What do fungi and insects have in common

There are many different strains of the fungus that exhibit considerable variation in virulence, pathogenicity and host range. It occurs in the soil as a saprophyte. Metarhizium spp. It has a very broad host range and is extensively used in Brazil against spittle bugs in sugar cane and alfalfa. Other species of insect-pathogenic fungi have been tested as microbial insecticides for the control of pests.

Verticillium lecanii is used in Europe against greenhouse whitefly and thrips and aphids, especially in greenhouse crops. Neozygites floridana has been successfully tested against spider mites, and Nomuraea rileyi has activity against green cloverworm, cabbage looper, imported cabbageworm, armyworms, corn earworm, and tobacco budworm. Hirsutella thompsonii infects mites and was previously registered for use in the United States.

Hoffmann, M. Mahr, S. Midwest Biological Control News , 4 Tanada, Y. Academic Press, Inc. Weinzierl, R. Cooperative Extension, University of Illinois, Circular Top: Root maggot flies infected with fungus often die in an upright position on weeds or grasses. Photo: A. Frodsham Middle: Aphid killed by fungus.

Photo: J. Ogrodnick Bottom: Fly infected by Entomophthora fungus. Photo: W. Pages People more options. Back to Pathogens Table of Contents Fungi Primary hosts: aphids, whiteflies, leafhoppers, flies, beetles, caterpillars, thrips, and mites; some beetle larvae Key characters: reduced feeding, lethargy; dead insects swell, and may be covered with fungi Crops: many Commercially available: several, including antagonists of fungal disease and a product Metarhizium anisopliae which is used against household cockroaches Some insect species, including many pests, are particularly susceptible to infection by naturally occurring, insect-pathogenic fungi.

Habitat Crops Most crops including soybeans, greenhouse crops, vegetables, cotton, citrus, and ornamentals; also interior plantscapes and forests. Pests Attacked Most insect pests are susceptible to fungal pathogens.

Access on: 12 Nov. Fungal parasites of insects. Annual Review Entomology, v. The Trichomycetes: Fungal Associates of Arthropods.

Access on: 11 Oct. Members of the Harpellales and Asellariales are considered to be gut commensals. An undescribed species of Smittium Trichomycetes pathogenic to mosquito larvae in Australia.

Transactions of the British Mycological Society, v. In addition, several members of the Harpellales parasitize adult black flies Simuliidae , filling their ovaries with fungal cysts, so that the flies disperse the fungus when they try to lay their eggs WHITE et al. Members of Zoopagomycotina have been divided into two families, with the Zoopagaceae restricted to predaceous forms that trap hosts with adhesives and produce a restricted haustorium; and the Cochlonemataceae, which are parasites of rotifers, amoebae, rhizopods, and other fungi BENNY, BENNY, G.

Evolution of entomopathogenicity in fungi. Journal Invertebrate Pathology, v. Some of the species included in these families produce secondary capilliconidia that are effectively dispersed by insects. The Entomophthorales includes the Entomophthora , Pandora , Zoophthora genera, as well as segregate genera. A segregate genus is one that is separate from an existing genus. For example, Entomophaga is a segregate genus of Entomophthora , because some species formerly placed in Entomophthora are now placed in Entomophaga.

Ascomycota are classified into three subphyla. Two of these subphyla do not have pathogenic associations with insects. The role of yeasts as insect endosymbionts. Insect Fungal Associations: Ecology and Evolution. New York: Oxford University Press, The Yeasts: A Taxonomic Study.

Amsterdam: Elsevier, Fungal evolution and taxonomy. BioControl, v. Pezizomycotina are the most numerous and the most morphologically and ecologically complex of the ascomycetes SCHOCH et al. The Ascomycota tree of life: a phylum-wide phylogeny clarifies the origin and evolution of fundamental reproductive and ecological traits.

