Mycangia

The term mycangium (pl., mycangia)(Chinese：贮菌器) is used in biology for special structures on the body of an animal that are adapted for the transport of symbiotic fungi (usually in spore form). This is seen in many xylophagous insects (e.g. horntails and bark beetles), which apparently derive much of their nutrition from the digestion of various fungi that are growing amidst the wood fibers. In some cases, as in ambrosia beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae), the fungi are the sole food, and the excavations in the wood are simply to make a suitable microenvironment for the fungus to grow. In other cases (e.g., the southern pine beetle, Dendroctonus frontalis), wood tissue is the main food, and fungi weaken the defense response from the host plant.

The mites, which have their own type of mycangium (for historical reasons, mite taxonomists use the term sporotheca), ride on or live next to the beetles.

These structures were first systematically described by Helene Francke-Grosmann at 1956. Then Lekh R. Batra coined the word mycangia: modern Latin, from Greek myco 'fungus' + angeion 'vessel'.

The most common function of mycangia is preserving and releasing symbiont (symbiotic inoculum, most are fungi, see next section "Mycangia and symbiotic inoculum"). Usually, the symbiotic inoculum in mycangia will provide great help to their vectors (insect or mites carry symbiont). They could help the vectors adapt to the new environment or become nutrients of the vectors themselves and their descendants.

For example ambrosia beetle (vector) Euwallacea fornicatus carry symbiotic fungus (symbiont) Fusarium. When ambrosia beetle bore the host plant, it releases symbiotic fungus from its mycangium. The symbiotic fungus becomes a plant pathogen weaken the resistance of host plant. In the meantime, the fungus grows quickly in the galleries as the main food of beetle. The offsprings of beetle become mature, they will fill their mycangia with symbiont and hunt for the new host plant.

Therefore, mycangia play an important role in protecting the inoculum from degradation and contamination. The structures of mycangia always look like a pouch or a container with caps or small opening that reduce the possibility of contaminants from outside. How mycangia release their inoculum is still unknown now.

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Wikipedia