（Entomopathogenic fungi）
（Li Yunwei）
Fungi that parasitize insects and make them pathogenic. They are a type of lower eukaryotic organisms that cannot perform photosynthesis and rely on other animals and plants to provide nutrients. They have no roots, stems, or leaves. They live nutritionally with filamentous hyphae and conidia, blastospores, and arthrospores. (in body fluids) to reproduce. In terms of classification status, it belongs to the fungus phylum of the kingdom Fungi. So far, 36 genera and more than 500 species have been found to have control significance, accounting for about 60% of insect pathogens. The main ones are Sculptomyces, Streptochytrium, Entomophthora, Helicobacterium, Aspergillus, Beauveria, Metarhizium, Stachybotrys, Paecilomyces, Polychaeta, Erythora, Verticillium, Cephalosporium, Fusarium and Fusarium. Among them, the most commonly used entomophilic fungi for biological control include Beauveria bassiana, Metarhizium anisopliae, Paecilomyces spp., Polytrichum, Erythropodium erythroplasty, Entomophthora spp., etc.
Pathogenic mechanism
Entomopathogenic fungi generally contact the insect body through conidia, germinate under conditions of water droplets or high humidity of more than 90%, and secrete chitinase , dissolved chitin invades the body cavity of the pest; or the conidia are brought into the digestive tract by the pest, germinate in the digestive tract, grow into hyphae, and penetrate the intestinal wall cells into the body cavity. After the mycelium enters the insect body, it first breeds blastospores in large numbers in the insect's blood, or breaks off directly to form many arthrospores. Then the spores spread throughout the body with the blood flow, continue to germinate and grow into a large number of hyphae, and invade blood cells, fat bodies, digestive tracts, and horses. Organ tissue cells such as ducts, ganglia, trachea, etc. gradually cloud the blood, destroy cells, and produce a large amount of oosporine to poison and kill the insects. At the same time, a large amount of water from the insect body is absorbed during the growth of mycelium, causing the insect to die and gradually hardening. In a humid environment, mycelium penetrates the body wall, grows on the body surface, and finally forms a large number of conidia, which are blown away by the wind and fall on healthy insects. If conditions are favorable, new infections are often formed. Cause insect epidemics.
Production and Utilization
People take advantage of the pathogenic characteristics of entomophilous fungi and through years of experimental research, they have summarized a set of methods of isolation culture, mass production, and artificial release of bacteria. And used to control a variety of agricultural and forestry pests. China has successfully used indoor large bed open culture (solid shallow tray fermentation) and outdoor ground (sand bed) open culture (seedbed fermentation) methods to mass-produce 5 to 10 billion/g Beauveria bassiana powder and 120 to 150 billion Beauveria bassiana powder. /g of pure spore powder. At the same time, methods such as dusting, spraying, powder cannons, applying live insects in the field, or using ultra-low-volume aircraft to spray pure spore oils and emulsions have been used to control pine caterpillars, corn borers, wood moths, camellia camellia moths, and camphor leaf There are more than 20 kinds of insect pests, including beetles, small green leafhoppers, walnut long-legged elephants, nanmu shoot weevils, elm blue leaf beetles, elm green hornworms, poplar leafhoppers, pine poisonous moths, pine sawflies, and rice leafhoppers. There is a commercial preparation of Beauveria bassiana in the Soviet Union, with the trade name "Беаивепе" and a spore content of 2 to 6 billion/g. Beauveria bassiana powder produced in Romania contains 40 to 50 billion spores/g. France has approved a patent for Beauveria bassiana blastospores. Brazil and Australia have developed methods for large-scale production of Metarhizium anisopliae. The preparation is named "Metaquio" and is widely used in the control of underground pests such as scarab beetles. The United States has studied the industrial production of Polychaeta and Entomophora. Through more than 30 years of research on mycotoxins, the world has basically figured out the structural formula of Beauveria bassiana oosporine toxin. Its molecular formula is C45H57N3O7 (the synthesis of this toxin was reported in 1977), and it was further found that this toxin has both It has insecticidal effect and can also make adult insects lay eggs and be infertile.
The influence of environment on the pathogenicity of entomopathogenic fungi
The effect of applying fungi to control pests is closely related to the temperature and humidity conditions of the environment. The germination and infection of pathogen spores requires high humidity conditions of more than 95% (preferably more than 12 to 20 hours of water droplet coverage); after the pests become infected and die, they generally need a high humidity environment to promote the growth of mycelium. A large number of spores develop on the body surface to produce spores. Then, once the spores mature, drier and windier conditions are needed to facilitate the spread of the spores. Therefore, after artificial release of bacteria, if the weather alternates between sunny and rainy, and the forest stand is dry and wet, it is easy to form a pest epidemic, and achieve better control effects and economic benefits. Many fungi have a wide adaptability range to temperature, generally 20 to 30°C. For example, Beauveria bassiana can grow normally in the range of 8 to 31°C.
Strong direct sunlight will quickly kill a large number of spores. Other environmental factors such as wind, soil, humus, litter, and ground cover can also affect the persistence, spread, and infection of pathogenic spores. Therefore, how to study the application of entomopathogenic fungi from an ecosystem perspective is an important issue.