Systematic Biologists, v. The life cycles often have two states, anamorph asexual state and teleomorph sexual state ; members of the Hypocreales provide good examples of the phenomenon. In some cases, the sexual state may never or only rarely be produced. Under the new classification, anamorphs are often useful for providing taxonomic information. For example, the anamorphs linked to Torrubiella , a genus whose main range of hosts consists of spiders and scale insects, include the Akanthomyces species, which have a wider range of hosts than Gibellula species, which are restricted to spiders HODGE, HODGE, K.

New York: Marcel Dekker, Systematics and evolution of the genus Torrubiella Hypocreales, Ascomycota. Among insect-associated fungi, asexual states often precede the production of sexual states SUNG et al. Phylogenetic classification of Cordyceps and the clavicipitaceous fungi. Studies in Mycology, v. Conidia asexual spores that are formed on insect cadaver can be produced directly on conidiophores as in Metarhizium species on adult insects and larvae.

In some species of Isaria and Akanthomyces , conidia are formed on synnemata, structures formed by fusion of groups of individual conidiophores. A Beauvericin hot spot in the genus Isaria.

Both asexual and sexual spores of insect-associated fungi are typically produced on raised structures, enhancing the opportunity for dispersal to a new host. The production of asexual spores may occur in a stroma, with development of the asci and ascospores.

Perithecia may be immersed in a stroma, as in Cordyceps militaris , C. Fungal Entomopathogens. Insect Pathology, p. Pezizomycotina includes some of the poorly known entomopathogens such as members of the Tubeufiaceae Dothideomycetes.

Species in the Tubeufiaceae have an extensive nutritional range, with many species being saprobic, parasitic on fungi and leaves, or lichen forming with algae KODSUEB et al. Podonectria, a genus in the Pleosporales on scale insects. Mycotaxon, v. Laboulbeniomycetes is an interesting group of insect parasites, though they are not usually considered to be pathogens.

Fungal biotrophic parasites of insects and other arthropods. Insect-Fungal Associations: Ecology and Evolution.

New York: Oxford University Press , Two-celled ascospores germinate on the host surface to produce a haustorium from an attached cell, and the outer cell divides producing a perithecium with determinate growth. No mycelium is produced, and the lack of an asexual state in the order is unique among ascomycetes. A second order, Pyxidiophorales, appears to be mainly mycoparasitic and is also associated with arthropod hosts; these fungi are mycelial and usually have prominent asexual states preceding the development of the sexual state v.

Hypocreales, members of the Sordariomycetes class, are the most commonly known entomopathogens among the ascomycetes. The former Clavicipitaceae has been divided into three monophyletic families: Clavicipitaceae, Cordycipitaceae, and Ophiocordycipitaceae.

Cordycipitaceae contains C. Entomopathogenic asexual states include species of Beauveria , Isaria , Lecanicillium , and other genera. Most Ophiocordycipitaceae members can be distinguished morphologically from the other subphyla due to their often dark stromata and mature ascospores.

In addition to Ophiocordyceps species, the Elaphocordyceps genus parasitizes not only insects but also Elaphomyces , a mycorrhizal ascomycete symbiont of trees SUH et al. Insect symbiosis: derivation of yeast-like endosymbionts within an entomopathogenic lineage. Molecular Biology Evolution, v. However, spider pathogens are mostly found within the Cordycipitaceae, while scale entomopathogens are common in the Clavicipitaceae. Pathogens of ants, termites, or dipterans, and endo symbionts of plant hoppers are often found in the Ophiocordycipitaceae SUNG et al.

Basidiomycetes often are closely associated with insects as their only nutritional resource and as a habitat, and many insects fertilize and disperse these fungi. Insect associations occur in the three subphyla of basidiomycetes Pucciniomycotina, Ustilaginomycotina, and Agaricomycotina , but parasites are found only in the Septobasidiales of the Pucciniomycetes AIME et al.

