultural products. About 50-60% of stored grains can be lost during the storage period due to insufficient control measures [2]. The intense use of chemicals has led to more than 500 species of arthropod pests becoming resistant to one or more insecticide classes [2]. Additionally, environmental and food regulations represent a barrier for the development of new insecticides, in terms of both time and cost. Approximately 140,000 insecticidal compounds need to be screened in order to find one successful compound that would be in line with the regulations, and it could take more than $250 million and 8-12 years before an insecticide is developed and registered [3]. Crop protection by agrochemicals has been responsible for maintaining and increasing the quality and quantity of crop production worldwide. However, their extensive and often irresponsible use has resulted in pest resistance, resurgence of secondary pests and a disruption or elimination of natural enemy complexes, thus reducing the efficacy of natural control processes. These factors, coupled with concerns about the impact on environment and human safety, have provided the momentum to develop more environmentally safe strategies that are both cost-effective and reliable. Integrated pest management (IPM) is a comprehensive approach to crop production, combining a broad array of compatible techniques such as sanitation, survey and detection, use of resistantvarieties, cultural manipulation, trap and companion cropping, and biological control, as well as agricultural chemicals when appropriate, in order to maintain pests below economic damage levels. This approach represents a shift from the traditional, individual, pest-centered strategies that rely heavily on chemical pesticides to a more holistic approach, viewing the crop production system as a whole for the management rather than eradication of pests [4; 5]. Among the non-chemical pest control methods, biological control by entomogenic microorganisms represents one of the most effective options [6; 7; 8; 9]. The use of entomogenic fungi (EPF) to reduce pest population density and, consequently, crop damage plays a key role in sustainable pest management programs. EPF have several advantages when compared with 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 human-managed ecosystems [10; 11; 12; 13]. However, only a few genera have been applied as entomogens, including Beauveria, Metarhizium, Isaria, Lecanicillium and Hirsutella. These are used in fungal-based products, which have been formulated for use against a wide range of pests in forest, field and greenhouse environments, as well as against structural, household and storage pests. Approximately 750 EPF species have been discovered to cause infection in a wide array of insects and mites, although individual fungal species and strains are very target specific [13]. Fungi act by producing spores that germinate and grow on the body of the insect host. Infection is initiated when spores attach to the insect integument, where the formation of the germinative tube and enzyme excretion begin. Penetration of the insect's cuticle is achieved not only by the mechanical pressure of a specialized structure formed in the germinative tube, the apresorium, but also by the action of degradative enzymes. Inside the insect haemocele, fungal hyphae are developed and invade tissues and organs. The timeframe of death (between 3 and 7 days) depends on the type of fungus and number of infecting spores.