Insects in Relation to Fungi (complete information)

Fungi have many interesting relationship with insects as commensals, mutuals, and pathogens. Many fungal diseases of plants are transmitted by insects, but apparently no pathogens of vertebrates.

The Laboulbeniales are fungi that live almost exclusively on the integument of Coleoptera, Diptera, and Neuroptera. As commensalistic ectosymbionts, they are transmitted from insect to insect by contact. The insect hosts are rarely killed by the fungi.

Mutualistic ectosymbionts among the fungi are frequently cultivated in “fungus gardens.” Batra and Batra (1967), Francke-Grosmann (1967), Graham (1967), and Weber (1966) provide many details of the relationships.

The insects are gall midges (Lasioptera, Cecidomyiidae), wood wasps (Siricidae and Xiphydriidae), ambrosia beetles (barious Scolytidae, Platypodidae, and Lymexylidae), fungus ants (Atta, Formicidae), and fungus termites. Nutritions food is obtained from fungal saprophytes that grow on cellulose-rich wood or vegetable matter. Some fungus is carried by the adult insects to new locations. Queen Atta ants

A mutualistic relationship exists between Septobasidium fungi and varioi is scale insects in the Southeastern United States. Patches of fungus grow in concentric, annual rings on the bark of trees. Inside are tunnels and chambers enclosing scale insects.

Thus embedded and protected, the scales feed on the plant with their long sucking mouthparts. The fungus apparently derives nourishment parasitically from the living insects and may kill the insect (Couch, 1938). Carry a pellet of fungus in a pouch in the mouth when they fly forth to establish new colonies.

Wood-boring ambrosia beetles and wood wasps have special integumental cavities called mycetangia. Here the fungus is protected from desiccation and is nourished by a secretion. The mycetangia are filled with fungus before the insect leaves its infected gallery. When the beetles bore into a new host or the waps oviposit, the fungus is inoculated in the area where the progeny will develop.

Blue-stain fungi of the genus Ceratocystis are associated with certain scolytid bark beetles. The spores are carried on the body, in mycetangia, or passed with feces. Sapwood moisture of the infected tree is reduced, making the tree more favourable for beetles. The stain lowers the commercial value of the wood.

Dutch elm disease is caused by Ceratocystis ulmi. First discovered in Ohio in 1930, this European disease has killed or has made necessary the destruction of elm trees in many urban areas. It has been recently recognized in California. Scolytus multistriatus and Hylurgopinus rufipes are vectors.

The former feeds on twigs of healthy trees after emergence from infected trees or logs. The beetle then seeks sick trees or freshly cut elm wood to construct its breeding galleries. The healthy trees are infected with spores that cling to the insect. The fungus blocks water- conducting tissues, causing limbs or the whole tree to wilt. The afflicted parts then become suitable breeding sites for more beetles.

Endosymbiotic fungi and yeasts are found in the mycetomes of Hemiptera-Homoptera and intestines of anobiid and cerambycid beetles.

Fungi that are pathogenic to insects normally invade through the integument, but a few enter via the gut. Warm humid environments favour fungal attack.

The fungal filaments and reproductive structures are often evident on the body surface. Species of Entomophthora and Beauveria are common pathogens. In the past, the latter caused serious losses of silkworms in China and Europe. Beauveria globulifera was early noted as causing a contagious disease of the chinch bug Blissus leucopterus (Lygaeidae).

Near the end of the last century, the fungus was mass-produced and distributed to farmers for control of the pest. Entomophthora infects all life stages of insects, especially Diptera, Hemiptera, Lepidoptera, Coleoptera, and Orthoptera. In the fall, Entomophthora muscae causes epidemics among flies, leaving them attached in lifelike postures inside houses or plants.

Insects mechanically transmit fungal pathogens of plants, but this does not preclude intimate biological relationships. The Dutch elm disease mentioned above is an example. Spores of Fusarium moniliforme, causing the disease endo-spesis of figs, are transmitted when the fig wasp pollinates the flowers. A honeydew-like secretion is caused by the ergot fungus Claviceps, when it attacks grasses and cereals. The secretion, infected with spores, is rich in amino acids and attractive to Diptera.

The insect visitors spread disease by carrying the spores externally or by passing them in feces.