An overview of the higher level classification of Pucciniomycotina based on combined analyses of nuclear large and small subunit rDNA sequences. Insect pathogenic fungi have to meet several host challenges in order to produce enough new infectious spores in every generation to maintain viable populations. New York: Plenum, Fourth, the fungal pathogen should manage the host cadaver to optimize spore production and dispersal under prevailing environmental conditions Figure 2 ROY et al.

Bizarre interactions and endgames: entomopathogenic fungi and their arthropod hosts. Thus, entomopathogenic fungi display several steps in the development of fungal infections. Figure 2: The diagram illustrates the ways in which pathogenic fungi infect arthropod hosts by asexual or sex spores, proliferate and disperse. A Infection: Entomophthorales fungi infect mainly by large, sticky conidia that penetrate the cuticle directly, and Hypocreales fungi infect by small conidia, which produce appressorial structures.

Ascosphaera spores are also small, enter orally, and infect through the gut epithelium. B Growth: most of Hypocreales and Onygenales proliferate through hyphal growth, and Entomophthorales fungi proliferate through protoplasts.

C Reproduction: asexual conidia of Entomophthorales fungi and sexual ascospores of the Hypocreales are mainly forcibly discharged from the surface of cadavers arrows upwards to the right , whereas very large and thick-walled sexual resting spores of Entomophthorales fungi and asexual conidia of Hypocreales are passively released upward and downward arrows to the left.

Inoculation occurs by direct contact between infectious cadavers and susceptible hosts or indirectly via airborne spores or spores deposited on vegetation or soil particles HESKETH et al. Challenges in modelling complexity of fungal entomopathogens in semi-natural populations of insects.

Laboratory infection experiments show that some minimum number of spores is generally needed to achieve predictable infections INGLIS et al. Laboratory techniques used for entomopathogenic fungi: Hypocreales. Manual of Techniques in Invertebrate Pathology. Amsterdam: Academic, Fungi are heterotrophic organisms, but have to absorb the organic compounds produced by other organisms as their primary sources of energy. The first step to infection is the union of fungal propagules to the host cuticle.

This binding involves non-specific adhesion mechanisms controlled by the hydrophobic properties of the conidial cell wall BOUCIAS et al. Nonspecific factors involved in attachment of entomopathogenic Deuteromycetes to host insect cuticle. Applied Environmental Microbiology, v. The process refers to the interaction between the proteins located in the conidia and the hydrophobic surface of the exoskeleton of the susceptible insects FANG et al.

Cloning of Beauveria bassiana chitinase gene Bbchit1 and its application to improve fungal strain virulence. In some taxa of Hypocreales such as Beauveria , Metarhizium , and Isaria , the hydrophobic properties of conidia are due to the presence of cysteine rich proteins called hydrophobins in the cell wall.

Use of hyphomycetous fungi for managing insect pests. Wallingford: CABI, This process occurs in three successive phases:. Entomopathogens in the Entomophthorales produce conidia that are evolutionarily derived from sporangia.

Fungi: Entomophthorales. Manual of Techniques in Insect Pathology. London: Academic Press, Ultrastructural studies of primary spore formation and discharge in the genus Entomophthora. Some taxa, e. These propagules become easily detached when touched by an insect and adhere to the cuticle through an adhesive droplet that exudes from the capilliconidium tip GLARE et al.

Capilliconidia as infective spores in Zoophthoraphalloides Entomophthorales. Adhesion of the entomopathogenic fungus Beauveria Cordyceps bassiana to substrates.

Applied and Environmental Microbiology, v. Their results show that:. The process of adhesion between the spore and the insect cuticle is mediated by the presence of molecules synthesized by the fungus, called adhesins. A type of adhesin known as MAD1, which is located on the surface of conidia, has been described in Metarhizium anisopliae. A different adhesin-like protein, MAD2, is involved in M. The rhizosphere-competent entomopathogen Metarhizium anisopliae expresses a specific subset of genes in plant root exudate.

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